I have a five year-old who has sensory sensitivities, difficulty with emotional regulation, and has an IEP for social/pragmatic skills. I mention this because we have not had him evaluated for ASD but I know that these traits are often linked with ASD.
He also is somewhat gender non-conforming. From the time he was 2 he had a consistent and abiding passion for stereotypically "girl" interests: princesses, fairies, etc. Whenever he would dress up or roll-play he would be a female character (we have many dresses for costumes at home).
My wife and I have been very supportive of his interests and are letting him take the lead. At the moment he refers to himself as he (he is biologically male), dresses like a boy (though prefers leggings and pastel colors) and does not seem to show any distress with being a boy. I'm mentioning this just to convey that at the moment he's gender non-conforming but doesn't show signs that would more strongly indicate that he's transgender, though we'll continue to see how this evolves.
I guess what I was wondering is: is any relationship between ASD and being gender-nonconforming/transgender or are these best thought of as being separate traits? Of course, not everyone who is one is the other (and vice versa) but are there any relationships that have been reported and if so, are there any theories as to why they might be related?