The relative contributions of genetic and environmental factors to autism and traits of the condition have held steady over multiple decades, according to a large twin study 1.
Among tens of thousands of Swedish twins born over the span of 26 years, genetic factors have consistently had a larger impact on the occurrence of autism and autism traits than environmental factors have. The study suggests that genetics account for about 93 percent of the chance that a person has autism, and 61 to 73 percent of the odds she shows autism traits.
Some experts question whether twin studies — even large ones like this — can offer definitive answers.
The origins of autism may involve an interaction between genetics and the environment, which twin studies do not capture, says Brian Lee, associate professor of epidemiology and biostatistics at Drexel University in Philadelphia, Pennsylvania, who was not involved in the study.
“Asking whether genetics or environment is more important is the wrong question,” Lee says. “To me, it’s sort of like asking whether it’s more important to put on your left shoe or your right shoe to go out in public.”