LONGITUDINAL-STUDY OF COGNITIVE-ABILITIES AND ADAPTIVE-BEHAVIOR LEVELS IN FRAGILE-X MALES - A PROSPECTIVE MULTICENTER ANALYSIS

Retrospective longitudinal studies have noted declines in IQ scores in many but not all fra(X) (fragile X) males and females. We report on a prospective investigation of longitudinal changes in cognitive abilit y (IQ) and adaptive behavior (DQ) in 24 fra(X) males from four test si tes, Individuals who were tested ranged in age from 3-15 years, To det ermine cognitive ability, all males were administered the Stanford-Bin et test (4th Edition). To assess adaptive behavior, all males were eva luated using the Vineland Adaptive Behavior Scales. Mean intertest int erval was 2.3 years, Using identical DNA protocols, all subjects were identified as bearing the fra(X) mutation, Results showed declines in IQ scores in 18/24 (75%) males, Four males showed no change in scores. Declines in DQ scores were noted in 22/24 (92%) of those tested, DQ s cores were higher than IQ scores in 20/24 (83%) subjects. From a descr iptive cohort analysis, decreases in IQ scores appear to follow a well -defined, negatively decelerating function. Declines in DQ were steepe r and more nearly linear. Declining scores are not indicative of regre ssion of intellectual and/or social skills, but of a relative inabilit y to keep pace with their age-normed cohort. We conclude that the fra( X) mutation affects cognitive abilities in a uniform, nonlinear manner comparable to outcomes observed in earlier retrespective studies. Ada ptive behavior also declines, but in a more linear fashion, (C) 1996 W iley-Liss, Inc.