Just read this fascinating article in Science Alert.  They say

“A fresh look at data from earlier research has reaffirmed what many researchers had thought – autism is primarily in the genes.

Other studies have shown autism spectrum disorder (ASD) tends to cluster in families and is associated with particular genes, but nailing down the risks with precision is a complex task. This new research has put a figure on the chances, claiming 83 percent of autism cases are inherited.

The study led by researchers from the Ichan School of Medicine in New York reanalysed a Swedish longitudinal study that involved over 2.6 million pairs of siblings, 37,570 pairs of twins, and just under a million half-sibling pairs.

Of these, 14,516 children had an ASD diagnosis.

Autism and its associated spectrum of conditions is a rather complex disorder, distinguished by difficulties in communicating and engaging in social interactions.

Read more here.