Analysis of Verbal Disability in Duchenne Muscular Dystrophy

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Abstract
There is recent evidence to suggest that Wechsler Intelligence Scale for Children (WISC) Verbal Scale IQ is more commonly and significantly impaired than Performance Scale IQ in males with Duchenne muscular dystrophy. This has been interpreted as the effect of some physical parameter of the disease upon central nervous system functioning. The purpose of the present study was to examine whether this verbal deficit was due to a verbal expression disability only or to a more comprehensive language problem involving a verbal expression as well as a verbal mediation deficit. Seven males with a 12-point discrepancy between WISC verbal and Performance Scale IQs were administered the Hiskey-Nebraska Test of Learning Aptitude (HNTLA), a nonverbal test of cognitive ability designed for use with the deaf and the hearing impaired, but with norms available for hearing children. In each of the seven cases, the HNTLA deviation quotient(comparable to IQ) corresponded more closely to the higher WISC Performance IQ, suggesting a verbal expression deficit but with most aspects of verbal mediation skills intact. Analysis of subtest scores on the WISC verbal and Performance Scales and the HNTLA found a consistent pattern, with higher scores on those subtests requiring abstract reasoning and categorization ability and lower scores on those subtests requiring memory for patterns, numbers, and verbal labels. This further suggests a deficit in memory function, which is a component of verbal mediation.