"Asperger syndrome is listed as a "rare disease" by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH). This means that Asperger syndrome, or a subtype of Asperger syndrome, affects less than 200,000 people in the US population. "
http://www.rightdiagnosis.com/a/asperge ... /intro.htm
I found another article:
http://www.autism.org.uk/about-autism/s ... rders.aspx