Genetics plays a major role in autism, but scientists are also investigating the potential role of environmental factors such as parental age, premature birth and prenatal exposure to drugs, environmental chemicals or infections. The idea that something that occurs during pregnancy may influence neurodevelopment isn't a particularly new or crazy or outlandish idea, said Renee Gardner, an associate professor of epidemiology at Sweden's Karolinska Institute. We know there's a large heritable or familial influence, but environment interacts with genetic tendencies.