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.
ASDs are an urgent public health concern. Just like the many families affected in some way by ASDs, CDC wants to find out what causes the disorder. Understanding the risk factors that make a person more likely to develop an ASD will help us learn more about the causes. We are currently working on one of the largest U.S. studies to date, called Study to Explore Early Development (SEED). SEED is looking at many possible risk factors for ASDs, including genetic, environmental, pregnancy, and behavioral factors.
Who is Affected
ASDs occur in all racial, ethnic, and socioeconomic groups, but are four times more likely to occur in boys than in girls. CDC estimates that between 1 in 100 and 1 in 300, with an average of 1 in 150, children in the United States have an ASD.
More people than ever before are being diagnosed with an ASD. It is unclear how much of this increase is due to a broader definition of ASDs and better efforts in diagnosis. However, a true increase in the number of people with an ASD cannot be ruled out. We believe the increase in ASD diagnosis is likely due to a combination of these factors.
Within the past decade, CDC’s Autism and Developmental Disabilities Monitoring (ADDM) Network has been estimating the number of people with an ASD in the U.S. We have learned a lot about how many children in the U.S. have an ASD. It will be important to use the same methods to track how the number of people with an ASD is changing over time in order to learn more about the disorders. |
