Williams syndrome: 15 years of psychological research.

Williams syndrome is a rare genetic disorder caused by a microdeletion of about 20 genes on chromosome 7q11.23. The importance of this syndrome for theories and models of cognition became apparent about 15 years ago, when Bellugi, Sabo, and Vaid (1988) argued that Williams syndrome was a paradigm case of the independence of language from cognition. In particular, it was argued that individuals with Williams syndrome have "intact" language despite severe mental retardation. More recent findings indicate a more complex relation between language and characteristics associated with this syndrome. The articles in this special issue form 3 overlapping clusters: articles concerned with language development relative to cognitive development, articles concerned with other aspects of cognition, and articles concerned with interpersonal relations and personality. Together, these articles provide strong evidence of the importance of the study of neurodevelopmental genetic disorders for enhancing understanding of the complex manner in which initial genetic differences impact both behavior and processing strategies from infancy through adulthood. Our hope is that this issue will motivate further studies, informed by the genetic-developmental approach, on both Williams syndrome and other neurodevelopmental genetic disorders.