Is fragile X syndrome a pervasive developmental disability? Cognitive ability and adaptive behavior in males with the full mutation

Publisher Website
Google Scholar
Abstract
In addition to mental retardation (MR), fragile X [fra(X)] syndrome has been associated with various psychopathologies, although it appears that the link is secondary to MR. It has been proposed that individuals with the full mutation be classified as a subcategory of pervasive developmental disorders (PDD). If fra(X) males are to be categorized as PDD, how do they compare with other types of developmental disabilities? We examined 27 fra(X) males aged 3–14 years, from 4 sites in North America. Measures of cognitive abilities were obtained from the Stanford‐Binet Fourth Edition (SBFE), while levels of adaptive behavior were evaluated using the Vineland Adaptive Behavior Scales (VABS). Control subjects were sex‐, age‐, and IQ matched children and adolescents ascertained from the Developmental Evaluation Clinic (DEC) at Kings County Hospital. At the DEC, control subjects were diagnosed as either MR (n=43) or autistic disorder (AD; n=22). To compare subjects' adaptive behavior (SQ) with their cognitive abilities (IQ), a ratio of {(SQ/IQ)x100} was computed. Results graphed as cumulative distribution functions (cdf) revealed that the cdf for AD males, who by definition are socially impaired, was positioned to the left of the cdf for MR controls, as expected. Mean ratio for AD males (70) was lower than for MR males (84). On the other hand, the cdf for fra(X) males was positioned far to the right of either AD or MR controls (mean ratio = 125). Statistical tests showed that SQ of fra(X) males was significantly higher than controls. Moreover, in 23/26 (88%) of the fra(X) males tested, SQ was greater than IQ, indicating that adaptive behavior was not as impaired as cognitive abilities. Our results have consequences for the clinical evaluation of fra(X). In particular, fra(X) individuals may appear to function at higher cognitive levels than may be the case. We suggest that, while fra(X) may produce mild to profound developmental delay, it should not be included as a separate subtype of developmental disorder.

This publication has 25 references indexed in Scilit: