Background and Purpose: Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are caused by deficiencies of gene expression from paternal or maternal chromosome 15q11-q13, respectively. The study was conducted to estimate the prevalence of PWS and AS in children with moderate to profound mental retardation in Taiwan. Methods: The screening began with methylation studies in all enrolled cases. If methylation results were positive, Fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) was used to determine whether deletion, uniparental disomy, or imprinting mutation was present. Results: Of 1053 children with moderate to profound mental retardation, we identified three cases of AS (0.28%) and one case of PWS (0.09%). Conclusions: The prevalence of PWS is lower than AS in school children with moderate to profound mental retardation. The greater number of AS identified than that of PWS is most likely a reflection of more severe mental retardation for AS than for PWS. 背景：Prader-Willi氏及Angelman氏症候群雖然在臨床表現有不同的症狀，卻是同樣在染色體15q11-q13分別有來自父親及母親基因表現的缺失，此乃導因於基因的銘記效應。方法：我們總共收集1053個中度到深重度的智障學童，首先用甲基化方法篩檢所有學童，若甲基化實驗呈現陽性，再進一步用FISH及PCR方法區分是否有染色體缺失，單親二體症或基因帶有錯誤的印記所導致的異常。結果：總共發現了三個Angelman氏症候群的學童(0.28%)及一個Prader-Willi氏症候群的學童(0.09%)。在這次的篩檢中，Angelman氏症候群的學童之盛行率高於Prader-Willi氏症候群最可能的原因可能是來自於採樣的偏差，因為An-gelman氏症候群造成的智障往往比Prader-Willi氏症候群來的嚴重。結論：在南台灣地區的重度到深重度智障的學童中，Prader-Willi氏症候群之盛行率比Angel-man氏症候群低，主要的原因乃Angelman氏症候群所造成的智障以重度及深重度為主所導致。
