de Vries B B, Halley D J, Oostra B A, Niermeijer M F
Department of Clinical Genetics, University Hospital Dijkzigt and Erasmus University, Rotterdam, The Netherlands.
J Med Genet. 1998 Jul;35(7):579-89. doi: 10.1136/jmg.35.7.579.
The fragile X syndrome is characterised by mental retardation, behavioural features, and physical features, such as a long face with large protruding ears and macro-orchidism. In 1991, after identification of the fragile X mental retardation (FMR1) gene, the cytogenetic marker (a fragile site at Xq27.3) became replaced by molecular diagnosis. The fragile X syndrome was one of the first examples of a "novel" class of disorders caused by a trinucleotide repeat expansion. In the normal population, the CGG repeat varies from six to 54 units. Affected subjects have expanded CGG repeats (>200) in the first exon of the FMR1 gene (the full mutation). Phenotypically normal carriers of the fragile X syndrome have a repeat in the 43 to 200 range (the premutation). The cloning of the FMR1 gene led to the characterisation of its protein product FMRP, encouraged further clinical studies, and opened up the possibility of more accurate family studies and fragile X screening programmes.
脆性X综合征的特征包括智力迟钝、行为特征和身体特征，如长脸、大耳朵突出以及巨睾症。1991年，在脆性X智力迟钝（FMR1）基因被鉴定出来后，细胞遗传学标记（Xq27.3处的一个脆性位点）被分子诊断所取代。脆性X综合征是由三核苷酸重复扩增引起的一类“新型”疾病的首批例子之一。在正常人群中，CGG重复序列从6个到54个单位不等。受影响的个体在FMR1基因的第一个外显子中具有扩增的CGG重复序列（>200）（完全突变）。脆性X综合征表型正常的携带者在43到200范围内有重复序列（前突变）。FMR1基因的克隆导致了其蛋白质产物FMRP的特性鉴定，鼓励了进一步的临床研究，并为更准确的家系研究和脆性X筛查项目开辟了可能性。
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