Ahogaday linked a study awhile ago that claimed that, while autism was present in both males and females, testosterone "aggravates" the symptoms.
Obviously, if that's true, then higher levels of testosterone = more severe symptoms. Also, as others have pointed out, men are missing an entire leg of a chromosome, and there are more steps involved in creating males in the womb; therefore, there are more opportunities for things to go awry.
This is one of the reasons I don't complain overmuch about having a period or the possibility of getting pregnant. The male body has a glut of potential problems which makes me grateful for female robustness. 
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"If we fail to anticipate the unforeseen or expect the unexpected in a universe of infinite possibilities, we may find ourselves at the mercy of anyone or anything that cannot be programmed, categorized or easily referenced."
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