Children whose older sisters are on the spectrum are at higher risk for autism than are those with affected older brothers, a new study suggests. Younger brothers of children with autism are at greater risk than younger sisters.

The genetic makeup of an individual plays much a bigger role than environmental factors in whether he or she develops autism, according to one of the largest twin studies to date.

A 20-minute test enlists parents in gauging a toddler’s social development by showing them a video of how a typically developing child acts.

Restricted behaviors in autism represent a genetic link with inattention and hyperactivity in attention deficit hyperactivity disorder, say Tinca Polderman and Henrik Larsson.

The genetic and environmental factors that underlie difficulties with language differ from those that influence other autism traits, according to a new study of more than 3,000 twin pairs. The study, published 2 August in the American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, suggests that difficulty with language is not a core symptom of autism.

Common genetic variants that have minor effects may contribute about half the risk of developing autism, according to a study published Sunday in Nature Genetics. Identifying these variants would require tens of thousands of samples.

Having one child with autism raises the odds of having a second child with the disorder 20-fold, according to one of the largest epidemiological studies so far to address the inheritance of autism risk.

Children with autism have atypical patterns of epigenetic modifications — chemical tags on DNA that influence gene expression, suggests a study published 29 May in PLOS Genetics.

If inherited risk for autism is 50 percent, does that make the remaining half of risk environmental? Scientists clarify a large population study.

A large study of autism in Swedish families suggests that about half of the risk for autism comes from genetics and the other half from environmental factors, researchers reported 7 May in The Journal of the American Medical Association. However, the mathematical model the study used may not be appropriate for evaluating autism risk, experts say.