Autism spectrum disorder
how child gets it
Children who have a sibling with ASD are at a higher risk of also having ASD.
Children born to older parents are at greater risk for having ASD.
ASD tends to occur more often in people who have certain genetic or chromosomal conditions, such as fragile X syndrome(http://www.cdc.gov/ncbddd/fxs/facts.html) or tuberous sclerosis.