A longitudinal assessment of diverging verbal and non-verbal abilities in the Williams syndrome phenotype.

Jarrold et al. (1998) presented evidence to suggest that verbal and non-verbal abilities develop at different rates in individuals with the Williams syndrome phenotype. However, this evidence was derived from cross-sectional rather than longitudinal data. The current report presents data from a series of follow up assessments which examine the development of vocabulary and pattern construction abilities in 15 of the original sample of 16 individuals, over a 40 month period. The results confirm the original predictions, as mental age equivalent scores for vocabulary increase more rapidly than scores for the pattern construction test; a finding, which appears unlikely to be due to practice effects.