Brief Report: Phenotypic Differences and their Relationship to Paternal Age and Gender in Autism Spectrum Disorder.

Vierck et al. (2015) looked at simplex families—those with only one child with autism.

They asked whether dad’s age and the child’s sex shape the kind of repetitive behaviors the child shows.

No new test or therapy was tried; the team just mined the data that was already there.

Older dads and male children together predicted stronger repetitive and restricted behaviors.

The pattern stayed even after the researchers controlled for mom’s age and child IQ.

In plain words, age plus gender equals a bump in hand-flapping, lining up toys, or strict routines.

Sutton et al. (2022) extends the same idea to rating scales. On CARS2 and GARS-3, boys again score higher on most repetitive items, while girls only stand out for higher fear and nervousness.

Harrop et al. (2018) adds another layer: girls with autism keep typical face-looking habits, unlike boys. Together these papers show sex shapes both social and repetitive sides of autism, not just one.

Germani et al. (2014) seems to disagree at first—it found no sex gap in core autism symptoms after one year. The key difference is time: Tamara watched the same kids for 12 months, while Esther took a single snapshot. The gap may shrink as children grow, so both studies can be true.

If you evaluate a boy born to an older father, expect more intense repetitive behaviors and plan your baseline accordingly. For girls, watch for subtler signs like anxiety rather than obvious rituals. Adjust interview questions, choose norms by sex, and explain to parents why their child’s profile may look different from textbook examples.