You're right, as I posted earlier, (03/11 at 0.30), Oneflewover. There's hardly any being done because researchers don't want anything to do with such a volatile and vengeful group. Since Blanchard and Bailey (and, to a lesser extent, Dreger) everyone knows that if there's any chance TRAs won't greet your findings with delight you'd be best avoiding this group at all costs.
LGBT groups in the US are using questionnaires, which are self-selecting, unverified and designed to produce a desired result. It's not always impossible to examine what's known. TRAs make preposterous claims about the murder, suicide rate and lifespan of transwomen, and these can be disproved.
Medicine and science are affected by fashion and politics. Transgenderism is so much affected that research has come to a standstill in the USA, thought the Tavistock is presumably doing lots here. I imagine it helps if all or nearly all the patients are using the same health system, as in here and in Sweden.