Here's the conclusion of a new study on the causes of autism:
In a cohort of more than 600,000 sibling pairs, the risk of the second child developing autism was significantly higher if there were fewer than 36 months between the pregnancies, according to Keely Cheslack-Postava, PhD, and colleagues at Columbia University in New York City. The highest risk was associated with pregnancies less than a year apart, Cheslack-Postava and colleagues reported in the February issue of Pediatrics.
Hmmm. I was born 32 months after my sister, right on the edge of the danger zone. I wonder if that explains anything?