It's a really interesting question, but I'm not sure it's possible to say there is a genetic component.
Statistically speaking even with a random distribution, there are going to be familial clusters, as well as families that legitimately do not have anyone in them on the trans spectrum (by legitimately, not just closeted I mean). Unfortunately, real data just doesn't exist to draw any meaningful correlation, much less causation. Anecdotally, I've seen a number of people say it "runs in the family", but we are an impartial sample to begin with, and even then it has only been a handful of people on this site versus thousands that make no mention of it or say they are the only one (or at most it's like them and a third cousin).
When it comes down to it, the question of there being a sort of trans gene is really tricky, and some people welcome the idea while other people find it insulting. Personally, and entirely unscientifically, I think it is likely that there are cases where familial genetics cause a predisposition towards being trans, but they are most likely exceedingly rare and in most examples it is just purely random distribution clustering than some strong genetic trait. (I would also hesitantly draw a line on this issue between the more traditional view of being trans and modern social evolution with many people in the current generation. In the case of the latter, there would a high level of clustering due to environment as with any social movement, which does not de-legitimize their being trans at all but does mean the clustering in those cases is not indicative of genetic clustering with the past definitions that did not share that social component.)