Fragile X Syndrome
Fragile X syndrome is the most common known genetic cause of autism and mental retardation in boys, the AAP notes in its report on autism spectrum disorders. Between 30 and 50 percent of people diagnosed with Fragile X demonstrate the characteristics of autism, including impairment in speech and language development and behavioral traits.
The National Fragile X Foundation notes that "the impairment can range from learning disabilities to more severe cognitive or intellectual disabilities (sometimes called mental retardation)." Visit www.fragilex.org for more informaiont about the relationship between autism and Fragile X.