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Downloaded from genome modification in fertilized animal eggs or embryos, thereby altering the genetic makeup of every differentiated cell in an organism and so ensuring that the changes will be passed on to the organism’s progeny. Humans are no exception—changes to the human germ line could be made using this simple and widely available technology.

MOVING FORWARD. Given these rapid developments, it would be wise to begin a discussion that bridges the research community, relevant industries, medical centers, regulatory bodies, and the public to explore responsible uses of this technology. To initiate this conversation, developers and users of the CRISPR-Cas9 technology, and experts in genetics, law, and bioethics, discussed the implications and rapid expansion of the genome engineering field (1). This group, all from the United States, and which included some of the leaders in the original 1970s discussions about recombinant DNA research at Asilomar and elsewhere, focused on the issue of human germline engineering, as the methods have already been demonstrated in mice (6) and monkeys (7). The Napa discussion did not address mitochondrial transfer (8, 9), a