We do not know all of the causes of ASDs. However, we have learned that there are likely many causes for multiple types of ASDs. There may be many different factors that make a child more likely to have an ASD, including environmental, biologic and genetic factors

• Most scientists agree that genes are one of the risk factors that can make a person more likely to develop an ASD.
• Children who have a sibling or parent with an ASD are at a higher risk of also having an ASD.
• ASDs tend to occur more often in people who have certain other medical conditions. About 10% of children with an ASD have an identifiable genetic disorder, such as Fragile X syndrome, tuberous sclerosis, Down syndrome and other chromosomal disorders.
• Some harmful drugs taken during pregnancy have been linked with a higher risk of ASDs, for example, the prescription drugs thalidomide and valproic acid.
• We know that the once common belief that poor parenting practices cause ASDs is not true.
• There is some evidence that the critical period for developing ASDs occurs before birth. However, concerns about Vaccines and infections have led researchers to consider risk factors before and after birth.