Supposedly, it's a mutation that gives you purple eyes at puberty, no hair, and for women, fertility without menstruations.
The origins appear to be invented in some fan fiction. There's no reference to it in Google Scholar, which covers abstracts from a huge number of scientific papers.
Cameron Miquelon claims to be the original author in about 1998, and is frustrated by people who can't tell the difference between fiction and fact:
Alas, what’s truly astonishing is that in spite of this post’s existence (as well as the true origin of Alexandria’s Genesis being a Daria fan fiction website), nothing has changed among the 99 percent of you who believe that what I wrote is truth, if my bookmarked Tumblr search tag is anything to go by.
For that, I hate you all so very much.
Anyway, there you have it: Alexandria’s Genesis is simply a bad mashup of Daria, Art Bell, Twilight, witchcraft and Cylon skinjobs adopted by New Agers and others who should know better, but don’t and won’t.