If GD is a biological thing, then it's nature rather than nurture that has set us the challenges that we face as transgendered individuals.
That said, it's fairly well-documented that birth order has a profound effect on development. I'm interested to know if there is any kind of statistical relationship between birth order and GD. I have never seen anything that says as such, but let's see what we get.
For the record, I'm the youngest of four.