Wrong. If there were such a gene in Day 1 of evolution, it would have diluted out by now. Just like you don't see humans who look like primates anymore, because that part of our genetic code was washed out.
A birth defect is a mutation, that's different from an evolutionary gene. A child born with one arm is a mutation, if that one armed child were to grow up and procreate, his offspring has a 99% chance of having both arms because it's not part of his genetic code to have one arm. If you're comparing homosexuality to a
mutation, you are actually proving my point.
And the increase in special needs children comes from humans procreating at an older age than we used to, it has nothing to do with genetics.