What exactly do you mean? Are you asking if it's inevitable that someone with the gene will develop autism or if someone is genetically predisposed to developing it? Or are you suggesting that genetics aren't responsible for leading to some people getting skin cancer, being obese, or alcoholic? Maybe because those genetics also involve other factors like sun exposure and lifestyle choices?

I would suppose that the genetics involved in autism cases would be more or less like tay-sachs. Because you would have been born with it.

So unless you are aware of some research that shows a gene linked with autism that doesn't activate without external factors (going out on a limb and guessing vaccines here) then I'd have to stick with the comparison with Tay Sachs.

Curious as to why you're interested in the distinction.