Autism spectrum phenotype in males and females with fragile X full mutation and premutation.

Clifford et al. (2007) looked at how often autism shows up in fragile X syndrome.

They gave the ADOS-G and ADI-R to males and females who had either the full mutation or the smaller premutation.

The team then counted how many people in each group met autism criteria.

Two out of every three males with the full mutation met ASD cut-offs.

Only about one in four females with the full mutation did.

In the premutation group, the numbers were much lower: 14 % of males and 5 % of females.

Schaaf et al. (2015) later asked the same question with DSM-5 rules. Their larger survey found the new rules drop the FXS-ASD rate by roughly one-third.

Scott et al. (2018) used the 2007 rates as a baseline and showed that boys with both FXS and autism have weaker daily-living and academic skills.

Joga-Elvira et al. (2021) zoomed in on girls and found executive function—not autism status—best predicts their real-life skills, adding nuance to the 2007 female numbers.

If you assess a child with FXS, expect autism traits most often in boys with the full mutation. Still, check girls and premutation carriers; the odds are lower but real. Use ADOS-G/ADI-R for research accuracy, yet know DSM-5 criteria will shrink your caseload. Pair autism results with executive-function and adaptive-skill tests so your intervention plan targets the true drivers of independence.