Homosexuality is also rampant in the animal kingdom, even among creatures to which we ascribe very little in the way of "choice" in their actions. Certainly the animals aren't picking sex partners with a knowledge of the Bible's teachings. It's instinct in some form. I think we can agree on that.
So it's very common in nature, which would make it "natural" by definition.
We don't have to know the exact gene to observe and understand this.
Although I do agree some people are born with homosexual feelings (acting on those feelings seems to be the issue of the discussion), I don't know think the animal kingdom should be the source of whether something is "natural" or not. If an animal is cannibalistic does that mean that cannibalism is natural?
Does that mean if an animal does this
(insert action) then it is "natural" for a human to do so too?
Some animals do some weird stuff? But then again so do some humans...