Around 30 nations worldwide, including the United States, already have laws to directly or indirectly ban the clinical use of germline editing. CRISPR research on embryos is currently banned from receiving federal funding, but can be conducted using private funding. The Food and Drug Administration prohibits gene modification on viable human embryos, which means any genetically modified human embryos must be destroyed, rather than brought to term.
The scientists called for a fixed period – perhaps five years – when no clinical uses of germline editing are allowed worldwide.
"As well as allowing for discussions about the technical, scientific, medical, societal, ethical and moral issues that must be considered before germline editing is permitted, this period would provide time to establish an international framework," they wrote.
The scientists noted that here is broad scientific consensus that germline editing is not yet safe or effective enough to be considered for clinical use. They also highlighted the distinction between "genetic correction," which involves working to edit out rare mutations, and "genetic enhancement," or the attempt to improve human individuals and the species.
The Nature scientists noted that even efforts at genetic correction, when undertaken in order to cure a disease, can have unintended consequences. For example, a common variant of the gene SLC39A8 decreases a person's risk of developing hypertension and Parkinson's disease, but increases their risk of developing schizophrenia, Crohn's disease, and obesity.
This is also true for the genes that He worked with in his research, as altering those genes could make the genetically modified babies more susceptible to certain viral infections.
"Its influence on many other diseases – and its interactions with other genes and with the environment – remains unknown," the scientists wrote.
"It will be much harder to predict the effects of completely new genetic instructions – let alone how multiple modifications will interact when they co-occur in future generations. Attempting to reshape the species on the basis of our current state of knowledge would be hubris."
In Dignitas personae, its 2008 instruction on certain bioethical questions, the Congregation for the Doctrine of the Faith said that while somatic cell gene therapy is in principle morally licit, "because the risks connected to [germ line cell therapy] are considerable and as yet not fully controllable, in the present state of research, it is not morally permissible to act in a way that may cause possible harm to the resulting progeny."
The instruction also warned against a "eugenic mentality" that aims to improve the gene pool, adding that there could be social stigmas and privileges applied to people with certain genetic qualities, when "such qualities do not constitute what is specifically human."
CNA spoke to John DiCamillo, an ethicist at the National Catholic Bioethics Center, in early 2017. He explained that somatic cell gene editing may be morally legitimate when used for "a directly therapeutic purpose for a particular patient in question, and if we're sure we're going to limit whatever changes to this person." He pointed to gene therapy trials for disorders such as sickle cell disease and cancer that show promise for treating difficult disorders.
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Editing sperm, eggs, or early embryos, however, presents serious concerns, he said. Manipulating sperm and ova requires removing them from a person's body; if conception is achieved with these cells, it is nearly always through in vitro methods. This practice of in vitro fertilization is held by the Church to be ethically unacceptable because it dissociates procreation from the integrally personal context of the conjugal act.
Scientists at the Charlotte Lozier Institute, the research and education arm of Susan B. Anthony List, reacted to the Nature scientists' proposal by saying their suggested moratorium does not go far enough.
"This proposal for a temporary moratorium on implanting and gestating gene-edited embryos is disappointingly short-sighted," said Dr. David Prentice, CLI's vice president and research director.
"Scientifically unsound and ethically problematic experiments on human embryos, including creating gene-edited embryos in the lab and then destroying them, would still be allowed and even encouraged. We call instead for the full prohibition of gene-editing experiments on embryos or germ cells – not just a speed bump."