小胖威利症候群是一種罕見的神經行為上的遺傳疾病，症狀包括輕度到中度智能障礙、嬰兒時期肌肉低張力、外陰部發育不良、發育遲緩、身材矮小、手掌及腳掌偏小、嬰兒期後因過於旺盛的食慾導致肥胖並伴有早發性糖尿病的發生。目前已知其發病原因在於第十五號染色體上的小核內核糖核蛋白(SNRPN)異常所導致。此基因受基因印記的遺傳機制所調控，因此百分之七十的PWS病患起因來自於父方的第十五號染色體缺失，百分之廿五是由於母源單親二體症導致，即兩條十五號染色體皆源自母方。本研究嘗試以甲基聚合酵素連鎖反應作為第一線分子診斷的工具，針對200位PWS可能患者的檢體進行篩檢，發現其中有30位為PWS患者，與臨床表徵吻合。結果顯示此方法能準確診斷PWS發病成因，若能以螢光原位雜交及小微星標竿多形性基因標記作為母源單親二體症的檢查，更能使PWS的判定更加精確。此技術可使得家長能夠快速的得到結果，也能提早對於低張力的狀況做復健，並控制病童飲食避免過胖，同時也使得病童免於因肌肉低張力所進行的穿刺性檢查，在遺傳諮詢上提供有效協助。 Prader-Willi syndrome (PWS) is associated with distinct phenotypes which include mental retardation and caused by loss of function of genes, located in chromosome 15q11-q13, an area subjected to genomic imprinting. Methylation- specific polymerase chain reaction (M-PCR) based on parents of origin specific DNA methylation at the promoter region of small nuclear ribonucleoprotein polypeptide N gene (SNRPN) can provide accurate and rapid diagnosis for nearly all PWS patients. We report on the development of a referral system for molecular diagnosis of PWS based on M-PCR. Pediatric geneticists, psychiatrists or neurologists were asked to evaluate phenotypes of patients with PWS and complete a questionnaire designed according to the consensus criteria to diagnose these conditions. Molecular analysis based on M-PCR was performed for patients with a score of at least two. A total of 200 patients with suspected PWS were referred for diagnostic testing. PWS was diagnosed in 30 of these patients. M-PCR is a cost-effective method for the diagnosis of PWS.
