Objective: To measure the genetic and environmental factors influencing the cognitive outcomes in children with fragile X, a common genetic disorder causing cognitive impairments.
Method: In-home evaluations were conducted on 120 children (80 boys and 40 girls) with the fragile X full mutation and their unaffected siblings.
Results: Multiple regression analyses show that the cognitive outcomes for girls with fragile X are most strongly predicted by the mean IQ of their parents, with a small proportion of the variance accounted for by the quality of their home environment. FMR1 protein (FMRP) was associated with girls' levels of distractibility. Mean parental IQ was associated only with boys' Performance IQs, while FMRP was associated with boys' Full Scale IQs. The quality of boys' home environments accounted for more of the variance in their cognitive outcomes than it did for affected girls.
Conclusions: Both biological/genetic factors and environmental factors are significant predictors of IQ in children with fragile X syndrome; however, the influence of specific factors differs between girls and boys. These findings lay the foundation for further investigation into biological and environmental interventions.