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Table 2 Molecular defects and recurrence risks in AS.

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 maternal chromosome 70-75% <1%
Paternal uniparental disomy (UPD) of chromosome 15 3-7% <1%
Imprinting defect (with an imprinting centre deletion excluded) 2-3% <1%
Deletions of the imprinting centre ≈ 10-15% of patients with an imprinting defect Up to 50% (if present in mother)
UBE3A mutation ≈10% 50% if present in mother
No identifiable molecular abnormality ≈10% Unknown (up to 50%)