VERBAL AND NONVERBAL ABILITIES IN THE WILLIAMS-SYNDROME PHENOTYPE - EVIDENCE FOR DIVERGING DEVELOPMENTAL TRAJECTORIES

One commonly cited feature of Williams syndrome is a characteristic di ssociation between relatively spared language skills and severely impa ired nonverbal abilities. However, the actual evidence for a dissociat ion between verbal and nonverbal abilities in Williams syndrome is equ ivocal. In two separate studies we examined these abilities in 16 indi viduals showing the Williams syndrome phenotype. When considered as a whole, the group did have significantly superior verbal abilities, but this difference was caused by a large discrepancy in abilities in onl y a small number of individuals. In both studies there was a clear, li near relation between individuals' verbal ability, and the magnitude o f their verbal-nonverbal discrepancy. We suggest that these results ar e best explained in terms of verbal ability developing at a faster rat e than nonverbal ability in this disorder. We discuss how this model o f differential rates of development has the potential to reconcile the apparently inconsistent findings in this area.