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Table 1 Molecular defects and recurrence risks in PWS.

From: Practice guidelines for the molecular analysis of Prader-Willi and Angelman syndromes

Genetic defect Proportion of cases Recurrence risk
De novo deletion of 15q11-q13 on the paternal chromosome 75-80% <1%
Maternal uniparental disomy (UPD) of chromosome 15 20-25% <1%
Imprinting defects (with an imprinting centre deletion excluded) ≈1% <1%
Imprinting centre deletion ≈ 10-15% of patients with an imprinting defect Up to 50% (if present in father)