While the cause, or causes, of autism spectrum disorders (ASDs) remain elusive, experts believe they have pinpointed factors that may place people more at risk of developing autism.

Genetic Factors

Among other factors, genetics can place an individual at risk for developing some form of autism. If a person has a brother, sister (especially an identical twin), or parent with an ASD, that person is more likely to also have an ASD.

Some medical conditions have been connected to a higher risk of having autism. These include genetic disorders such as Fragile X syndrome and tuberous sclerosis. Though the link between tuberous sclerosis and ASD is unclear, studies have shown that ASD rates are much higher among children with tuberous sclerosis than those who do not have the disease.

Some key risk-related statistics provided by the U.S. Centers for Disease Control and Prevention (CDC) include:

  • If one identical twin has an ASD then there is a 60 to 96 percent chance the other twin will have some sort of ASD.
  • Fraternal twins have a lower chance, but if one has an ASD then the other has up to a 24 percent chance.
  • If a family already has one biological child with autism, there is a two to eight percent chance of the family having another biological child with an ASD.
  • About 10 percent of children who have an ASD also have another genetic, neurological, or metabolic disorder.

Exposure to Certain Drugs

The CDC states that some drugs, like thalidomide and valproic acid, have also been implicated in causing higher risks of ASDs if they are taken while a woman is pregnant.

Environmental Factors

Exposure to heavy metals and other toxins in the environment is also suspected of increasing the risk of ASDs.