中文摘要：

脆性x综合征（FXS）是遗传性智力低下的常见原因，主要由FMR1基因突变导致（CGG）n序列异常扩增（n〉200）引起。但是，FMR1基因前突变（n=55-200）也可引起一系列的临床表现，其机制与FXS完全不同，为mRNA毒性机制。在1991年FMR1基因发现后的几年内，学者们普遍认为前突变携带者在临床上没有受累，只是女性携带者的CGG序列在遗传过程中可能发生扩增，导致子女患FXS。因此，临床医师很少注意前突变相关疾病，并且对于前突变和FXS之间的关系和区别普遍缺乏认识。现对FMR1基因前突变相关的临床表现、神经病理学和分子机制进行综述。

英文摘要：

Fragile X syndrome （FXS） is one of the common causes of inherited intellectual disability. It is mainly caused by the mutation of FMR1 gene which lead to （CGG） n abnormal amplification （n 〉 200）. However, the FMR1 gene premutation （ n = 55 - 200 ） can cause a series of clinical manifestations through an entirely distinct molecular mechanism from FXS,which involved increased FMR1 mRNA toxicity. A few years after the discovery of the FMR1 gene in 1991 ,it was generally believed that the carriers of premutation were clinically unaffected,but female car- riers of premutation had children with FXS. Thus, a few doctors pay attention to these disorders and generally lack of awareness the difference between the premutation and FXS. A review of the clinical manifestations, neuropathology and molecular mechanisms will show in the following paper.