Introduction and Epidemiology
Williams syndrome is a rare, multisystem neurodevelopmental microdeletion disorder with an estimated incidence of 1 in 7,500 to 10,000 live births. It occurs equally in both sexes and across all ethnic groups.
Molecular Genetics and Pathogenesis
The condition is caused by a heterozygous contiguous gene deletion (1.5 to 1.8 megabases) on the long arm of chromosome 7 at locus 7q11.23. The vast majority of cases (>99%) occur sporadically due to a de novo meiotic recombination error during gametogenesis.
| Gene Involved | Pathophysiological Consequence |
|---|---|
| ELN (Elastin) | Haploinsufficiency causes connective tissue abnormalities, including supravalvular aortic stenosis (SVAS), peripheral pulmonary stenosis, joint laxity, premature skin wrinkling, and hoarse voice. |
| GTF2I and GTF2IRD1 | Implicated in the distinctive neurocognitive profile, visuospatial deficits, and craniofacial dysmorphism. |
| LIMK1 | Associated with impaired visual-motor integration and visuospatial constructive cognition. |
| NCF1 | Paradoxically decreases the risk of developing hypertension when included in atypical larger deletions. |
Clinical Manifestations
| System | Clinical Features |
|---|---|
| Craniofacial | ”Elfin facies”: broad forehead, bitemporal narrowing, periorbital fullness, epicanthal folds, stellate or lacy iris pattern, short nose with anteverted nares, malar hypoplasia, long smooth philtrum, wide mouth with full lips. |
| Cardiovascular | SVAS (present in up to 75%), peripheral pulmonary stenosis, hypertension (affecting ~50% of children and majority of adults), and thickened coronary arterial walls increasing ischemia risk. |
| Neurocognitive | Mild mental retardation (average IQ ~50), engaging extrovert (“cocktail party”) personality, good verbal and language skills contrasting with poor mathematical and visuospatial abilities, generalized anxiety, and hyperacusis. |
| Endocrine | Neonatal hypercalcemia, hypercalciuria, and hypothyroidism. |
| Gastrointestinal | Severe colic and feeding difficulties in infancy, gastroesophageal reflux disease, chronic constipation, diverticulitis, and rectal prolapse. |
| Renal | Structural abnormalities, renal artery stenosis, and nephrocalcinosis. |
| Musculoskeletal | Generalized joint laxity in early childhood progressing to contractures, kyphoscoliosis, radioulnar synostosis, and small widely spaced peg-shaped teeth. |
Diagnostic Evaluation
- Chromosomal Microarray (CMA): Primary diagnostic test confirming the 7q11.23 microdeletion and defining the exact size and boundary.
- Fluorescence In Situ Hybridization (FISH): Standard confirmatory test using an elastin (ELN) specific probe.
- Baseline Clinical Investigations: Urgent 4-limb blood pressure measurement, comprehensive echocardiography with Doppler flow studies, serum calcium (ionized and total), urine calcium-to-creatinine ratio, thyroid function tests, and renal ultrasonography with Doppler.
Management Principles
- Cardiovascular Care: Serial clinical exams and echocardiograms are mandatory. Surgical correction (e.g., patch aortoplasty) is indicated for hemodynamically significant SVAS.
- Hypertension Management: Aggressive medical management using calcium channel blockers or angiotensin receptor blockers.
- Anesthesia Warning: Extreme caution is required during general anesthesia due to a significantly increased risk of sudden cardiac death from decreased coronary perfusion in the setting of SVAS and biventricular hypertrophy.
- Endocrine and GI Care: Management of hypercalcemia often requires dietary restriction of calcium and vitamin D. Osmotic laxatives are used for chronic constipation.
- Long-Term Prognosis: Ultimate prognosis depends on the severity of cardiovascular involvement. The majority of adults require lifelong supportive care and supervised living arrangements due to intellectual disability and psychiatric comorbidities.