Abstract：
Fragile X syndrome (FXS) is caused by an abnormal expansion of the number of trinucleotide CGG repeats located in the 5\' UTR in the first exon of the FMR1 gene. Size and methylation mosaicisms are commonly observed in FXS patients. Both types of mosaicisms might be associated with less severe phenotypes depending on the number of cells expressing FMRP. Although this dynamic mutation is the main underlying cause of FXS, other mechanisms, including point mutations or deletions, can lead to FXS. Several reports have demonstrated that de novo deletions including the entire or a portion of the FMR1 gene end up with the absence of FMRP and, thus, can lead to the typical clinical features of FXS. However, very little is known about the clinical manifestations associated with FMR1 gene deletions in mosaicism. Here, we report an FXS case caused by an entire hemizygous deletion of the FMR1 gene caused by maternal mosaicism. This manuscript reports this case and a literature review of the clinical manifestations presented by carriers of FMR1 gene deletions in mosaicism.
摘要：
脆性X综合征（FXS）是由位于FMR1基因第一个外显子5'UTR中的三核苷酸CGG重复序列数量异常增加引起的。在FXS患者中通常观察到大小和甲基化镶嵌。根据表达FMRP的细胞数量，两种类型的镶嵌可能与较不严重的表型相关。尽管这种动态突变是FXS的主要根本原因，其他机制,包括点突变或缺失，可以导致FXS。一些报道已经证明，包括整个或部分FMR1基因的从头缺失最终导致FMRP缺失，因此，可以导致FXS的典型临床特征。然而,关于镶嵌性FMR1基因缺失相关的临床表现知之甚少。这里,我们报道一例FXS病例,由母体镶嵌导致FMR1基因全合子缺失引起.本手稿报道了该病例，并对FMR1基因缺失携带者在镶嵌性中的临床表现进行了文献综述。
