Prader-Willi and Angelman syndromes both result from abnormalities of chromosome 15q11-q13 but have distinct phenotypes. Prader-Willi syndrome arises when the deleted or inactivated chromosome 15q11-q13 region is of which parental origin?

• A Maternal deletion or paternal uniparental disomy
• B Paternal deletion only; maternal origin not involved
• C Paternal deletion or maternal uniparental disomy ✓
• D Maternal deletion only; paternal origin not involved

Explanation

Prader-Willi syndrome results from loss of the paternally expressed genes at 15q11-q13: this occurs either by deletion of the paternal allele (~70% of cases) or maternal uniparental disomy (both chromosomes 15 inherited from the mother, so no paternal contribution). Angelman syndrome is the opposite: loss of maternally expressed UBE3A gene — maternal deletion or paternal UPD. This reflects genomic imprinting, where expression depends on the parental origin of the chromosome.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.