Technologies for mapping interspersed AGG sequences in the FMR1 gene

描述（由申请人提供）：该项目的目标是开发一套全面的检测方法，以改善与脆性X综合征（FXS）相关疾病的筛查和预测。FXS影响约1/4000男性和1/6000女性，是由FMR1基因52非翻译区（UTR）的胞嘧啶-鸟嘌呤-鸟嘌呤（CGG）三重重复扩增引起的。正常的FMR1基因在52 UTR中包含多达40个CGG三胞胎，而渗透的全突变基因的特征是超过200个重复，基因的高甲基化和FMR1蛋白生产的完全丧失。CGG重复序列的适度扩展（预突变）与成人运动、生殖和认知障碍有关。CGG扩张也与自闭症谱系障碍（ASD）有关。当排列重复序列处于“灰色地带”（~30-50个CGG重复序列）时，可以发生从突变前到完全突变状态的世代扩展，但在适当位置散布的腺嘌呤-鸟嘌呤-鸟嘌呤（AGG）序列可以赋予基因稳定性。从FMR1基因扩增的群体研究中，已经提出了CGG重复序列中散布的AGG序列与预测突变前或完全突变等位基因扩增的相关性。据推测，AGG重复导致脆性X相关疾病的风险降低。因此，改进对脆性X染色体的检测将对广泛的男女和所有年龄的个体具有重要的意义，这些个体有可能患上与这种疾病相关的各种疾病。在这些研究中，我们将扩展现有的CGG重复分析，以开发一套准确绘制FMR1基因52个非翻译区CGG重复序列中散布的AGG序列的检测方法。这些检测将确定这些AGG三胞胎的频率和位置，区分女性中的等位基因，并具有绘制马赛克中次要等位基因的敏感性，这些特征在目前可用的FXS检测中是不具备的。我们的目标是建立一个综合的诊断工作流程，该流程具有成本效益，无需专门设备即可常规用于FXS筛选。这些检测将有助于诊断，改善FXS和相关疾病的遗传咨询服务，从长远来看，可用于胎儿和新生儿筛查。此外，AGG分布与CGG过度扩张相关性的人群研究将通过这些检测得到促进。

DESCRIPTION (provided by applicant): The objective of this project is to develop a comprehensive set of assays to improve screening and prediction of conditions associated with fragile X syndrome (FXS). FXS, which affects approximately 1/4000 men and 1/6000 women, is caused by an expansion of a cytosine-guanine-guanine (CGG) triplet repeat in the 52 untranslated region (UTR) of the FMR1 gene. The normal FMR1 gene contains up to 40 CGG triplets in the 52 UTR, while the penetrant, full mutation gene is characterized by greater than 200 repeats, hypermethylation of the gene and complete loss of FMR1 protein production. A more modest expansion of the CGG repeats (premutation) has been linked to adult movement, reproductive and cognitive disorders. CGG expansion has also been implicated in autism spectrum disorder (ASD). Generational expansion from premutation to full mutation state can occur when permutation repeats are in the "gray zone" (~30-50 CGG repeats), but interspersed adenine-guanine-guanine (AGG) sequences in the proper locations can confer stability to the gene. The relevance of interspersed AGG sequences in the CGG repeats for predicting expansion to premutation or full mutation alleles has been proposed from population studies of FMR1 gene expansion. It is hypothesized that AGG repeats lead to lower risk of developing Fragile X associated diseases. Therefore, improved testing for fragile X will have important implications for a broad range of individuals of both sexes and all ages at risk of the various conditions associated with this disorder. In these studies we will expand our existing CGG repeat assay to develop a set of assays that will accurately map interspersed AGG sequences that occur within the CGG repeats in the 52 untranslated region of the FMR1 gene. The assays will determine the frequency and positions of these AGG triplets, distinguish between alleles in females, and have the sensitivity to map minor alleles in mosaics, features that are not available on currently available FXS tests. Our goal is a comprehensive diagnostic workflow that is cost-effective and can be routinely used for FXS screening without the need for specialized equipment. The assays will serve as an aid to diagnosis, improve the provision of genetic counseling for FXS and associated disorders, and in the long term, could be used for fetal and newborn screening. Furthermore, population studies of the relevance of AGG interspersion on CGG hyperexpansion will be facilitated with these assays. PUBLIC HEALTH RELEVANCE: Fragile X disease is one of the most common forms of inherited mental retardation, and its genetic cause has been linked to autism, adult reproductive, movement and cognitive disorders. New genetic analysis techniques developed in these studies will provide clinical risk assessment and genetic counseling tools for this devastating group of diseases.