Cognitive profile difference between normally intelligent children with Asperger's disorder and those with pervasive developmental disorder not otherwise specified.

AIM: Asperger's disorder (Asperger syndrome, AS) and pervasive developmental disorder not otherwise specified (PDD-NOS) are different subtypes of mild pervasive developmental disorders (PDD).

METHODS: Using the Japanese version of the Wechsler Intelligence Scale for Children-Third Edition (WISC-III), 28 AS children (mean age, 9.3 years, 24 male) were compared with 78 PDD-NOS children (mean age, 7.6 years, 64 male) with normal intelligence (IQ > or = 85), using analysis of covariance (ancova) with the chronological age of a child as a covariate.

RESULTS: Verbal IQ tended to be higher in the AS children than in the PDD-NOS children (mean raw scores, AS vs PDD-NOS: 103.9 vs 99.6; P < 0.10), although full-scale and performance IQ did not differ significantly. Compared with the PDD-NOS children, the AS children scored significantly higher on Freedom from Distractibility index (110.1 vs 104.5; P < 0.05) consisting of Arithmetic (11.0 vs 9.9, P = 0.04) and Digit Span (12.4 vs 11.6, P = 0.051), but tended to score lower on Coding (8.5 vs 9.8, P = 0.08).

CONCLUSION: The typical cognitive profile of PDD (i.e. low score on Comprehension and high score on Block Design) was shared by both groups, which may support the validity of the current diagnostic classification of PDD. Relatively better verbal ability in AS children seems to reflect their normal language acquisition in infancy, and strong numeric interest may produce the AS children's mathematical excellence over PDD-NOS children. A low score on Coding in AS children might reflect their extreme slowness, circumstantiality and/or drive for perfection.