The genetic components of transsexualism came out late this year, 2008:
IN THE largest ever genetic study of transsexuals, Australian researchers have discovered a DNA variation linked to male-to-female transsexualism.
The research confirmed that transsexuality was not a lifestyle decision, as some had suggested, said another team member, Trudy Kennedy, the director of the Monash Gender Dysphoria Clinic in Melbourne.
A gene variant has been identified that appears to be associated with female-to-male transsexuality - the feeling some women have that they belong to the opposite sex.
"This is in line with what we previously know about masculinisation of the brain and is therefore less likely to be a chance finding", he says. "Hence, the study is important and adds to the notion that gender identity is influenced by sex hormones early in life, and that certain gene combinations make individuals more vulnerable to aberrant effects."
Brain May 'Hard-Wire' Sexuality Before Birth.
“Our findings may explain why we feel male or female, regardless of our actual anatomy,” Vilain said. “These discoveries lend credence to the idea that being transgender — feeling that one has been born into the body of the wrong sex — is a state of mind.
Male-to-Female Transsexuals Have Female Neuron Numbers in a Limbic Nucleus.
The number of neurons in the BSTc of male-to-female transsexuals was similar to that of the females (P = 0.83). In contrast, the neuron number of a female-to-male transsexual was found to be in the male range. Hormone treatment or sex hormone level variations in adulthood did not seem to have influenced BSTc neuron numbers. The present findings of somatostatin neuronal sex differences in the BSTc and its sex reversal in the transsexual brain clearly support the paradigm that in transsexuals sexual differentiation of the brain and genitals may go into opposite directions and point to a neurobiological basis of gender identity disorder.