Cognitive, behavioral, and adaptive functioning in fragile X and non-fragile X retarded men.

Researchers compared grown men who have fragile X syndrome with men who have other causes of intellectual disability. All men lived in the same large residential center. The team gave IQ tests, behavior checklists, and daily-living skill scales.

They also noted which fragile X men had brothers or sisters with the same diagnosis. The goal was to see if fragile X itself predicts lower scores.

Men with fragile X scored almost the same on IQ and behavior tests as the other men with ID. Their daily-living skills were actually stronger once IQ was taken into account.

Within the fragile X group, men who had affected siblings scored higher on adaptive skills than men who were the only family member with the syndrome.

Jaffe et al. (2002) followed fragile X children and teens for several years. They saw IQ and daily-living scores drop over time. That seems to clash with the current study’s adult snapshot, but the difference is age: kids may lose skills while adults plateau.

Boudreau et al. (2015) tracked adolescents with fragile X and found verbal skills improved while non-verbal IQ slipped. Their data extend the 1988 adult picture by showing the mixed up-and-down path that leads to the adult plateau.

Olsson et al. (2001) added that boys with fragile X plus autism have slower growth than boys with fragile X alone. This refines the 1988 conclusion: fragile X alone does not predict outcome; the presence of autism does.

Do not assume fragile X alone explains your client’s skills. Use sibling history as a quick proxy: clients with affected siblings may need less daily-living support. Plan for possible skill loss during childhood, then stability in adulthood. Screen for autism separately; it drives more need than the fragile X label itself.