I don't know much about such things but it doesn't seem fair to compare people born with a medical condition to people who engage in bizarre deviant sex.
Hence the "gene pool" remark. Seems to me if one comes from corrupted genes, this kind of thing can happen. It is they who wish to include this particular malady with their "victim" status.
Same kind of things happens in nature when the gene pool gets to shallow. Diversity is a
good thing. It promotes the most advantageous traits into the future generations.
Somehow I think having birth defects promotes the opposite and is usually brought about by inbreeding or exposure to damaging environments, at least in nature, that is. As I have no idea what specific circumstances brought about any certain individuals plight, it would be impossible to point out any one thing, however, genetics is my best guess.