Origins of Variarion in Abnormal FMR1 Methylation in Fragile X Syndrome

脆性X综合征通常由FMR 1基因座的两个异常变化引起-一个是遗传的，另一个是遗传的。 另一种表观遗传学遗传变化包括启动子区域CGG重复序列的大量扩增 FMR1。表观遗传变化包括两个男性FMR 1的CpG岛的密集甲基化 和女性脆性X染色体。FMR 1处异常甲基化的存在和程度最好 脆性X综合征认知功能障碍的分子预测因子在某些个体中，扩展重复 等位基因逃避了密集甲基化。这些人得到部分保护， 脆性X综合征患者的认知功能减退，但他们有患晚发性脆性X综合征的风险。 X相关震颤共济失调综合征（FXTAS），这似乎是由于转录过度表达 FMR1。因此，在扩增的FMR 1等位基因处甲基化的存在和不存在两者都是可能的。 与疾病有关。在过去的资助期间，我们开发了强大的新方法来分析 单个双链DNA分子的两条链上的甲基化模式。我们确定 细胞-细胞嵌合体有时存在于脆性X染色体个体中，而以前报道这些个体不存在。 马赛克。我们还排除了链间和位点间镶嵌现象作为意外发生的可能解释。 在一些完全突变的男性中FMR 1 mRNA水平较高。在这里提出的项目中，我们力求 了解个体间FMR 1异常甲基化程度的广泛差异的起源 与扩展重复等位基因，并在这些个人的细胞。具体来说，我们将建立 trans-chromosomal fragile X/human ES细胞系来研究异常甲基化的起源。我们 将询问是否在甲基四氢叶酸还原酶（MTHFR）基因座的基因型，以及 叶酸和生化相关化合物在组织培养基中的我们的反染色体脆性 X/人ES细胞，导致密集甲基化的概率和/或 FMR 1基因重复序列扩增我们还将分析现有的和额外的临床数据从脆性X 家庭询问是否母亲，父亲，和/或患者基因型在MTHFR基因座， 与FMR 1的重复扩增和/或甲基化相关。了解导致 FMR 1的表观遗传变异将进一步加深我们对脆性X和FXTAS患者风险的理解。

Fragile X syndrome typically results from two abnormal changes at the FMR1 locus -- one genetic and the other epigenetic. The genetic change consists of a large expansion of CGG repeats in the promoter region of FMR1. The epigenetic change includes dense methylation of the CpG island of FMR1 in both males and females with fragile X. The presence and extent of abnormal methylation at FMR1 is the best molecular predictor of cognitive impairment in fragile X syndrome. In some individuals, expanded repeat alleles escape dense methylation. These individuals are partially protected from the most severe decrement in cognitive function that occurs in fragile X syndrome, but they are at risk for late-onset Fragile X associated Tremor Ataxia Syndrome (FXTAS), which appears to result from transcriptional overexpression of FMR1. Thus, both the presence and absence of methylation at the expanded FMR1 allele are associated with disease. In the past grant period, we developed powerful new methods to analyze methylation patterns on both strands of individual double-stranded DMA molecules. We determined that cell-cell mosaicism is sometimes present in fragile X individuals who were previously reported not to be mosaic. We also excluded interstrand and intersite mosaicism as possible explanations for unexpectedly high levels of FMR1 mRNA in some full mutation males. In the project proposed here, we seek to understand origins of the wide variation in the extent of abnormal methylation of FMR1 among individuals with expanded-repeat alleles, and among the cells of those individuals. Specifically, we will establish trans-chromososomal fragile X/human ES cell lines to investigate the origin of abnormal methylation. We will ask whether or not genotype at the methyltetrahydrafolate reductase (MTHFR) locus, and the levels of folate and biochemically related compounds in tissue culture media of our trans-chromososomal fragile X/human ES cells, contribute to variation in the probability of dense methylation and/or the probability of genetic repeat expansion at FMR1. We will also analyze existing and additional clinical data from fragile X families to ask whether or not maternal, paternal, and/or patient genotypes at the MTHFR locus are correlated with repeat expansion and/or methylation at FMR1. Understanding the factors that contribute to epigenetic variation at FMR1 will further our understanding of patient risks for both fragile X and FXTAS.