Approximately 2-3% of Angelman syndrome (AS) cases are caused by paternal uniparental disomy of
chromosome 15. Characteristic features include severe mental retardation, absence of speech,
seizures and a happy disposition with unmotivated laughter. There are some reports that the UPD 15
AS phenotype is milder than that of AS caused by deletions in UBE3A,
while there have also been conflicting reports that some cases may infact be more severe (Poyatos
D et al. 2002). UPD and 15q11-q13 imprinting defects however produce phenotypes which are
clinically indistinguishable suggesting that this region contains the only imprinted regions on
chromosome 15 relevant to Angelman Syndrome (Lossie
AC et al. 2001).
Twenty-five to thirty percent of Prader-Willi cases result from maternal uniparental disomy of
chromosome 15 (Glenn
CC et al. 1997).