In a retrospective study, data were assessed from cases regarding PWS/AS that underwent molecular diagnosis at the National Chen-Kung University Hospital, Tainan, Taiwan, between January 2001 and December 2014.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are two distinct syndromes of developmental impairment that result from loss of the expression of imprinted genes on the q11-q13 region of chromosome 15 (15q11-q13). Approximately 70%--75% of individuals affected with PWS and AS have an interstitial deletion of 15q11-q13. Regarding the remaining individuals with PWS, maternal uniparental disomy is the cause in 20% of cases, imprinting errors in 3% of cases, and chromosomal translocation in approximately 1% of cases. Regarding the remaining cases of AS, paternal uniparental disomy accounts for 2% of cases and mutations in the UBE3A gene for 20% of cases.The PWS/AS critical region was examined by fluorescence in situ hybridization (FISH), methylation-specific PCR (M-PCR), and methylation-specific multiplex-ligation dependent probe amplification(MS-MLPA). In a retrospective study at the National Chen-Kung University Hospital,Tainan, Taiwan, data were reviewed from cases that were referred for molecular diagnosis between January 1, 2001, and December 31, 2014.

Inclusion Criteria:

• Individual with clinical features related to Prader-Willi syndrome or Angelman syndrome;
• Fetus with suspicious deletion or duplication of chromosome 15q11.2-q13 visible by the microscope;
• Fetus whose mother or father has chromosomal abnormality involving 15q11.2-q13
• Fetus with mosaic trisomy 15

Exclusion Criteria:

During January 1, 2001, and December 31, 2014, cases were referred for molecular diagnosis such as individual with clinical features related to Prader-Willi syndrome or Angelman syndrome ; fetus with deletion or duplication of chromosome 15q11.2-q13 visible by the microscope; fetus whose mother or father has chromosomal abnormality involving 15q11.2-q13 and fetus with mosaic trisomy 15