UCLA researchers found a genetic link (evidentiary) that ties TS to genetics. Their research has been duplicated giving it some validity but still no definitive beyond doubt tie. Regardless, the evidence of genetic ties is extremely good.
That said, there has been no direct ties to heredity. It is hit and miss.
Some of the current thinking is that it is a combination of prenatal hormone release that causes the genetic factor. Again unproven except for the genetic link evidence. Maybe someday they will figure it out. I hope they dont.
Kimberley