Williams syndrome

The fellowship mark goes to the candidate who thinks in three layers at once. The first is the child's heart: the elastin arteriopathy is the leading cause of morbidity and mortality, and the coronary arteries are its most dangerous and most easily missed expression. The second is the gene dose: a microdeletion of about 1.5 to 1.8 megabases at 7q11.23 removes one copy of elastin and a cluster of neurodevelopmental genes, and the phenotype is the sum of those haploinsufficiencies. The third is the family and the function: an affected parent changes the recurrence risk from background to one in two, and a sociable, verbal child still needs real support because the speech conceals a genuine intellectual and daily-living disability. [2] [5]

Overview & Definition

Williams syndrome, also called Williams-Beuren syndrome, is a multisystem contiguous-gene microdeletion syndrome caused by the hemizygous deletion of approximately 1.5 to 1.8 megabases at chromosome 7q11.23, a region containing 26 to 28 genes. The deletion produces a recognisable constellation of distinctive facies, a cardiovascular arteriopathy dominated by supravalvular aortic stenosis, infantile hypercalcaemia, intellectual disability with a characteristic cognitive profile, and a hypersocial personality. It affects roughly one in 7,500 to one in 10,000 live births, with no racial or sex predilection. [1] [2]

Clinically, Williams syndrome is the paradigm of how the loss of a handful of dosage-sensitive genes produces a coherent multisystem phenotype. Haploinsufficiency of the elastin gene (ELN) accounts for the cardiovascular and connective-tissue features — the narrowed, thickened arteries, the herniae, joint laxity, soft skin. Loss of the neighbouring GTF2I, GTF2IRD1, and LIMK1 genes accounts for the intellectual disability, craniofacial gestalt, hypersocial personality, and the visuospatial construction deficit. The syndrome is therefore best taught and best examined as the sum of its haploinsufficiencies, not as a single disease. [2] [5]

Historically, the syndrome was assembled from two separate descriptions: in 1961, the New Zealand cardiologist J. C. P. Williams reported supravalvular aortic stenosis with a distinctive facies and intellectual disability, and in the same year the German physicians A. J. Beuren and colleagues described a similar constellation. The historical name idiopathic infantile hypercalcaemia with supravalvular aortic stenosis captures the two features that first brought the syndrome to clinical attention, and the obsolete lay term elfin facies is now avoided because it is considered pejorative; use distinctive or characteristic facies. [8]