脆性X综合征的PCR筛查与诊断

采用多聚酶链反应（ＰＣＲ）技术结合变性序列胶银染方法对１６９例智力低下（简称智低）疑诊病例及６个脆性Ｘ综合征家系中３３名成员的ＦＭＲ１基因（ＣＧＧ）ｎ重复序列进行了分析，结果发现：（１）智低疑诊病例中３例男性未检出ＰＣＲ阳性产物；（２）脆性Ｘ综合征家系内，５例男性先证者亦未检出ＰＣＲ扩增带；（３）对上述ＰＣＲ结果为阴性的８例男性智低患者（此８例均经Ｓｏｕｔｈｅｒｎ印迹杂交证实为全突变患者），设立ＦＲＡＸＥ位点引物作内对照，结果仅获得ＦＲＡＸＥ位点的正常扩增产物，故而可排除ＦＲＡＸＡ位点ＰＣＲ产物为假阴性的可能。结果表明，ＰＣＲ分析ＦＭＲ１基因（ＣＧＧ）ｎ重复序列可有效检出前突变携带者，若男性智低患者的ＰＣＲ结果为阴性，在设立内对照基本排除假阴性的前提下，对本病也有提示作用。该方法快速、简便、稳定、可靠，适合于脆性Ｘ综合征的大量群体筛查。

Screening and Diagnosis of Fragile X Syndrome by PCR

Polymerase chain reaction (PCR) technique combined with direct detection by silver staining on denaturing DNA sequencing gel was applied to analyze the (CG G)n repeats within the FMR1 gene on 169 suspected patients with mental retardation and 33 kindreds of 6 fragile X families The results were shown as follows: (1) No PCR products were detected in 3 males in the suspected group (2) In the fragile X syndrome family studies, the 5 male probands failed to show any PCR products (3) Diplex PCR with the primers flanking the FRAXE locus was used to serve as an internal control for the above negative results in the 8 males Only normal products of the FRAXE locus were detected, and so the possibility of false negative results in the FRAXA locus could be ruled out These findings suggested that analysis of (CGG)n repeat within the FMR1 gene by PCR technique could efficiently detect premutation carriers and that negative PCR products in mentally retarded males might hint the diagnosis of fragile X syndrome after the false negative results had been excluded by the diplex PCR The PCR assay was suitable for the screening of fragile X syndrome in a large number of populations due to its rapidity, simplicity, stability and reliability