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{{Short description|Process of editing the human genome so that the changes are inherited}} | {{Short description|Process of editing the human genome so that the changes are inherited}}{{Improve lead|date=August 2023}} | ||
{{Multiple issues|{{Copy edit|date=July 2023}}{{Improve lead|date=August 2023}}}} | |||
'''Human germline engineering''' is the process by which the ] of an individual is |
'''Human germline engineering''' (HGE) is the process by which the ] of an individual is modified in such a way that the change is heritable. This is achieved by altering the genes of the ], which mature into eggs and sperm. For safety, ethical, and social reasons, the scientific community and the public have concluded that germline editing for reproduction is inappropriate.<ref name=":10">{{Cite journal |last=McGee |first=Andrew |date=2019-10-15 |title=Using the therapy and enhancement distinction in law and policy |url=http://dx.doi.org/10.1111/bioe.12662 |journal=Bioethics |volume=34 |issue=1 |pages=70–80 |doi=10.1111/bioe.12662 |pmid=31617223 |s2cid=204738693 |issn=0269-9702}}</ref><ref name=":11">{{Cite journal |last=Caro-Romero |first=Henry David |date=2020-06-09 |title=Edición genómica heredable: un estudio exploratorio desde la perspectiva del principio bioético de la beneficencia |url=https://revistas.unbosque.edu.co/index.php/RCB/article/view/2732 |journal=Revista Colombiana de Bioética |volume=15 |issue=1 |doi=10.18270/rcb.v15i1.2732 |s2cid=225804689 |issn=2590-9452|doi-access=free }}</ref> HGE is prohibited by law in more than 70 countries<ref name=":3">{{Cite journal |last1=Baylis |first1=Françoise |last2=Darnovsky |first2=Marcy |last3=Hasson |first3=Katie |last4=Krahn |first4=Timothy M. |date=2020-10-01 |title=Human Germline and Heritable Genome Editing: The Global Policy Landscape |journal=The CRISPR Journal |language=en |volume=3 |issue=5 |pages=365–377 |doi=10.1089/crispr.2020.0082 |issn=2573-1599 |pmid=33095042 |s2cid=225053656|doi-access=free }}</ref> and by a binding international treaty of the ]. | ||
In November 2015, a group of Chinese researchers used ]/] to edit single-celled, non-viable embryos to assess its effectiveness. This attempt was unsuccessful; only a small fraction of the embryos successfully incorporated the genetic material and many of the embryos contained a large number of random mutations. The non-viable embryos that were used contained an extra set of chromosomes, which may have been problematic. In 2016, a similar study was performed in China on non-viable embryos with extra sets of chromosomes. This study showed similar results to the first; except that no embryos adopted the desired gene. | |||
In November 2018, researcher ] created the first human genetically edited |
In November 2018, researcher ] created the first human babies from genetically edited embryos, known by their pseudonyms, ]. In May 2019, lawyers in China reported that regulations had been drafted that anyone manipulating the human genome would be held responsible for any related adverse consequences.<ref>{{cite journal |vauthors=Ma H, Marti-Gutierrez N, Park SW, Wu J, Lee Y, Suzuki K, Koski A, Ji D, Hayama T, Ahmed R, Darby H, Van Dyken C, Li Y, Kang E, Park AR, Kim D, Kim ST, Gong J, Gu Y, Xu X, Battaglia D, Krieg SA, Lee DM, Wu DH, Wolf DP, Heitner SB, Belmonte JC, Amato P, Kim JS, Kaul S, Mitalipov S | title = Correction of a pathogenic gene mutation in human embryos | journal = Nature | volume = 548 | issue = 7668 | pages = 413–419 | date = August 2017 | pmid = 28783728 | doi = 10.1038/nature23305 | bibcode = 2017Natur.548..413M | doi-access = free }}{{Expression of Concern|doi=10.1038/nature23305|pmid=28783728|http://retractionwatch.com/2017/09/02/weekend-reads-3/ ''Retraction Watch''|http://retractionwatch.com/2017/10/05/nature-adds-alert-heavily-debated-paper-gene-editing/ ''Retraction Watch''}}</ref> | ||
== Techniques == | == Techniques == | ||
=== CRISPR-Cas9 === | === CRISPR-Cas9 === | ||
{{Main|CRISPR|Cas9}} | {{Main|CRISPR|Cas9}} | ||
The CRISPR-Cas9 system consists of an enzyme called ] and a special piece of ] (gRNA). Cas9 acts as a pair of ‘molecular scissors’ that can cut the DNA at a specific location in the genome so that genes can be added or removed. The guide RNA has complementary bases to those at the target location, so it binds only there. Once bound Cas9 makes a cut across both DNA strands allowing base pairs to inserted/removed. Afterwards, the cell recognizes that the DNA is damaged and tries to repair it.<ref>{{cite journal | vauthors = Ormond KE, Mortlock DP, Scholes DT, Bombard Y, Brody LC, Faucett WA, Garrison NA, Hercher L, Isasi R, Middleton A, Musunuru K, Shriner D, Virani A, Young CE | display-authors = 6 | title = Human Germline Genome Editing | journal = American Journal of Human Genetics | volume = 101 | issue = 2 | pages = 167–176 | date = August 2017 | pmid = 28777929 | pmc = 5544380 | doi = 10.1016/j.ajhg.2017.06.012 }}</ref> | |||
Although |
Although CRISPR/Cas9 can be used in humans,<ref>{{Cite journal|last1=Rodríguez-Rodríguez|first1=Diana Raquel|last2=Ramírez-Solís|first2=Ramiro|last3=Garza-Elizondo|first3=Mario Alberto|last4=Garza-Rodríguez|first4=María De Lourdes|last5=Barrera-Saldaña|first5=Hugo Alberto|date=April 2019|title=Genome editing: A perspective on the application of CRISPR/Cas9 to study human diseases (Review)|journal=International Journal of Molecular Medicine|volume=43|issue=4|pages=1559–1574|doi=10.3892/ijmm.2019.4112|issn=1791-244X|pmc=6414166|pmid=30816503}}</ref> it is more commonly used in other species or cell culture systems, including in experiments to study genes potentially involved in human diseases. | ||
== Speculative uses == | |||
{{Main|Preimplantation genetic diagnosis}}{{Cleanup rewrite|date=July 2023|There are two copies of the section that go into different levels of detail and subject knowledge is necessary to merge them|section=yes}} | |||
Another way to modify the human genome involves analyzing human embryos to identify genes associated with disease, and selecting embryos that have the desired genetic makeup. This is called PGD, or Preimplantation Genetic Diagnosis. IVF, or ], is often used to obtain embryos for evaluation of the genome – alternatively, ] can be screened prior to fertilization. The technique was first used in 1989. | |||
Genetic engineering is in widespread use, particularly in agriculture. Human germline engineering has two potential applications: prevent genetic disorders from passing to descendants, and to modify traits such as height that are not disease related. For example, the ] has a genetic mutation in the ] gene that suppresses the expression of CCR5. This confers ]. Modifying human embryos to give the CCR5 Δ32 allele protects them from the disease. | |||
PGD is used primarily to select embryos for ] when there are possible genetic defects, allowing mutated or disease-related alleles to be identified and excluded from selection. It is especially useful when one or both parents carry a heritable genetic disease. PGD can also be used to select for embryos of a certain sex, which is useful to avoid sex-linked genetic disorders like hemophilia, which is more common in males. Infants born with traits selected by PGD are sometimes considered to be designer babies.<ref>{{Cite web |last1=Jin |first1=Shouguang |last2=March 27 |first2=University of Florida {{!}} |last3=ET |first3=2015 01:17pm |date=27 March 2015 |title=Are Tools for Tweaking Embryonic Cells Ethical? (Op-Ed) |url=https://www.livescience.com/50284-are-tools-for-tweaking-embryonic-cells-ethical.html |access-date=2018-12-05 |website=Live Science}}</ref> | |||
⚫ | An other use would be to cure genetic disorders. In the first study published regarding human germline engineering, the researchers attempted to edit the '']'' gene which codes for the human ] protein. ''HBB'' mutations produce ], which can be fatal.<ref name=":1">{{cite journal |last1=Cyranoski |first1=David |last2=Reardon |first2=Sara |date=22 April 2015 |title=Chinese scientists genetically modify human embryos |journal=Nature |pages=nature.2015.17378 |doi=10.1038/nature.2015.17378 |s2cid=87604469}}</ref> Genome editing in patients who have these ''HBB'' mutations would leave copies of the unmutated gene, effectively curing the disease. If the germline could be edited, this normal copy of the ''HBB'' genes could be passed on to future generations. | ||
One application of PGD is the selection of ‘]’, children who are born to provide a transplant (of an organ or group of cells) to a sibling with a usually life-threatening disease. Savior siblings are conceived through IVF and then screened using PGD to analyze genetic similarity to the child needing a transplant, in order to reduce the risk of rejection. | |||
==== Detailed description ==== | |||
Embryos for PGD are obtained from IVF procedures in which the oocyte is artificially fertilized by sperm. Oocytes from the woman are harvested following controlled ovarian hyper stimulation (COH), which involves fertility treatments to induce production of multiple oocytes. After harvesting the oocytes, they are fertilized in vitro, either during incubation with multiple sperm cells in culture, or via ] (ICSI), where sperm is directly injected into the oocyte.<ref name=":6" /> Such tests include amniocentesis, ultrasounds, and other preimplantation genetic diagnostic tests. These tests are quite common, and reliable, as we talk about them today; however, in the past when they were first introduced, they too were scrutinized.<ref name=":6" /> The resulting embryos are usually cultured for 3–6 days, allowing them to reach the blastomere or blastocyst stage. Once embryos reach the desired stage of development, cells are biopsied and genetically screened. The screening procedure varies based on the nature of the disorder being investigated. | |||
] (PCR) is a process in which DNA sequences are amplified to produce many more copies of the same segment, allowing screening of large samples and identification of specific genes. The process is often used when screening for monogenic disorders, such as cystic fibrosis. | |||
Another screening technique, ] (FISH) uses fluorescent probes which specifically bind to highly complementary sequences on chromosomes, which can then be identified using fluorescence microscopy. FISH is often used when screening for chromosomal abnormalities such as aneuploidy, making it a useful tool when screening for disorders such as Down syndrome.<ref name=":6" /> | |||
Following screening, embryos with the desired trait (or lacking an undesired trait such as a mutation) are transferred into the mother's uterus, then allowed to develop naturally. | |||
== Conceivable uses == | |||
Human germline engineering could be used to heritably cure genetic disorders and other diseases, and to give specific traits to human babies. For example, ] has a genetic mutation in the ] gene (which codes for a protein on the surface of white blood cells, targeted by the HIV virus) that deactivates the expression of CCR5, conferring ]. HIV/AIDS carries a large disease burden and is incurable (see ]). One proposal is to genetically modify human embryos to give the CCR5 Δ32 allele to people. | |||
⚫ | |||
=== Designer babies === | === Designer babies === | ||
{{Main articles|Designer baby}} | {{Main articles|Designer baby}} | ||
] modifications to humans yield "]", with deliberately-selected traits, possibly extending to its entire genome.<ref name=":2">National Academies of Sciences, Engineering, and Medicine. 2017. Human Genome Editing: Science, Ethics, and Governance. Washington, DC: The National Academies Press. doi: 10.17226/24623.</ref> HGE potentially allows for enhancement of these traits.<ref name=":2" /> The concept has produced strong objections, particularly among bioethicists.<ref>{{Cite book|url={{google books|plainurl=y|id=iWqBAgAAQBAJ}}|title=New Horizons in Medical Anthropology: Essays in Honour of Charles Leslie|last1=Lock|first1=Margaret|last2=Nichter|first2=Mark | name-list-style = vanc |date=2003-09-02|publisher=Routledge|isbn=9781134471287}}</ref> | |||
⚫ | In a 2019 animal study with Liang Guang |
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== State of research == | |||
⚫ | |||
⚫ | |||
⚫ | === Lack of |
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⚫ | The lack of |
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⚫ | |||
⚫ | === He Jiankui |
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{{Main|He Jiankui affair}}{{Summary too long|date=July 2023}} | |||
On 25 November 2018, two days before the Second International Summit on Human Genome Editing in Hong Kong, ], a Chinese researcher of the Southern University of Science and Technology, released a video on YouTube announcing that he and his colleagues have “created” the world's first genetically altered babies, Lulu and Nana. | |||
⚫ | In a 2019 animal study with Liang Guang small spotted pigs, precise editing of the ] signal peptide yielded increased muscle mass. Myostatin is a negative regulator of muscle growth, so by mutating the gene's signal peptide regions could be promoted. One study mutated myostatin genes in 955 embryos at several locations with CRISPR/cas9 and implanted them into five surrogates, resulting in 16 piglets. Only specific mutations to the myostatin signal peptide increased muscle mass, mainly due to an increase in muscle fibers.<ref>{{Cite journal |last1=Li |first1=Ruiqiang |last2=Zeng |first2=Wu |last3=Ma |first3=Miao |last4=Wei |first4=Zixuan |last5=Liu |first5=Hongbo |last6=Liu |first6=Xiaofeng |last7=Wang |first7=Min |last8=Shi |first8=Xuan |last9=Zeng |first9=Jianhua |last10=Yang |first10=Linfang |last11=Mo |first11=Delin |last12=Liu |first12=Xiaohong |last13=Chen |first13=Yaosheng |last14=He |first14=Zuyong |date=February 2020 |title=Precise editing of myostatin signal peptide by CRISPR/Cas9 increases the muscle mass of Liang Guang Small Spotted pigs |url=http://link.springer.com/10.1007/s11248-020-00188-w |journal=Transgenic Research |language=en |volume=29 |issue=1 |pages=149–163 |doi=10.1007/s11248-020-00188-w |pmid=31927726 |s2cid=255111445 |issn=0962-8819}}</ref> A similar mice study knoced out the myostatin gene, which also increased their muscle mass.<ref>{{Cite journal |last=Professor |first=Apostolos Stergioulas, Ph D. |title=Gene doping in modern sport |date=2021-02-04 |url=https://www.biologyofexercise.com/abs_5_1.html |access-date=2022-12-06 |journal=Journal Biology of Exercise |volume=5 |language=en-US |doi=10.4127/jbe.2009.0021}}</ref> This showed that muscle mass could be increased with germline editing, which is likely applicable to humans because the myostatin gene regulates human muscle growth.<ref>{{Cite journal |last1=Gonzalez-Cadavid |first1=Nestor F. |last2=Taylor |first2=Wayne E. |last3=Yarasheski |first3=Kevin |last4=Sinha-Hikim |first4=Indrani |last5=Ma |first5=Kun |last6=Ezzat |first6=Shereen |last7=Shen |first7=Ruoqing |last8=Lalani |first8=Rukhsana |last9=Asa |first9=Sylvia |last10=Mamita |first10=Mohamad |last11=Nair |first11=Gouri |last12=Arver |first12=Stefan |last13=Bhasin |first13=Shalender |date=1998-12-08 |title=Organization of the human myostatin gene and expression in healthy men and HIV-infected men with muscle wasting |journal=Proceedings of the National Academy of Sciences |language=en |volume=95 |issue=25 |pages=14938–14943 |doi=10.1073/pnas.95.25.14938 |issn=0027-8424 |pmc=24554 |pmid=9843994|doi-access=free |bibcode=1998PNAS...9514938G }}</ref> | ||
He explained the details of his experiment in his address at the Hong Kong conference. He and his team had recruited eight couples through an HIV volunteer group named Baihualin (BHL) China League (one couple later withdrew from the research). All the male participants are HIV-positive, and all female participants are HIV-negative. The participants' sperm was “washed off” to get rid of HIV and then injected into eggs collected from the female participants. By using clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9, a gene editing technique, they disabled a gene called ] in the embryos, aiming to close the protein doorway that allows HIV to enter a cell and make the subjects immune to the HIV virus. The process led to at least one successful pregnancy and the birth of the twin baby girls, ].<ref name="Statuproar">{{cite news |last1=Begley |first1=Sharon |date=28 November 2018 |title=Amid uproar, Chinese scientist defends creating gene-edited babies |work=STAT News |url=https://www.statnews.com/2018/11/28/chinese-scientist-defends-creating-gene-edited-babies/}}</ref><ref name="sina1127">{{cite web |date=27 November 2018 |title=复盘贺建奎的人生轨迹:是谁给了他勇气 |url=http://news.sina.com.cn/c/2018-11-27/doc-ihpevhck8869227.shtml |access-date=28 November 2018 |publisher=] |language=zh}}</ref> Researcher ] has discovered an impact the ] has on the memory function the brain.<ref>{{Cite web |date=2019-01-21 |title=He Jiankui Fired in Wake of CRISPR Babies Investigation |url=https://www.genengnews.com/news/he-jiankui-fired-in-wake-of-crispr-babies-investigation/ |access-date=2019-04-18 |website=GEN - Genetic Engineering and Biotechnology News}}</ref> | |||
== Research == | |||
A major concern has been that He Jiankui's attempts to cripple CCR5, the gene for a protein on immune cells that HIV uses to infect the cells, also made “off-target” changes elsewhere in the girls' genomes. Those changes could cause cancer or other problems. He contends that the babies have no such off-target mutations, although some scientists are skeptical of the evidence offered so far.<ref>{{Cite web |date=2018-11-28 |title=Amid uproar, Chinese scientist defends creating gene-edited babies |url=https://www.statnews.com/2018/11/28/chinese-scientist-defends-creating-gene-edited-babies/ |access-date=2019-04-18 |website=STAT}}</ref> | |||
⚫ | HGE is widely debated, and more than 40 countries formally outlaw it.<ref name="NAT-20150312">{{cite journal |vauthors=Lanphier E, Urnov F, Haecker SE, Werner M, Smolenski J |date=March 2015 |title=Don't edit the human germ line |journal=Nature |volume=519 |issue=7544 |pages=410–1 |bibcode=2015Natur.519..410L |doi=10.1038/519410a |pmid=25810189 |doi-access=free}}</ref> No legislation explicitly prohibits germline engineering in the United States. The '']'' bans the use of ] funds to engage in human germline modification research.<ref>{{cite journal | vauthors = Cohen IG, Adashi EY | title = SCIENCE AND REGULATION. The FDA is prohibited from going germline | journal = Science | volume = 353 | issue = 6299 | pages = 545–6 | date = August 2016 | pmid = 27493171 | doi = 10.1126/science.aag2960 | bibcode = 2016Sci...353..545C | s2cid = 206651381 }}</ref> In April 2015, a research team published an unsuccessful experiment in which they used CRISPR to edit a gene that is associated with blood disease in non-living human embryos. | ||
People inherit two copies of CCR5, one from each parent. He chose the gene as a target because he knew that about 1% of Northern European populations are born with both copies missing 32 base pairs, resulting in a truncated protein that does not reach the cell surface. These people, known as CCR5Δ32 ], appear healthy and are highly resistant to HIV infection. | |||
⚫ | researchers using CRISPR/Cas9 have run into issues when it comes to mammals due to their complex ]. Studies in microorganisms have examined loss of function genetic screening. Some studies used mice as a subject. Because RNA processes differ between bacteria and mammalian cells, researchers have had difficulties coding for mRNA's translated data without RNA interference. Studies have successfully used a Cas9 nuclease with a single guide RNA to allow for larger knockout regions in mice.<ref>{{cite journal | last1 = Wang | first1 = Tim | display-authors = etal | year = 2014 | title = Genetic screens in human cells using the CRISPR-Cas9 system | journal = Science | volume = 343 | issue = 6166| pages = 80–4 | doi = 10.1126/science.1246981 | bibcode = 2014Sci...343...80W | pmc = 3972032 | pmid = 24336569 }}</ref> | ||
In the embryos, He's team designed CRISPR to cut CCR5 at the base pair at one end of the natural deletion. The error-prone cell-repair mechanism, which CRISPR depends on to finish knocking out genes, then deleted 15 base pairs in one of Lulu's copies of the gene, but none in the other. With one normal CCR5, she is expected to have no protection from HIV. Nana, according to the data He presented in a slide at an international genome-editing summit held in November 2018 in Hong Kong, China, had bases added to one CCR5 copy and deleted from the other, which likely would cripple both genes and provide HIV resistance. | |||
⚫ | === Lack of international regulation === | ||
He added the genes for the CRISPR machinery almost immediately after each embryo was created through in vitro fertilization, but several researchers who closely studied the slide caution that it may have done its editing after Nana's embryo was already past the one-cell stage. That means she could be a genetic “mosaic” who has some unaffected cells with normal CCR5—and ultimately might have no protection from HIV. | |||
⚫ | The lack of international regulation led researchers to attempt to create an international framework of ethical guidelines. The framework lacks the requisite international treaties for enforcement. At the first International Summit on Human Gene Editing in December 2015 researchers issued the first international guidelines.<ref>{{Cite web|url=http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=12032015a|title=On Human Gene Editing: International Summit Statement|website=www8.nationalacademies.org|access-date=2019-04-18}}</ref> These guidelines allowed pre-clinical research into gene editing in human cells as long as the embryos were not used to implant pregnancy. Genetic alteration of somatic cells for therapeutic proposes was considered ethically acceptable in part because somatic cells cannot pass modifications to subsequent generations. However the lack of consensus and the risks of inaccurate editing led the conference to call for restraint on germline modifications. | ||
⚫ | On March 13, 2019 researchers ], ], ], ], Paul Bergfrom and others called for a framework that did not foreclose any outcome, but included a voluntary pledge and a call for a coordinating body to monitor the HGE moratorium with an attempt to reach social consensus before furthering research.<ref>{{cite journal | title = Germline gene-editing research needs rules | journal = Nature | volume = 567 | issue = 7747 | pages = 145 | date = March 2019 | pmid = 30867612 | doi = 10.1038/d41586-019-00788-5 | bibcode = 2019Natur.567..145. | doi-access = free }}</ref> ] announced on December 18, 2018 plans to convene an intentional committee on the topic.<ref>{{Cite web|url=https://www.who.int/ethics/topics/human-genome-editing/en/|archive-url=https://web.archive.org/web/20190222155933/https://www.who.int/ethics/topics/human-genome-editing/en/|url-status=dead|archive-date=February 22, 2019|title=WHO {{!}} Gene editing|website=WHO|access-date=2019-04-18}}</ref> | ||
Aside from the primary HIV concerns, the gene edits may have inadvertently altered cognitive function. Researchers showed in 2016 that knocking out one or both CCR5s in mice enhances their memory and cognition. A subsequent study that crippled CCR5 in mice found that, compared with control animals, the mutants recovered from strokes more quickly and had improved motor and cognitive functions following traumatic brain injury. The later study, in the 21 February issue of Cell, also included an analysis of 68 stroke patients who had one copy of CCR5 with the HIV resistance mutation; it concluded they had improved recovery, too. | |||
⚫ | === He Jiankui === | ||
On the night of November 26, 122 Chinese scientists issued a statement strongly condemning He's action as unethical. They stated that while CRISPR-Cas is not a new technology, it involves serious off-target risks and associated ethical considerations, and so should not be used to produce gene-altered babies. They described He's experiment as “crazy” and “a huge blow to the global reputation and development of Chinese science”. The Scientific Ethics Committee of the Academic Divisions of the ] posted a statement declaring their opposition to any clinical use of genome editing on human embryos, noting that “the theory is not reliable, the technology is deficient, the risks are uncontrollable, and ethics and regulations prohibit the action”.<ref name="PC-20150418">{{cite journal |vauthors=Liang P, Xu Y, Zhang X, Ding C, Huang R, Zhang Z, Lv J, Xie X, Chen Y, Li Y, Sun Y, Bai Y, Songyang Z, Ma W, Zhou C, Huang J |date=May 2015 |title=CRISPR/Cas9-mediated gene editing in human tripronuclear zygotes |journal=Protein & Cell |volume=6 |issue=5 |pages=363–372 |doi=10.1007/s13238-015-0153-5 |pmc=4417674 |pmid=25894090}}</ref> The Chinese Academy of Engineering released a statement on November 28, calling on scientists to improve self-discipline and self-regulation, and to abide by corresponding ethical principles, laws, and regulations. Finally, the Chinese Academy of Medical Sciences published a correspondence in The Lancet, stating that they are “opposed to any clinical operation of human embryo genome editing for reproductive purposes." | |||
{{Excerpt|He Jiankui affair}} | |||
=== Major studies |
=== Major studies === | ||
* The first known |
* The first known HGE research was by Chinese researchers in April 2015 in ''Protein and Cell''.<ref name="PC-20150418">{{cite journal |vauthors=Liang P, Xu Y, Zhang X, Ding C, Huang R, Zhang Z, Lv J, Xie X, Chen Y, Li Y, Sun Y, Bai Y, Songyang Z, Ma W, Zhou C, Huang J |date=May 2015 |title=CRISPR/Cas9-mediated gene editing in human tripronuclear zygotes |journal=Protein & Cell |volume=6 |issue=5 |pages=363–372 |doi=10.1007/s13238-015-0153-5 |pmc=4417674 |pmid=25894090}}</ref> The researchers used tripronuclear (3PN) ] fertilized by two sperm and therefore non-viable, to investigate ]-mediated gene editing in human cells. The researchers found that while CRISPR/Cas9 could effectively cleave the ], the efficiency of ] directed repair of ''CRISPR/Cas9'' was inefficient and failed in a majority of trials. Problems arose such as off-target cleavage and the competitive recombination of the endogenous delta-globin with ''CRISPR/Cas9'' led to unexpected mutation. The study results indicated that ''HBB'' repair in the embryos occurred preferentially through alternative pathways. In the end only 4 of the 54 zygotes carried the intended genetic information, and even then the successfully edited embryos were mosaics containing the preferential genetic code and the mutation. | ||
* In March 2017, |
* In March 2017, researchers claimed to have successfully edited three viable human embryos.<ref>{{cite journal |vauthors=Tang L, Zeng Y, Du H, Gong M, Peng J, Zhang B, Lei M, Zhao F, Wang W, Li X, Liu J |date=June 2017 |title=CRISPR/Cas9-mediated gene editing in human zygotes using Cas9 protein |journal=Molecular Genetics and Genomics |volume=292 |issue=3 |pages=525–533 |doi=10.1007/s00438-017-1299-z |pmid=28251317 |s2cid=16358211}}</ref> The study showed that CRISPR/Cas9 is could effectively be used as a gene-editing tool in human 2PN zygotes, which could potentially lead to a viable pregnancy. The researchers used injection of Cas9 protein complexed with the relevant sgRNAs and homology donors into human embryos. The researchers found homologous recombination-mediated alteration in ''CRISPR/Cas9'' and '']''. The researchers also noted the limitations of their study and called for further research. | ||
* |
* An August 2017 study reported the successful use of ] to edit out a mutation responsible for ].<ref>{{cite journal |display-authors=6 |vauthors=Ma H, Marti-Gutierrez N, Park SW, Wu J, Lee Y, Suzuki K, Koski A, Ji D, Hayama T, Ahmed R, Darby H, Van Dyken C, Li Y, Kang E, Park AR, Kim D, Kim ST, Gong J, Gu Y, Xu X, Battaglia D, Krieg SA, Lee DM, Wu DH, Wolf DP, Heitner SB, Belmonte JC, Amato P, Kim JS, Kaul S, Mitalipov S |date=August 2017 |title=Correction of a pathogenic gene mutation in human embryos |journal=Nature |volume=548 |issue=7668 |pages=413–419 |bibcode=2017Natur.548..413M |doi=10.1038/nature23305 |pmid=28783728 |doi-access=free}}{{Expression of Concern|doi=10.1038/nature23305|pmid=28783728|http://retractionwatch.com/2017/09/02/weekend-reads-3/ ''Retraction Watch''|http://retractionwatch.com/2017/10/05/nature-adds-alert-heavily-debated-paper-gene-editing/ ''Retraction Watch''}}</ref> The study looked at heterozygous '']'' mutation in human embryos. The study claimed precise CRISPR/Cas9 and homology-directed repair response with high accuracy and precision. By modifying the cell cycle stage at which the DSB was induced, they were able to avoid ] in cleaving embryos, prominent in earlier studies, and achieve a large percentage of homozygous embryos carrying the wild-type '']'' gene without evidence of unintended mutations. The researchers concluded that the technique may be used to correct mutations in human embryos. The claims of this study were however pushed back on by critics who argued the evidence was unpersuasive. | ||
* |
* A June 2018 study researchers reported a potential link for edited cells having increased cancerous potential.<ref>{{cite journal |vauthors=Haapaniemi E, Botla S, Persson J, Schmierer B, Taipale J |date=July 2018 |title=CRISPR-Cas9 genome editing induces a p53-mediated DNA damage response |journal=Nature Medicine |volume=24 |issue=7 |pages=927–930 |doi=10.1038/s41591-018-0049-z |pmid=29892067 |s2cid=47018050 |hdl-access=free |hdl=10138/303675}}</ref> The study reported that CRISPR/Cas9 induced DNA damage response and stopped the cell cycle. The study was conducted in human ] cells, and the use of ] led to a selection against cells with a functional ] pathway. The study concluded that ] inhibition might increase HGE efficiency and that ] function would need to be watched when developing CRISPR/Cas9 based therapy. | ||
* |
* A November 2018 study of using CRISPR/Cas9 to correct a single mistaken amino acid in 16 out of 18 attempts in a human embryo. The unusual level of precision was achieved with a base editor (BE) system that was constructed by fusing the ] to the dCas9 protein. The BE system efficiently edited the targeted C to T or G to A without the use of a donor and without DBS formation. The study focused on the '']'' mutation that is causative for ]. The study supported the corrective value of gene therapy for the ''FBN1'' mutation in both somatic and germline cells.<ref>{{cite journal |vauthors=Zeng Y, Li J, Li G, Huang S, Yu W, Zhang Y, Chen D, Chen J, Liu J, Huang X |date=November 2018 |title=Correction of the Marfan Syndrome Pathogenic FBN1 Mutation by Base Editing in Human Cells and Heterozygous Embryos |url= |journal=Molecular Therapy |language=en |volume=26 |issue=11 |pages=2631–2637 |doi=10.1016/j.ymthe.2018.08.007 |pmc=6224777 |pmid=30166242}}</ref> | ||
== Ethical and moral debates == | == Ethical and moral debates == | ||
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{{See also|Designer baby#Ethical_considerations}} | {{See also|Designer baby#Ethical_considerations}} | ||
As early in the history of biotechnology as 1990, there have been |
As early in the history of biotechnology as 1990, there have been researchers opposed to attempts to modify the human ] using these new tools,<ref>. cioms.ch</ref> and such concerns have continued as technology progressed.<ref>{{cite journal | vauthors = Smith KR, Chan S, Harris J | title = Human germline genetic modification: scientific and bioethical perspectives | journal = Archives of Medical Research | volume = 43 | issue = 7 | pages = 491–513 | date = October 2012 | pmid = 23072719 | doi = 10.1016/j.arcmed.2012.09.003 }}</ref><ref>{{cite journal |last1=Reardon |first1=Sara |title=US science advisers outline path to genetically modified babies |journal=Nature |date=14 February 2017 |pages=nature.2017.21474 |doi=10.1038/nature.2017.21474 |doi-access=free }}</ref> In March 2015, with the advent of new techniques like ], researchers urged a worldwide moratorium on clinical use of gene editing technologies to edit the human genome in a way that can be inherited.<ref name="NYT-20150319">{{cite news | last = Wade | first = Nicholas | name-list-style = vanc | title = Scientists Seek Ban on Method of Editing the Human Genome | url = https://www.nytimes.com/2015/03/20/science/biologists-call-for-halt-to-gene-editing-technique-in-humans.html | date =19 March 2015 | work = ] | access-date = 20 March 2015 | quote = The biologists writing in Science support continuing laboratory research with the technique, and few if any scientists believe it is ready for clinical use.}}</ref> In April 2015, researchers reported results of basic research to edit the DNA of non-viable human embryos using CRISPR, creating controversy.<ref name="NYT-20150423">{{cite news |last=Kolata |first=Gina | name-list-style = vanc |title=Chinese Scientists Edit Genes of Human Embryos, Raising Concerns |url=https://www.nytimes.com/2015/04/24/health/chinese-scientists-edit-genes-of-human-embryos-raising-concerns.html |date=23 April 2015 |work=] |access-date=24 April 2015 }}</ref> | ||
A committee of the American ] and ] gave support to human genome editing in 2017<ref>{{Cite news|url=https://www.nytimes.com/2017/02/14/health/human-gene-editing-panel.html|title=Human Gene Editing Receives Science Panel's Support|last=Harmon|first=Amy| name-list-style = vanc |date=2017-02-14|newspaper=The New York Times|access-date=2017-02-17|issn=0362-4331}}</ref><ref>{{cite web|last1=Committee on Human Gene Editing: Scientific, Medical, and Ethical Considerations|title=Human Genome Editing: Science, Ethics, and Governance|url=http://nationalacademies.org/gene-editing/consensus-study/index.htm|website=nationalacademies.org|publisher=National Academy of Sciences; National Academy of Medicine|access-date=21 February 2017}}</ref> once answers have been found to safety and efficiency problems "but only for serious conditions under stringent oversight."<ref>{{Cite web|url=https://nypost.com/2017/02/14/scientists-ok-genetically-engineering-babies/|title=Scientists OK genetically engineering babies|date=2017-02-14|website=New York Post|publisher=Reuters|access-date=2017-02-17}}</ref> The ]'s Council on Ethical and Judicial Affairs stated that "genetic interventions to enhance traits should be considered permissible only in severely restricted situations: (1) clear and meaningful benefits to the fetus or child; (2) no trade-off with other characteristics or traits; and (3) equal access to the genetic technology, irrespective of income or other socioeconomic characteristics."<ref>{{cite journal | title = Ethical issues related to prenatal genetic testing. The Council on Ethical and Judicial Affairs, American Medical Association | journal = Archives of Family Medicine | volume = 3 | issue = 7 | pages = 633–642 | date = July 1994 | pmid = 7921302 | doi = 10.1001/archfami.3.7.633 }}</ref> | A committee of the American ] and ] gave support to human genome editing in 2017<ref>{{Cite news|url=https://www.nytimes.com/2017/02/14/health/human-gene-editing-panel.html|title=Human Gene Editing Receives Science Panel's Support|last=Harmon|first=Amy| name-list-style = vanc |date=2017-02-14|newspaper=The New York Times|access-date=2017-02-17|issn=0362-4331}}</ref><ref>{{cite web|last1=Committee on Human Gene Editing: Scientific, Medical, and Ethical Considerations|title=Human Genome Editing: Science, Ethics, and Governance|url=http://nationalacademies.org/gene-editing/consensus-study/index.htm|website=nationalacademies.org|publisher=National Academy of Sciences; National Academy of Medicine|access-date=21 February 2017}}</ref> once answers have been found to safety and efficiency problems "but only for serious conditions under stringent oversight."<ref>{{Cite web|url=https://nypost.com/2017/02/14/scientists-ok-genetically-engineering-babies/|title=Scientists OK genetically engineering babies|date=2017-02-14|website=New York Post|publisher=Reuters|access-date=2017-02-17}}</ref> The ]'s Council on Ethical and Judicial Affairs stated that "genetic interventions to enhance traits should be considered permissible only in severely restricted situations: (1) clear and meaningful benefits to the fetus or child; (2) no trade-off with other characteristics or traits; and (3) equal access to the genetic technology, irrespective of income or other socioeconomic characteristics."<ref>{{cite journal | title = Ethical issues related to prenatal genetic testing. The Council on Ethical and Judicial Affairs, American Medical Association | journal = Archives of Family Medicine | volume = 3 | issue = 7 | pages = 633–642 | date = July 1994 | pmid = 7921302 | doi = 10.1001/archfami.3.7.633 }}</ref> | ||
Several religious positions have been published with regards to human germline engineering. According to them, many see germline modification as being more moral than the alternative, which would be either discarding of the embryo, or birth of a diseased human. The main conditions when it comes to whether or not it is morally and ethically acceptable lie within the intent of the modification, and the conditions in which the engineering is done.<ref name=":5">{{Cite book |last=Cole-Turner |first=Ronald |url= |
Several religious positions have been published with regards to human germline engineering. According to them, many see germline modification as being more moral than the alternative, which would be either discarding of the embryo, or birth of a diseased human. The main conditions when it comes to whether or not it is morally and ethically acceptable lie within the intent of the modification, and the conditions in which the engineering is done.<ref name=":5">{{Cite book |last=Cole-Turner |first=Ronald |url={{google books|plainurl=y|id=E3qsPJb44Q8C|page=7}}|page=7 |title=Design and Destiny: Jewish and Christian Perspectives on Human Germline Modification |date=2008 |publisher=MIT Press |isbn=9780262533010}}</ref> | ||
Ethical claims about germline engineering include beliefs that every ] has a right to remain genetically unmodified, that parents hold the right to genetically modify their offspring, and that every child has the right to be born free of preventable diseases.<ref name="Evolution">{{cite journal | vauthors = Powell R, Buchanan A | title = Breaking evolution's chains: the prospect of deliberate genetic modification in humans | journal = The Journal of Medicine and Philosophy | volume = 36 | issue = 1 | pages = 6–27 | date = February 2011 | pmid = 21228084 | doi = 10.1093/jmp/jhq057 }}</ref><ref name="Baylis, Francoise 2004">{{cite journal | vauthors = Baylis F, Robert JS | title = The inevitability of genetic enhancement technologies | journal = Bioethics | volume = 18 | issue = 1 | pages = 1–26 | year = 2004 | pmid = 15168695 | doi = 10.1111/j.1467-8519.2004.00376.x }}</ref><ref>{{cite book|last=Evans|first=John| name-list-style = vanc |title=Playing God?: Human Genetic Engineering and the Rationalization of Public Bioethical Debate|year=2002|publisher=University of Chicago Press | isbn = 978-0-226-22262-2 }}</ref> For parents, genetic engineering could be seen as another child enhancement technique to add to diet, exercise, education, training, cosmetics, and plastic surgery.<ref name="Enhancement"> |
Ethical claims about germline engineering include beliefs that every ] has a right to remain genetically unmodified, that parents hold the right to genetically modify their offspring, and that every child has the right to be born free of preventable diseases.<ref name="Evolution">{{cite journal | vauthors = Powell R, Buchanan A | title = Breaking evolution's chains: the prospect of deliberate genetic modification in humans | journal = The Journal of Medicine and Philosophy | volume = 36 | issue = 1 | pages = 6–27 | date = February 2011 | pmid = 21228084 | doi = 10.1093/jmp/jhq057 }}</ref><ref name="Baylis, Francoise 2004">{{cite journal | vauthors = Baylis F, Robert JS | title = The inevitability of genetic enhancement technologies | journal = Bioethics | volume = 18 | issue = 1 | pages = 1–26 | year = 2004 | pmid = 15168695 | doi = 10.1111/j.1467-8519.2004.00376.x }}</ref><ref>{{cite book|last=Evans|first=John| name-list-style = vanc |title=Playing God?: Human Genetic Engineering and the Rationalization of Public Bioethical Debate|year=2002|publisher=University of Chicago Press | isbn = 978-0-226-22262-2 }}</ref> For parents, genetic engineering could be seen as another child enhancement technique to add to diet, exercise, education, training, cosmetics, and plastic surgery.<ref name="Enhancement">{{Cite web |title=Center for Health Ethics - MU School of Medicine |url=https://medicine.missouri.edu/centers-institutes-labs/health-ethics |access-date=2024-11-23 |website=medicine.missouri.edu|archive-url=https://web.archive.org/web/20131203040308/http://ethics.missouri.edu/Gene-Therapy.aspx |archive-date=3 December 2013 |date=25 April 2013}}</ref><ref name="Roco_Bainbridge_2002">{{cite journal | vauthors = Roco MC, Bainbridge WS | journal = Journal of Nanoparticle Research | year = 2002 | volume = 4 | issue = 4 | pages = 281–295 | doi = 10.1023/A:1021152023349|title=Converging Technologies for Improving Human Performance: Integrating From the Nanoscale | bibcode = 2002JNR.....4..281R | s2cid = 136290217 }}</ref> Another theorist claims that moral concerns limit but do not prohibit germline engineering.<ref>{{cite journal |last1=Allhoff |first1=Fritz |title=Germ-Line Genetic Enhancement and Rawlsian Primary Goods |journal=Kennedy Institute of Ethics Journal |date=2005 |volume=15 |issue=1 |pages=39–56 |doi=10.1353/ken.2005.0007 |pmid=15881795 |citeseerx=10.1.1.566.171 |s2cid=14432440 }}</ref> | ||
=== Consent === | === Consent === | ||
One issue related to human genome editing relates to the impact of the technology on future individuals whose genes are modified without their consent. Clinical ethics accepts the idea that parents are, almost always, the most appropriate surrogate medical decision makers for their children until the children develop their own autonomy and decision-making capacity. This is based on the assumption that, except under rare circumstances, parents have the most to lose or gain from a decision and will ultimately make decisions that reflects the future values and beliefs of their children. According to this assumption, it could be assumed that parents are the most appropriate decision makers for their future children as well. However, there are anecdotal reports of children and adults who disagree with the medical decisions made by a parent during pregnancy or early childhood, such as when death was a possible outcome. There are also published patient stories by individuals who feel that they would not wish to change or remove their own medical condition if given the choice and individuals who disagree with medical decisions made by their parents during childhood.<ref name=":4">{{cite journal | vauthors = Ishii T | title = Potential impact of human mitochondrial replacement on global policy regarding germline gene modification | journal = Reproductive Biomedicine Online | volume = 29 | issue = 2 | pages = 150–5 | date = August 2014 | pmid = 24832374 | doi = 10.1016/j.rbmo.2014.04.001 | doi-access = free | hdl = 2115/56864 | hdl-access = free }}</ref> | One issue related to human genome editing relates to the impact of the technology on future individuals whose genes are modified without their consent. Clinical ethics accepts the idea that parents are, almost always, the most appropriate surrogate medical decision makers for their children until the children develop their own autonomy and decision-making capacity. This is based on the assumption that, except under rare circumstances, parents have the most to lose or gain from a decision and will ultimately make decisions that reflects the future values and beliefs of their children. According to this assumption, it could be assumed that parents are the most appropriate decision makers for their future children as well. However, there are anecdotal reports of children and adults who disagree with the medical decisions made by a parent during pregnancy or early childhood, such as when death was a possible outcome. There are also published patient stories by individuals who feel that they would not wish to change or remove their own medical condition if given the choice and individuals who disagree with medical decisions made by their parents during childhood.<ref name=":4">{{cite journal | vauthors = Ishii T | title = Potential impact of human mitochondrial replacement on global policy regarding germline gene modification | journal = Reproductive Biomedicine Online | volume = 29 | issue = 2 | pages = 150–5 | date = August 2014 | pmid = 24832374 | doi = 10.1016/j.rbmo.2014.04.001 | doi-access = free | hdl = 2115/56864 | hdl-access = free }}</ref> | ||
Other |
Other researchers and philosophers have noted that the issue of the lack of prior consent applies as well to individuals born via traditional sexual reproduction.<ref>{{cite journal |last1=Ranisch |first1=Robert |title=Germline Genome Editing and the Functions of Consent |journal=The American Journal of Bioethics |date=2 December 2017 |volume=17 |issue=12 |pages=27–29 |doi=10.1080/15265161.2017.1388875 |pmid=29148947 |s2cid=10117287 }}</ref><ref>{{cite journal |last1=Vassena |first1=R. |last2=Heindryckx |first2=B. |last3=Peco |first3=R. |last4=Pennings |first4=G. |last5=Raya |first5=A. |last6=Sermon |first6=K. |last7=Veiga |first7=A. |title=Genome engineering through CRISPR/Cas9 technology in the human germline and pluripotent stem cells |journal=Human Reproduction Update |date=June 2016 |volume=22 |issue=4 |pages=411–419 |doi=10.1093/humupd/dmw005 |pmid=26932460 |doi-access=free }}</ref> Philosopher ] further argues that “old-fashioned sexual reproduction is itself an untested genetic experiment”, often compromising a child's wellbeing and pro-social capacities even if the child grows in a healthy environment. According to Pearce, “the question of comes down to an analysis of risk-reward ratios – and our basic ethical values, themselves shaped by our evolutionary past.”<ref>{{Cite book|last=Pearce|first=David|title=Can Biotechnology Abolish Suffering?|year=2017|editor-last=Vinding|editor-first=Magnus|chapter=The Reproductive Revolution|asin=B075MV9KS2|author-link=David Pearce (transhumanist)}}</ref> Bioethicist ] in turn proposes the principle of ], according to which “couples (or single reproducers) should select the child, of the possible children they could have, who is expected to have the best life, or at least as good a life as the others, based on the relevant, available information”.<ref>{{cite journal |last1=Savulescu |first1=Julian |title=Procreative Beneficence: Why We Should Select the Best Children |journal=Bioethics |date=October 2001 |volume=15 |issue=5–6 |pages=413–426 |doi=10.1111/1467-8519.00251 |pmid=12058767 }}</ref> Some ethicists argue that the principle of procreative beneficence would justify or even require ] one's children.<ref>{{Cite journal|last=Veit|first=Walter|date=2018|title=Procreative Beneficence and Genetic Enhancement|url=http://www.kriterion-journal-of-philosophy.org/kriterion/issues/Permanent/Kriterion-veit-01.pdf|journal=KRITERION - Journal of Philosophy|volume=32|pages=75–92|doi=10.1515/krt-2018-320105 |s2cid=149244361 |archive-url=https://web.archive.org/web/20211023193825/http://www.kriterion-journal-of-philosophy.org/kriterion/issues/Permanent/Kriterion-veit-01.pdf|archive-date=October 23, 2021}}</ref><ref>{{cite journal |last1=Daws |first1=Steven |title=Procreative Beneficence in the CRISPR World |journal=Voices in Bioethics |date=6 October 2017 |volume=3 |doi=10.7916/vib.v3i.6031 }}</ref><!-- What about the introduction of parents of "undesirable traits" into their DNA (i.e. by bad habits as smoking, drinking alcohol, excessive eating, lack of exercise. All of these genetic defects thus produced may be inheritable (see epigenetics). Even the choice of the partner influences the genetic makeup in either a good or bad way -see Mendelian laws- (and since most people don't choose a partner based on their genetic makeup (genetic sequencing), this always results in a choice that is not optimal. All of this too is legally allowed, and seemingly uncontroversial. It's not mentioned here yet--> | ||
A relevant issue concerns “off target effects”, large genomes may contain identical or homologous DNA sequences, and the enzyme complex CRISPR/Cas9 may unintentionally cleave these DNA sequences causing mutations that may lead to cell death. The mutations can cause important genes to be turned on or off, such as genetic anti-cancer mechanisms, that could speed up disease exasperation.<ref name=":4" /><ref name=":6">{{Cite book|url= |
A relevant issue concerns “off target effects”, large genomes may contain identical or homologous DNA sequences, and the enzyme complex CRISPR/Cas9 may unintentionally cleave these DNA sequences causing mutations that may lead to cell death. The mutations can cause important genes to be turned on or off, such as genetic anti-cancer mechanisms, that could speed up disease exasperation.<ref name=":4" /><ref name=":6">{{Cite book|url={{google books|plainurl=y|id=XLjJ4AkYWUgC|page=7}}|title=Redesigning Humans: Choosing Our Genes, Changing Our Future|last=Stock|first=Gregory|date=2003|publisher=Houghton Mifflin Harcourt|isbn=978-0618340835}}</ref><ref name=":7">{{cite journal |last1=Wivel |first1=Nelson A. |last2=Walters |first2=LeRoy |title=Germ-Line Gene Modification and Disease Prevention: Some Medical and Ethical Perspectives |journal=Science |date=22 October 1993 |volume=262 |issue=5133 |pages=533–538 |id={{Gale|A14296431}} {{ProQuest|213545041}} |doi=10.1126/science.8211180 |pmid=8211180 |bibcode=1993Sci...262..533W }}</ref><ref name=":8">{{cite journal |last1=Darnovsky |first1=Marcy |title=A slippery slope to human germline modification |journal=Nature |date=July 2013 |volume=499 |issue=7457 |pages=127 |id={{ProQuest|1415758114}} |doi=10.1038/499127a |pmid=23846625 |s2cid=4430248 |doi-access=free |bibcode=2013Natur.499..127D }}</ref><ref>{{Cite journal |last1=Alanis-Lobato |first1=Gregorio |last2=Zohren |first2=Jasmin |last3=McCarthy |first3=Afshan |last4=Fogarty |first4=Norah M. E. |last5=Kubikova |first5=Nada |last6=Hardman |first6=Emily |last7=Greco |first7=Maria |last8=Wells |first8=Dagan |last9=Turner |first9=James M. A. |last10=Niakan |first10=Kathy K. |date=June 2021 |title=Frequent loss of heterozygosity in CRISPR-Cas9–edited early human embryos |journal=Proceedings of the National Academy of Sciences |language=en |volume=118 |issue=22 |pages=e2004832117 |doi=10.1073/pnas.2004832117 |issn=0027-8424 |pmc=8179174 |pmid=34050011|doi-access=free |bibcode=2021PNAS..11804832A }}</ref> | ||
=== Unequal distribution of benefits === | === Unequal distribution of benefits === |
Latest revision as of 10:02, 2 December 2024
Process of editing the human genome so that the changes are inheritedThis article's lead section may be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. (August 2023) |
Human germline engineering (HGE) is the process by which the genome of an individual is modified in such a way that the change is heritable. This is achieved by altering the genes of the germ cells, which mature into eggs and sperm. For safety, ethical, and social reasons, the scientific community and the public have concluded that germline editing for reproduction is inappropriate. HGE is prohibited by law in more than 70 countries and by a binding international treaty of the Council of Europe.
In November 2015, a group of Chinese researchers used CRISPR/Cas9 to edit single-celled, non-viable embryos to assess its effectiveness. This attempt was unsuccessful; only a small fraction of the embryos successfully incorporated the genetic material and many of the embryos contained a large number of random mutations. The non-viable embryos that were used contained an extra set of chromosomes, which may have been problematic. In 2016, a similar study was performed in China on non-viable embryos with extra sets of chromosomes. This study showed similar results to the first; except that no embryos adopted the desired gene.
In November 2018, researcher He Jiankui created the first human babies from genetically edited embryos, known by their pseudonyms, Lulu and Nana. In May 2019, lawyers in China reported that regulations had been drafted that anyone manipulating the human genome would be held responsible for any related adverse consequences.
Techniques
CRISPR-Cas9
Main articles: CRISPR and Cas9The CRISPR-Cas9 system consists of an enzyme called Cas9 and a special piece of guide RNA (gRNA). Cas9 acts as a pair of ‘molecular scissors’ that can cut the DNA at a specific location in the genome so that genes can be added or removed. The guide RNA has complementary bases to those at the target location, so it binds only there. Once bound Cas9 makes a cut across both DNA strands allowing base pairs to inserted/removed. Afterwards, the cell recognizes that the DNA is damaged and tries to repair it.
Although CRISPR/Cas9 can be used in humans, it is more commonly used in other species or cell culture systems, including in experiments to study genes potentially involved in human diseases.
Speculative uses
Genetic engineering is in widespread use, particularly in agriculture. Human germline engineering has two potential applications: prevent genetic disorders from passing to descendants, and to modify traits such as height that are not disease related. For example, the Berlin Patient has a genetic mutation in the CCR5 gene that suppresses the expression of CCR5. This confers innate resistance to HIV. Modifying human embryos to give the CCR5 Δ32 allele protects them from the disease.
An other use would be to cure genetic disorders. In the first study published regarding human germline engineering, the researchers attempted to edit the HBB gene which codes for the human β-globin protein. HBB mutations produce β-thalassaemia, which can be fatal. Genome editing in patients who have these HBB mutations would leave copies of the unmutated gene, effectively curing the disease. If the germline could be edited, this normal copy of the HBB genes could be passed on to future generations.
Designer babies
Main article: Designer babyEugenic modifications to humans yield "designer babies", with deliberately-selected traits, possibly extending to its entire genome. HGE potentially allows for enhancement of these traits. The concept has produced strong objections, particularly among bioethicists.
In a 2019 animal study with Liang Guang small spotted pigs, precise editing of the myostatin signal peptide yielded increased muscle mass. Myostatin is a negative regulator of muscle growth, so by mutating the gene's signal peptide regions could be promoted. One study mutated myostatin genes in 955 embryos at several locations with CRISPR/cas9 and implanted them into five surrogates, resulting in 16 piglets. Only specific mutations to the myostatin signal peptide increased muscle mass, mainly due to an increase in muscle fibers. A similar mice study knoced out the myostatin gene, which also increased their muscle mass. This showed that muscle mass could be increased with germline editing, which is likely applicable to humans because the myostatin gene regulates human muscle growth.
Research
HGE is widely debated, and more than 40 countries formally outlaw it. No legislation explicitly prohibits germline engineering in the United States. The Consolidated Appropriation Act of 2016 bans the use of US FDA funds to engage in human germline modification research. In April 2015, a research team published an unsuccessful experiment in which they used CRISPR to edit a gene that is associated with blood disease in non-living human embryos.
researchers using CRISPR/Cas9 have run into issues when it comes to mammals due to their complex diploid cells. Studies in microorganisms have examined loss of function genetic screening. Some studies used mice as a subject. Because RNA processes differ between bacteria and mammalian cells, researchers have had difficulties coding for mRNA's translated data without RNA interference. Studies have successfully used a Cas9 nuclease with a single guide RNA to allow for larger knockout regions in mice.
Lack of international regulation
The lack of international regulation led researchers to attempt to create an international framework of ethical guidelines. The framework lacks the requisite international treaties for enforcement. At the first International Summit on Human Gene Editing in December 2015 researchers issued the first international guidelines. These guidelines allowed pre-clinical research into gene editing in human cells as long as the embryos were not used to implant pregnancy. Genetic alteration of somatic cells for therapeutic proposes was considered ethically acceptable in part because somatic cells cannot pass modifications to subsequent generations. However the lack of consensus and the risks of inaccurate editing led the conference to call for restraint on germline modifications.
On March 13, 2019 researchers Eric Lander, Françoise Baylis, Feng Zhang, Emmanuelle Charpentier, Paul Bergfrom and others called for a framework that did not foreclose any outcome, but included a voluntary pledge and a call for a coordinating body to monitor the HGE moratorium with an attempt to reach social consensus before furthering research. The World Health Organization announced on December 18, 2018 plans to convene an intentional committee on the topic.
He Jiankui
This section is an excerpt from He Jiankui genome editing incident.The He Jiankui genome editing incident is a scientific and bioethical controversy concerning the use of genome editing following its first use on humans by Chinese scientist He Jiankui, who edited the genomes of human embryos in 2018. He became widely known on 26 November 2018 after he announced that he had created the first human genetically edited babies. He was listed in Time magazine's 100 most influential people of 2019. The affair led to ethical and legal controversies, resulting in the indictment of He and two of his collaborators, Zhang Renli and Qin Jinzhou. He eventually received widespread international condemnation.
He Jiankui, working at the Southern University of Science and Technology (SUSTech) in Shenzhen, China, started a project to help people with HIV-related fertility problems, specifically involving HIV-positive fathers and HIV-negative mothers. The subjects were offered standard in vitro fertilisation services and in addition, use of CRISPR gene editing (CRISPR/Cas9), a technology for modifying DNA. The embryos' genomes were edited to remove the CCR5 gene in an attempt to confer genetic resistance to HIV. The clinical project was conducted secretly until 25 November 2018, when MIT Technology Review broke the story of the human experiment based on information from the Chinese clinical trials registry. Compelled by the situation, he immediately announced the birth of genome-edited babies in a series of five YouTube videos the same day. The first babies, known by their pseudonyms Lulu (Chinese: 露露) and Nana (娜娜), are twin girls born in October 2018, and the second birth or the third baby born was in 2019, named Amy. He reported that the babies were born healthy.
His actions received widespread criticism, and included concern for the girls' well-being. After his presentation on the research at the Second International Summit on Human Genome Editing at the University of Hong Kong on 28 November 2018, Chinese authorities suspended his research activities the following day. On 30 December 2019, a Chinese district court found He Jiankui guilty of illegal practice of medicine, sentencing him to three years in prison with a fine of 3 million yuan. Zhang Renli and Qin Jinzhou received an 18-month prison sentence and a 500,000-yuan fine, and were banned from working in assisted reproductive technology for life.
He Jiankui has been variously referred to as a "rogue scientist", "China's Dr Frankenstein", and a "mad genius". The impact of human gene editing on resistance to HIV infection and other body functions in experimental infants remains controversial. The World Health Organization has issued three reports on the guidelines of human genome editing since 2019, and the Chinese government has prepared regulations since May 2019. In 2020, the National People's Congress of China passed Civil Code and an amendment to Criminal Law that prohibit human gene editing and cloning with no exceptions; according to the Criminal Law, violators will be held criminally liable, with a maximum sentence of seven years in prison in serious cases.Major studies
- The first known HGE research was by Chinese researchers in April 2015 in Protein and Cell. The researchers used tripronuclear (3PN) zygotes fertilized by two sperm and therefore non-viable, to investigate CRISPR/Cas9-mediated gene editing in human cells. The researchers found that while CRISPR/Cas9 could effectively cleave the β-globin gene (HBB), the efficiency of homologous recombination directed repair of CRISPR/Cas9 was inefficient and failed in a majority of trials. Problems arose such as off-target cleavage and the competitive recombination of the endogenous delta-globin with CRISPR/Cas9 led to unexpected mutation. The study results indicated that HBB repair in the embryos occurred preferentially through alternative pathways. In the end only 4 of the 54 zygotes carried the intended genetic information, and even then the successfully edited embryos were mosaics containing the preferential genetic code and the mutation.
- In March 2017, researchers claimed to have successfully edited three viable human embryos. The study showed that CRISPR/Cas9 is could effectively be used as a gene-editing tool in human 2PN zygotes, which could potentially lead to a viable pregnancy. The researchers used injection of Cas9 protein complexed with the relevant sgRNAs and homology donors into human embryos. The researchers found homologous recombination-mediated alteration in CRISPR/Cas9 and G6PD. The researchers also noted the limitations of their study and called for further research.
- An August 2017 study reported the successful use of CRISPR to edit out a mutation responsible for congenital heart disease. The study looked at heterozygous MYBPC3 mutation in human embryos. The study claimed precise CRISPR/Cas9 and homology-directed repair response with high accuracy and precision. By modifying the cell cycle stage at which the DSB was induced, they were able to avoid mosaicism in cleaving embryos, prominent in earlier studies, and achieve a large percentage of homozygous embryos carrying the wild-type MYBPC3 gene without evidence of unintended mutations. The researchers concluded that the technique may be used to correct mutations in human embryos. The claims of this study were however pushed back on by critics who argued the evidence was unpersuasive.
- A June 2018 study researchers reported a potential link for edited cells having increased cancerous potential. The study reported that CRISPR/Cas9 induced DNA damage response and stopped the cell cycle. The study was conducted in human retinal pigment epithelial cells, and the use of CRISPR led to a selection against cells with a functional p53 pathway. The study concluded that p53 inhibition might increase HGE efficiency and that p53 function would need to be watched when developing CRISPR/Cas9 based therapy.
- A November 2018 study of using CRISPR/Cas9 to correct a single mistaken amino acid in 16 out of 18 attempts in a human embryo. The unusual level of precision was achieved with a base editor (BE) system that was constructed by fusing the deaminase to the dCas9 protein. The BE system efficiently edited the targeted C to T or G to A without the use of a donor and without DBS formation. The study focused on the FBN1 mutation that is causative for Marfan syndrome. The study supported the corrective value of gene therapy for the FBN1 mutation in both somatic and germline cells.
Ethical and moral debates
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As early in the history of biotechnology as 1990, there have been researchers opposed to attempts to modify the human germline using these new tools, and such concerns have continued as technology progressed. In March 2015, with the advent of new techniques like CRISPR, researchers urged a worldwide moratorium on clinical use of gene editing technologies to edit the human genome in a way that can be inherited. In April 2015, researchers reported results of basic research to edit the DNA of non-viable human embryos using CRISPR, creating controversy.
A committee of the American National Academy of Sciences and National Academy of Medicine gave support to human genome editing in 2017 once answers have been found to safety and efficiency problems "but only for serious conditions under stringent oversight." The American Medical Association's Council on Ethical and Judicial Affairs stated that "genetic interventions to enhance traits should be considered permissible only in severely restricted situations: (1) clear and meaningful benefits to the fetus or child; (2) no trade-off with other characteristics or traits; and (3) equal access to the genetic technology, irrespective of income or other socioeconomic characteristics."
Several religious positions have been published with regards to human germline engineering. According to them, many see germline modification as being more moral than the alternative, which would be either discarding of the embryo, or birth of a diseased human. The main conditions when it comes to whether or not it is morally and ethically acceptable lie within the intent of the modification, and the conditions in which the engineering is done.
Ethical claims about germline engineering include beliefs that every fetus has a right to remain genetically unmodified, that parents hold the right to genetically modify their offspring, and that every child has the right to be born free of preventable diseases. For parents, genetic engineering could be seen as another child enhancement technique to add to diet, exercise, education, training, cosmetics, and plastic surgery. Another theorist claims that moral concerns limit but do not prohibit germline engineering.
Consent
One issue related to human genome editing relates to the impact of the technology on future individuals whose genes are modified without their consent. Clinical ethics accepts the idea that parents are, almost always, the most appropriate surrogate medical decision makers for their children until the children develop their own autonomy and decision-making capacity. This is based on the assumption that, except under rare circumstances, parents have the most to lose or gain from a decision and will ultimately make decisions that reflects the future values and beliefs of their children. According to this assumption, it could be assumed that parents are the most appropriate decision makers for their future children as well. However, there are anecdotal reports of children and adults who disagree with the medical decisions made by a parent during pregnancy or early childhood, such as when death was a possible outcome. There are also published patient stories by individuals who feel that they would not wish to change or remove their own medical condition if given the choice and individuals who disagree with medical decisions made by their parents during childhood.
Other researchers and philosophers have noted that the issue of the lack of prior consent applies as well to individuals born via traditional sexual reproduction. Philosopher David Pearce further argues that “old-fashioned sexual reproduction is itself an untested genetic experiment”, often compromising a child's wellbeing and pro-social capacities even if the child grows in a healthy environment. According to Pearce, “the question of comes down to an analysis of risk-reward ratios – and our basic ethical values, themselves shaped by our evolutionary past.” Bioethicist Julian Savulescu in turn proposes the principle of procreative beneficence, according to which “couples (or single reproducers) should select the child, of the possible children they could have, who is expected to have the best life, or at least as good a life as the others, based on the relevant, available information”. Some ethicists argue that the principle of procreative beneficence would justify or even require genetically enhancing one's children.
A relevant issue concerns “off target effects”, large genomes may contain identical or homologous DNA sequences, and the enzyme complex CRISPR/Cas9 may unintentionally cleave these DNA sequences causing mutations that may lead to cell death. The mutations can cause important genes to be turned on or off, such as genetic anti-cancer mechanisms, that could speed up disease exasperation.
Unequal distribution of benefits
The other ethical concern is the potential for “designer babies”, or the creation of humans with "perfect", or "desirable" traits. There is a debate as to if this is morally acceptable as well. Such debate ranges from the ethical obligation to use safe and efficient technology to prevent disease to seeing some actual benefit in genetic disabilities.
There are concerns that the introduction of desirable traits in a certain part of the population (instead of the entire population) could cause economic inequalities (“positional” good). However, this is not the case if a same desirable trait would be introduced over the entire population (similar to vaccines).
Another ethical concern pertains to potential unequal distribution of benefits, even in the case of genome editing being inexpensive. For example, corporations may be able to take unfair advantage of patent law or other ways of restricting access to genome editing and thereby may increase the inequalities. There are already disputes in the courts where CRISPR-Cas9 patents and access issues are being negotiated.
Therapeutic and non-therapeutic use
There remains debate on if the permissibility of human germline engineering for reproduction is dependent on the use, being either a therapeutic or non-therapeutic application. In a survey by the UK's Royal Society, 76% of participants in the UK supported therapeutic human germline engineering to prevent or correct disease, however for non-therapeutic edits such as enhancing intelligence or altering eye or hair color in embryos, there was only 40% and 31% support, respectively. There was a similar result in a study at the University of Bogota, Colombia, where students as well as professors generally agreed that therapeutic genome editing is acceptable, while non-therapeutic genome editing is not.
There is also debate on if there can be a defined distinction between therapeutic and non-therapeutic germline editing. An example would be if two embryos are predicted to grow up to be very short in height. Boy 1 will be short because of a mutation in his Human Growth Hormone gene, while boy 2 will be short because his parents are very short. Editing the embryo of boy 1 to make him of average height would be a therapeutic germline edit, while editing the embryo of boy 2 to be of average height would be a non-therapeutic germline edit. In both cases with no editing of the boys' genomes they would both grow up to be very short, which would decrease their wellbeing in life. Likewise editing both of the boys' genomes would allow them to grow up to be of average height. In this scenario, editing for the same phenotype for being of average height falls under both therapeutic and non-therapeutic germline engineering.
Current global policy
There is distinction in some country policies, including but not limited to official regulation and legislation, between human germline engineering for reproductive use and for laboratory research. As of October 2020, there are 96 countries that have policies involving the use of germline engineering in human cells.
Reproductive use
Reproductive use of human germline engineering involves implanting the edited embryo to be born. 70 countries currently explicitly prohibit the use of human germline engineering for use in reproduction, while 5 countries prohibit it for reproduction with exceptions. No countries permit the use of human germline engineering for reproduction.
Countries that explicitly prohibit any use of human germline engineering for reproduction are: Albania, Argentina, Australia, Austria, Bahrain, Belarus, Benin, Bosnia and Herzegovina, Brazil, Bulgaria, Burundi, Canada, Chile, China, Congo, Costa Rica, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, Iceland, India, Iran, Ireland, Israel, Japan, Kenya, Latvia, Lebanon, Lithuania, Malaysia, Malta, Mexico, Moldova, Montenegro, Netherlands, New Zealand, Nigeria, North Macedonia, Norway, Oman, Pakistan, Poland, Portugal, Qatar, Romania, Russia, San Marino, Saudi Arabia, Serbia, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, Thailand, Tunisia, Turkey, the United Kingdom, the United States, Uruguay, and the Vatican
Countries that explicitly prohibit (with exceptions) the use of human germline engineering for reproduction are: Belgium, Colombia, Italy, Panama, and the United Arab Emirates
Laboratory research
Laboratory research use involves human germline engineering restricted to in vitro use, where edited cells will not be implanted to be born. 19 countries currently explicitly prohibit any use of human germline engineering for in vitro use, while 4 prohibit it with exceptions, and 11 permit it.
Countries that explicitly prohibit any use of germline engineering for in vitro use are: Albania, Austria, Bahrain, Belarus, Brazil, Canada, Costa Rica, Croatia, Germany, Greece, Lebanon, Malaysia, Malta, Pakistan, Saudi Arabia, Sweden, Switzerland, Uruguay, and the Vatican
Countries that explicitly prohibit (with exceptions) the use of germline engineering for in vitro use are: Colombia, Finland, Italy, and Panama
Countries that explicitly permit the use of germline engineering for in vitro use are: Burundi, China, Congo, India, Iran, Ireland, Japan, Norway, Thailand, the United Kingdom, and the United States
See also
- Human genetic engineering
- Gene therapy
- Germinal choice technology
- Human genetic enhancement
- CRISPR
- Designer Baby
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Further reading
- Enriquez, Juan; Gullans, Steve (2015). Evolving Ourselves: How Unnatural Selection is Changing Life on Earth. One World Publications. ISBN 978-1780748412.
- Metzl, Jamie (2020). Hacking Darwin: Genetic Engineering and the Future of Humanity. Naperville, IL: Sourcebooks.
- "Special Issue: Human Germline Editing". Bioethics. 34 (1). 2020.
- Venter, Craig (2014). Life at the Speed of Light: From the Double Helix to the Dawn of Digital Life. United Kingdom: Penguin Books. ISBN 978-0143125907.