Implication of sex differences in the familial transmission of infantile autism.

The team looked at family histories of the children with infantile autism. They split the group by sex and counted who had low IQ, brain damage, or relatives with similar traits.

Records came from two hospitals. No tests or teaching were done; the study was pure description.

Girls with autism were three times more likely than boys to score below 50 on IQ tests. They also showed more brain damage and had more affected relatives.

The pattern hinted that autism in girls might travel through families differently.

Li et al. (2024) used brain scans four decades later and found the same girl-boy split: only girls with ASD showed extra network clustering. The 1981 clinical note and the 2024 imaging study line up—girls carry a different neural signature.

D'Agostino et al. (2025) tracked a whole state and saw girls getting diagnosed later than boys. Together with James et al. (1981), the message is clear: girls often look different, so they slip through the net.

Laposa et al. (2017) looked at toddlers entering early intervention and found no sex gap on IQ or symptoms. The clash is useful: at very young ages the differences may not yet show, or milder girls are the ones entering services.

When you screen, weigh family history more heavily for girls. If the girl also has low IQ or motor issues, push for genetics referral and watch for late-emerging symptoms. Do not wait for the classic boy-pattern red flags.