What are the causes of autism?

The cause for autism is currently unknown. It is clear that autism has a genetic component and tends to run in families. [4] It is likely that both genetic and environmental factors have a role in causing autism. Possible causes of autism include:
  • complex genetic abnormalities [8-10]
  • altered levels of chemical signals in the womb [6]
  • problems with movement of nerve cells in the brain during early brain development [7]
  • problems with closure of the neural tube (an early developmental structure related to the spinal cord) [12]
  • exposure to certain medications associated with birth defects in the womb, such as thalidomide and valproic acid [Rodier and Hyman, 1998] [11]
  • environmental exposures, sometimes even at low levels which do not produce abnormalities in other individuals
  • limited ability to detoxify environmental exposures, even at low levels
Although one study suggested that the measles, mumps, and rubella vaccine may be linked with autism [16], the weight of the evidence argues against this possibility. [17-19]