Researchers have used CRISPR in cells from human, plants and animals; in fact, CRISPR has worked in all species examined to date. Notably, the CRISPR technology has been used to reverse symptoms in an adult mouse with a liver disorder and to alter DNA in non-human primates — important steps towards developing new gene therapies in humans. While genetic changes introduced into a liver cell will not be inherited in the genome of any of the individual’s future offspring, DNA alterations that are introduced in the cells that will become egg or sperm, or the cells in early stage embryos, can be passed on to future generations. This is known as germline editing, and its prospects have led to discussion and debate worldwide about whether germline genetic modification in humans is appropriate, and whether or how society should proceed with such research and possible application.

On one hand, critics emphasize both the technical and ethical issues with making changes to the genome that can be passed down to offspring. There are concerns that any unforeseen effect in the editing process can become inherited. Other questions are being asked — do we have the right to alter the genome of our future generations? Would the editing of certain diseases or disabilities lead to stigmatization of people who are living with those conditions? And who gets to decide what are considered diseases or disabilities that should be edited? At the same time, proponents argue that germline modification can potentially eliminate diseases such as Huntington’s disease, a debilitating neurological condition caused by a single gene variant. They also argue that humans have long been altering the lives and genetics of our offspring without their explicit consent, through procedures such as genetic counseling and preimplantation genetic diagnosis.

In December 2015, the US National Academies, the UK Royal Academy, and the Chinese Academy of Sciences convened scientists, social scientists, ethicists, and other stakeholders for an International Summit on Human Gene Editing in Washington, DC. A statement released at the end of the summit emphasized that it would be “irresponsible” at this time to proceed with the clinical use of germline editing, but did not recommend banning the technique, instead suggesting that research should continue. In February 2017, the US National Academies’ expert committee on human genome editing released its report, recommending that research on, and use of, somatic genome editing for medical treatment should continue under the existing regulatory framework, but that there should be “broad public input” before expanding the technology’s application to “genetic enhancement.” At the same time, the report recommends that clinical trials for germline genome editing to treat “serious diseases or disabilities” should proceed only after much more research, and only when stringent technical and ethical criteria are satisfied. Going forward, the report emphasizes the need for continued public engagement and policy debate.

Currently, germline genetic modification is illegal in many European countries and in Canada, and federal funding in the United States cannot be used for such work. As of January 2017, researchers in the UK, Sweden and China have received approval to perform gene editing in human embryos for research purposes only (in addition, existing laws or guidelines in these countries only allow research on embryos up to 14 days after fertilization).

In November 2018, news reports emerged that the first children whose genomes were edited with CRISPR during their embryonic stage, a pair of twins, have been born in China. While the claims have still not been independently validated or published in peer-reviewed journals, the claims have drawn significant controversy. In 2019, scientists, ethicists and the broader society continue to debate the path forward.