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The incidence of typical forms is 1/20 000 births, however, partial forms also exist but their incidence is unknown.

Williams syndrome associates a cardiac malformation (most frequently supra valvular aortic stenosis, SVAS) in 75% of cases, psychomotor *delay, a characteristic facial dysmorphism and a specific cognitive and behavioural profile. Children suffering from Williams syndrome present with a very characteristic face: flattened nasal bridge with a bulbous tip, large mouth with a wide everted lower lip, chubby cheeks, periorbital oedema, epicanthus and often stellar iris. With age, the face becomes narrower with coarser features. The cognitive profile is dominated by visuospatial deficits, which contrast with relatively well-preserved language skills. Affected children display hypersocial behaviour and interact well with other people. They have a distinctive sensitivity to noise and have good musical abilities. The prevalence of tooth decay is increased, and sometimes associated with enamel hypoplasia. Ophthalmologically, 40% of the affected children present with strabismus and/or refraction disorders. Vascular malformations such as SVAS and pulmonary or renal artery stenosis, which can lead to renovascular arterial hypertension, can be observed from birth. Hypercalcaemia can progress to nephrocalcinosis.

Williams syndrome is caused by a chromosomal microdeletion in the q11.23 region of one copy of chromosome 7. This microdeletion, which generally occurs sporadically, results in the loss of many genes, including the elastin gene.

It can not be detected conventional karyotyping and is revealed by FISH (Fluorescent In Situ Hybridization) analysis, which leads to diagnosis in 95% of the cases.

Vascular malformations require regular follow-up as well as dedicated management. For this reason, children affected by Williams syndrome should be managed by a paediatric cardiology team with knowledge of this pathology. The management of arterial hypertension requires a combination of pharmaceutical treatment with a healthy diet and lifestyle. The decision to opt for surgical repair of renal artery stenosis must take into account the global involvement of the vascular walls in this pathology. Hypercalcaemia is treated by a calcium-restricted diet. Arterial tension and renal function require life-long surveillance. Educational management of children affected by Williams syndrome should be proposed in a multidisplinary setting involving paediatricians, orthodontists, psychomotricists, speech therapists and psychologists.

Adult patients are rarely self-sufficient.