You'd do well to ask Scripter and/or EdReform about that text. It was likely a fabrication by pro-homosexual text book writers or faux researchers. I have never, ever heard or read that, and if it was really true, it would be blasted all over the place, since homosexual pushers are searching devotedly for anything that proves their points.
Neither have I. And I would agree with you, lj, that it was most likely discredited or initially bogus. The closest thing I can think of was Simon LeVay's hypothalamus study, but LeVay himself admitted his study didn't support what many claim it supported.
Sorry, the text is somewhere in my house, but I'm not going to dig it out. I can tell you that it was written by one of my professors and he was pretty respected. His pursuit was interested in only where scientific evidence led. A real scientist, long gone.
Think about cancer, we think of it as one disease, but its really many. Or alcoholism. Is it a disease with a genetic component? No question. Is it a moral condition that can be avoided by choice? Also a proven.
While I don't want homosexual's pushing their lifestyle and advancing their agenda and for some I think it is an immoral 'choice', I am open to science identifying those people that have a physical (gene) reason for it. Love the sinner, hate the sin, know the Truth.