Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are caused by abnormalities involving the same region of chromosome 15q11-q13 but show DIFFERENT clinical phenotypes based on parental origin. A child with severe intellectual disability, seizures, happy demeanor, and ataxic gait has Angelman syndrome. The molecular mechanism is:
- A Deletion of paternal 15q11-q13 (loss of SNRPN, NDN)
- B Loss of maternal UBE3A expression (E3 ubiquitin ligase) in neurons ✓
- C Paternal uniparental disomy (patUPD) of chromosome 15
- D Methylation of the paternal imprinting center causing silencing of SNORD116
Explanation
Angelman syndrome results from loss of the maternal UBE3A allele (E3 ubiquitin-protein ligase). The paternal UBE3A is normally silenced in neurons by an antisense RNA mechanism (neuronal imprinting) — only the maternal UBE3A is expressed in neurons. Causes include: maternal deletion of 15q11-q13 (~70%), paternal uniparental disomy (~2-5%), UBE3A mutation (~10%), or imprinting defect. Prader-Willi syndrome results from loss of the PATERNAL contribution (deletion, maternal UPD, or paternal imprinting center defect), affecting SNRPN, MAGEL2, NDN expression. The happy demeanor with absent speech is key for AS.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.