Okay... this psychology degree comes in handy sometimes....
Neurosurgeons may have found that the hypothalamus in MtFs is smaller than in other males, but they also found this in gay males, back in the 1980s. Problem with that study, however, was that they used it to say there was a genetic difference between gay males and straight ones, despite the fact that the brains they dissected to come to this conclusion were all from gay men who died of AIDS. Thus, there was no way of knowing whether they had smaller hypothalami because they were gay, or because of AIDS. There's always 2 sides to every story.
As far as there being psychological causes for TS, it's not likely that it would be a result of primarily genetics. Believe me, being an FtM myself, I'm not about to say we're all crazy, but modern psychologists believe that personality is determined 50% by genes and biology, and 50% by environment. There is a prevailing opinion now that lesbians and FtMs had an overabundance of androgens in utero, which masculinized them without making them genetically male, and vice-versa (gay males and MtFs had too much estrogen in the womb). If this is the case, it's out of our control... but then environment comes in, and either your parents enforce gender norms on you and you become someone who identifies with your biological sex, but is lesbian or simply incredibly depressed, or your folks are more lax and free-thinking, you go through childhood as a tomboy or a "sissy" boy, and eventually realize your TS status.
Regardless of whether or not scientists eventually say that TS is caused by psychological problems from trauma early in life, you are who you are. And if it is the result of early trauma, you have no personal control over it, anyway. Years in therapy could be wasted just to tell you what you already know. I'd say, transition if you feel it's right, don't if you don't, but don't worry about the etiology of your condition. Just be you.
Rafe