The impact of hormone therapy, both good & bad on mental function will soon be added.

Gender dysphoria, the mento-emotional component of being trans, involves feelings of low self-esteem, a distorted sense of self, depression, anxiety & obsessionalism.  And it is clearly hormone sensitive. 

Yes, it has clearly been proven to be. 

Some forms of transsexuality are inherited via abnormalities in the power of the androgen receptor gene.

Trans-genderism or transsexuality of the M to F variant does not appear to be linked in any way to sexual orientation. Having said that transsexuality is a mixed bag.

A transgender person is someone who happens to possess the unambiguous reproductive system of one gender, but feels that he or she belongs with the opposite gender. She doesn't choose to be transgendered, the transgender drive chooses her.