Williams Syndrome Inheritance: How the Condition Is Passed Down

Williams syndrome (WS) is caused by a heterozygous microdeletion of ~1.5–1.8 Mb on chromosome 7q11.23, encompassing the ELN (elastin) gene and ~25–27 other genes.

Inheritance Pattern

• Autosomal Dominant: One deleted copy of 7q11.23 is sufficient to cause the syndrome.
• De Novo Majority: ~95% of cases are de novo (neither parent carries the deletion). Recurrence risk for siblings <1% (gonadal mosaicism possible but rare).
• Inherited Cases: ~5% inherit from an affected parent. If a parent has WS, each child has a 50% chance of inheriting the deletion.

Genetic Counseling Implications

• Parents of a child with WS should have FISH/microarray testing to rule out mosaicism or balanced translocation (extremely rare).
• If parent is affected → 50% recurrence risk; prenatal diagnosis (CVS/amnio + microarray) available.
• If child is de novo → siblings at population risk (~1:10,000); offspring of affected individual = 50%.

Phenotypic Variability

Deletion size is usually similar (common flanking repeats mediate recombination), but expression varies — cardiovascular severity (SVAS), cognitive profile, personality, endocrine issues. Modifiers and environment play roles.

Resources

• Williams Syndrome Association — family support, clinics, research.
• GeneReviews (NIH) — authoritative clinical summary.
• Mayo Clinic — patient-friendly overview.