I reject the notion that either transsexualism (TS) or transgender (TG including CDs) are disorders. I believe they are rather common variants in early human development. They indicate to me that the person began life as a set of boy-girl twins who merged together to form a viable embryo.
This is commonly known as a chimera. Chimeras were thought to be extremely rare, but advances in the understanding of embryology have revealed that most likely one out of every eight pregnancies begin as twins and end up as a single embryo. Many of these twin sets are boy-girl pairs and their merging is highly correlated with the proclivity towards gender variant behavior.
The reason is because the hypothalamus-pituitary-gonad (HPG) axis is hybridized -- both male and female. Remember the studies conducted that revealed the number of neurons in the bed nucleus of the stria terminalis (BSTc) of male-to-female TS was similar to that of the females? The Stria Terminalis is a component of the HPG axis and hybridization is likely the reason why it presents with female neuron numbers in transsexual women. If the Stria Terminalis in these subjects were tested using the right methods, the tests would likely reveal these regions were actually of comprised different genetic material than the hosts.
I believe TS & TG folk share in common this biological variant in human development (i.e. a proclivity towards cross gender expression). We are *all trans women* and the differences we see in development (i.e. older vs younger transitioners) has more to do with whether the individual in question was born straight or born gay....
One who is born straight holds tight to her gender role ...and represses the feminine within herself because she wants to succeed as a woman-loving male. The feminine may become exotic to her and later, erotic. Finally after years, she transitions or comes to peace with being bi-gendered.
One who is born gay will not hold onto her gender role as tightly because she doesn't have the drive to succeed as a woman loving male. So she naturally embraces the feminine inside her at an early age and it becomes part of her identity instead of an "exotic thing" that must be kept at bay. And so the realization that she wants to transition comes much much earlier.