Inheritable genetic modification (IGM, also called germline engineering) means changing the genes passed on to future generations. The genetic changes would be made in eggs, sperm or early embryos; modified genes would appear not only in the person who developed from that gamete or embryo, but also in all succeeding generations. IGM has not been tried in humans. It would be by far the most consequential type of genetic modification as it would open the door to irreversibly altering the human species.
DNA Editing in Mouse Embryos Prevents Disease[Quotes CGS's Marcy Darnovsky]by Sara Reardon, Nature NewsApril 23rd, 2015“It is a bit of a slippery slope — if you start allowing any editing tool, you open a Pandora’s box of the possibility to edit anything.”