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fra(X)智力低下或Martin-Bell综合征的诊断主要是依据Xq27脆性部位的细胞遗传学所见。但位于Xq27上的普通脆性部位可以导致假阳性结果;非外显和低表达可以导致假阴性结果。Veenema等于1981～1986年对428例受检者进行了细胞遗传学研究,其中291例为非特异性智力低下先证者(211个男性、80个女性)、101例为fra(X)阳性病人的一级亲属。对照组由36例无智力低下但有器官发育不全的病人所组成。每例受验者至少检查50个外周血淋巴细胞,在无叶酸培养基内培养、常规染色、镜检。检测结果与以前搜集的研究资料和对遗传风险及fra(X)外显率的预测资料进行比较。作者对每例受检者检测50个细胞时,如少于2个细胞表达脆性部位,被认为是阴性结果。细胞群中各种fra(X)表达(P)水平
fra (X) The diagnosis of mental retardation or Martin-Bell syndrome is mainly based on cytogenetics of the fragile site of Xq27. However, common fragile sites on Xq27 can lead to false-positive results; non-explicit and low-expression can lead to false-negative results. Veenema et al. Performed cytogenetic studies on 428 subjects between 1981 and 1986, of whom 291 were non-specific probands (211 males and 80 females) and 101 were fra (X) -positive patients First-degree relatives. The control group consisted of 36 patients without mental retardation but with organ dysplasia. Each subject examined at least 50 peripheral blood lymphocytes, cultured in folic acid-free medium, routine staining, microscopic examination. The test results are compared with previously collected research data and with estimates of genetic risk and fra (X) penetrance. When testing 50 cells for each subject, fewer than 2 cells expressed a fragile site, the result was considered a negative result. Various fra (X) expression (P) levels in the cell population