Establishment of genetic diagnosis and genetic counseling of Angelman syndrome.

Angelman综合征（AS）是一种与基因组印记相关的神经发育障碍。AS是由位于15q11-q13的印迹UBE3A基因功能缺陷引起的。由于多种遗传缺陷可导致UBE3A缺乏症，因此进行适当的遗传诊断以评估复发风险并提供遗传咨询非常重要。我们开发了由DNA甲基化分析、微卫星多态性、印迹中心分析、UBE3A突变筛查组成的系统遗传诊断系统，实现了对所有遗传类的诊断。我们研究了85例无15q11-q13共同缺失的Angelman综合征患者，检测到7例15号染色体父本单亲二体，7例印迹缺陷，23例UBE3A突变。因此，67%的缺失阴性Angelman综合征被我们开发的系统遗传诊断系统诊断出来。所有患者均为散发型。印迹中心分析没有在任何有印迹缺陷的患者中发现印迹中心的微缺失，因此这些患者被认为有印迹突变。UBE3A突变位于该基因的不同部位。5个突变位于第16外显子3089 ~ 3095处，为日本人突变热点。我们检查了8位携带UBE3A突变患者的母亲，8位母亲中有2位携带相同的突变，因此她们是携带者，而6位突变是从头产生的。本研究可为日本人群Angelman综合征的遗传咨询提供重要信息。

Angelman syndrome (AS) is a neurodevelopmental disorder associated with genomic imprinting. AS is caused by functional deficit of the imprinted UBE3A gene located in 15q11-q13. Because several genetic defects could cause UBE3A deficiency, it is important to make proper genetic diagnosis to assess recurrence risk and offer genetic counseling. We have developed the systemic genetic diagnosis system which is composed by DNA metylation analyis, microsatellite polymorphism, imprinting center analysis, and UBE3A mutation screening so that all genetic classes can be diagnosed.We studied 85 Angelman syndrome patients without a common deletion of 15q11-q13, and detected 7 patients with paternal uniparental disomy of chromosome 15, 7 patients with an imprinting defect, and 23 patients with a mutation in UBE3A. Therefore, 67% of deletion-negative Angelman syndrome was diagnosed by the systemic genetic diagnosis system we have developed. All patients with uniparental disomy were sporadic. Imprinting center analysis did not identify a microdeletion of the imprinting center in any of patients with an imprinting defect, therefore these patients was thought to have an epimutation. UBE3A mutations were located in various parts of the gene. Five mutations were located at 3089- 3095 by in exon 16 indicated the hot spot of mutations in Japanese. We examined 8 mothers of patients with a UBE3A mutation, 2 out of 8 mothers carried the same mutation and therefore they were carriers, while 6 mutations arose de novo.Our study should provide important information for genetic counseling of Angelman syndrome in Japanese population.