Question: How does a family history of autism affect the risk of my child developing an autism spectrum disorder?
Answer: A family history of autism does slightly increase the risk of having another child with autism. This is greatest when a couple has a child with autism and they're considering having further children. Baby boys are at much greater risk than girls for reasons that we don't fully understand. While the risk of having a child with autism is increased significantly over the general population if there's already one child with autism, it is still far more likely that a subsequent child will not have autism than that they will have autism.
The great majority of families affected by autism have only a single affected child. The risks are lower if there's a more distant relative, such as a cousin or uncle affected with autism.