However, germ-line modification is not the only way to avoid inheritance of a Huntington’s gene; there are embryo-selection methods that achieve the same end. In fact, only in rare circumstances are germ-line alterations the only way to achieve avoidance of passing on a deleterious gene.

The other, more unsettling kind of germ-line modification would involve attempts to modify inheritance for the purpose of enhancing an offspring’s physical characteristics or intellectual capability. We can call this voluntary modification in that there is no compelling medical need. Choosing to transmit voluntary changes to future generations involves a value judgment on the part of parents, a judgment that future generations might view differently.

This can be seen as eugenics, thought by earlier generations to be desirable but now generally considered abhorrent. Also, we often do not know well enough the total range of consequences of a given gene alteration, potentially creating unexpected physiological alterations that would extend down through generations to come. For these reasons and others, voluntary genome alteration might well be outlawed, at least at the present stage of knowledge.