Recent research has linked certain factors associated with air pollution to increased risk of ASD. This study will expand this finding by using prenatal blood obtained through the State of California to identify 1) genetic mutations of the MET receptor and whether these mutations affect the association, and 2) specific immune markers that may also contribute to risk. The researchers will map addresses of mothers to estimate the amount of air pollution they were exposed to while they were pregnant and early in the child’s life. Then, they will also look to see if genes of the mother and the child alter, or change, this risk. This research will study the MET gene, which has been linked with autism in many previous studies. There is evidence from animal data that the way MET works may be influenced by prenatal exposure to air pollution, supporting the biology of this interaction. However, MET also can affect the immune system. Studying how genes and the environment interact can provide important insights into the biology of ASD, making it possible for future research to test early identification or treatment methods. Understanding the role of the immune system in ASD through this interaction may also allow us to target specific environmental contaminants aiding the health of all people.