A systematic review of parent-infant interaction in infants at risk of autism.

Wan et al. (2019) pooled every paper that filmed babies and parents together. They kept only studies with infants who had an older brother or sister with autism. These babies are called "infant siblings" and have a higher chance of autism themselves.

The team looked at two things: how the babies acted and how the parents acted. They wanted to know if either side looked different between 6 and 12 months.

Babies who were later diagnosed with autism already showed fewer gestures and poorer back-and-forth play by 6–12 months. Parents, however, acted the same no matter which babies later got the diagnosis.

In short: the baby side of the dance looked off, but the parent side looked normal.

The review backs up earlier single studies like Wan et al. (2012) and Maddox et al. (2015). Those papers also saw lower liveliness and social engagement in high-risk babies, while parent behavior did not differ.

Merin et al. (2007) and Geurts et al. (2008) add eye-gaze and joint-attention gaps at the same 6–12 month window, giving the review more bricks for the same wall.

Davidovitch et al. (2018) extends the story by showing that even low-risk babies later diagnosed with ASD slip in language and motor skills by 9 months. Together these works draw a clear line: the first year is packed with early signs, and parent style is not the trigger.

If you screen or coach families with babies who have an older sibling with ASD, watch the infant, not the parent. Look for fewer pointing, showing, or warm back-and-forth games before the first birthday. These tiny gaps are ready-made goals for parent-mediated therapy—parents can learn to respond more to the gestures that are already there, even if they didn’t cause the delay.