Intersex is too, according to the Wikipedia *ahem*
Some people lack the enzyme needed to convert testosterone to dihydrotestosterone, which is a cause of 5-alpha-reductase deficiency. Androgen insensitivity syndrome is the most common cause of 46, XY intersex.
Also, as I said before, biologically there are 2/3 genders how you see it, while the rest is basically social identification.