http://bostonglobe.com/metro/2011/12/11/led-child-who-simply...

This is a good article on a family in Maine that are dealing with a transgender kid who is part of a set of identical twins. One is a son, the other a daughter, but biologically/genetically should be about the same.

It would be interesting to see the results of a genetic study and fMRI scan on the two of them. I think it is studies of identical twoins that would be most useful to learn about the sources of being TS, eh?