Why Do More Boys Than Girls Have Autism?

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The field has not really figured out why there's a substantially higher rate in boys. You would think that this would be one of the great biological clues and it hasn't translated into a clear, firm understanding, if genes on X chromosomes are involved and a girl has two X chromosomes and one of them has a gene defect and maybe the idea would be that the other chromosome is relatively protected and then of course, the notion was well, if men only have one X chromosome they have that mutation, well there isn't another X chromosome that the male has, he has a Y chromosome right? So that mutation is there all by itself and there's no additional X chromosome to counter-balance it or pick up the slack.

That model of course is pretty simplistic. It doesn't really match up with what we now know. We now know that there are hundreds if not thousands of genes that may be involved. A small number in each individual, so maybe a small handful, 1 to 5 in some individuals, maybe 5 or 10 or 20 in others, but they are scattered throughout the genome, not just the X chromosome.

So it`s a mistery.