Table 2.

Risks to Sibs of a Proband with AS by Genetic Mechanism

Molecular Class 1FamiliesGenetic MechanismRisk to Sibs
Ia65%-75%5- to 7-Mb deletion<1%
Ib<1%Unbalanced chromosome translocation or inherited small interstitial deletionPossibly as high as 50%
IIa3%-7%Paternal UPD<1%
IIb<1%Paternal UPD with predisposing parental translocationApproaching 100% if father has a 15;15 Robertsonian translocation
IIIa0.5%ID with deletion in the ICAs high as 50% if mother also has IC deletion
IIIb2.5%ID without deletion in the IC<1%
IV11%UBE3A pathogenic variantAs high as 50% if mother also has a pathogenic variant
V10%-15%"Other" - no identifiable molecular abnormalityUndetermined risk

ID=imprinting defect

IC=imprinting center


Based on terminology by Jiang et al [1999]

From: Angelman Syndrome

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