FRAGILE-X-SYNDROME A PERVASIVE DEVELOPMENTAL DISABILITY - COGNITIVE-ABILITY AND ADAPTIVE-BEHAVIOR IN MATES WITH THE FULL MUTATION

In addition to mental retardation (MR), fragile X [fra(X)] syndrome ha s been associated with various psychopathologies, although it appears that the link is secondary to MR. It has been proposed that individual s with the full mutation be classified as a subcategory of pervasive d evelopmental disorders (PDD). If fra(X) males are to be categorized as PDD, how do they compare with other types of developmental disabiliti es? We examined 27 fra(X) males aged 3-14 years, from 4 sites in North America. Measures of cognitive abilities were obtained from the Stanf ord-Binet Fourth Edition (SBFE), while levels of adaptive behavior wer e evaluated using the Vineland Adaptive Behavior Scales (VABS). Contro l subjects were sex-, age, and IQ matched children and adolescents asc ertained from the Developmental Evaluation Clinic (DEC) at Kings Count y Hospital. At the DEC, control subjects were diagnosed as either MR ( n=43) or autistic disorder (AD; n=22). To compare subjects' adaptive b ehavior (SQ) with their cognitive abilities (IQ), a ratio of {(SQ/IQ)x 100} was computed. Results graphed as cumulative distribution function s (cdf) revealed that the cdf for AD males, who by definition are soci ally 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 t o the right of either AD or MR controls (mean ratio = 125). Statistica l tests showed that SQ of fra(X) males was significantly higher than c ontrols. Moreover, in 23/26 (88%) of the fra(X) males tested, SQ was g reater 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, i t should not be included as a separate subtype of developmental disord er. (C) 1994 Wiley-Liss, Inc., Inc.