Introduction

Williams-Beuren syndrome (WBS; also called Williams syndrome) is a multisystem developmental disorder that is almost always associated with an approx 1.5-Mb deletion of chromosome 7q11.23 (OMIM no. 194050). The deletion was identified in 1993 based on the observation of phenotypic overlap with supravalvular aortic stenosis (SVAS), a distinct autosomal dominant disorder affecting the cardiovascular system (1). It has since been shown that SVAS arises because of the disruption of one copy of the elastin gene, through either deletion, translocation or point mutation (2-4), but the genes contributing to the remaining aspects of WBS have not yet been definitively determined.

The 7q11.23 chromosomal region that is commonly deleted in WBS contains more than 25 genes and, as might be expected, is flanked by chromosome-specific low-copy repeats (LCRs) (5,6). The nature of these repeats are such that in addition to deletions (and presumably the reciprocal duplications), inversions of the region are also mediated, one of which exists as a polymorphism that seems to predispose to the deletion (7,8). The increasing number of genomic rearrangements being discovered to be associated with this region are, therefore, not only expanding the repertoire of molecular diagnostic tests for WBS and its associated pheno-types, but also impacting on genetic counseling for this disorder. To facilitate future molecular genetic studies involving the WBS locus, we are actively cataloging chromosome rearrangements involving the WBS-LCRs and associated phenotypes. The clinical and molecular data can be found at http://www.chr7.org/.

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