I would just like to point out for our side the dangers of trying to insist that transsexuality (or homosexuality) is biologically determined.
This may well be the case and some indications point there, but there is no proof yet.
I believe it is better to say that transsexuality (or homosexuality) is a condition of unknown causes,
that can present itself very early in life, that does not respond to coercive therapy and is immutable.
As such, it deserves full protection under the law of any other immutable characteristic.