Tsongalis G J, Silverman L M
Department of Hospital Laboratories and Pathology, University of North Carolina Hospitals, Chapel Hill.
Arch Pathol Lab Med. 1993 Nov;117(11):1121-5.
Fragile X syndrome is the most common form of familial mental retardation (one in 1250 males and one in 2500 females, characterized by prominent dysmorphic features, macro-orchidism, and varying degrees of mental retardation. Diagnosis of this syndrome has relied on cytogenetic demonstration of the fragile site at position Xq27.3. A gene associated with the fragile X syndrome, FMR-1, has been isolated and mapped to the region of the X chromosome that corresponds to the region of the fragile site. Expansion of a trinucleotide repeat, CGG, and abnormal methylation of a CpG island account for the majority of mutations identified in FMR-1. These molecular characteristics have greatly enhanced the identification of affected individuals and carriers of the premutation who were not detected cytogenetically.
脆性X综合征是最常见的家族性智力迟钝形式（男性发病率为1/1250，女性为1/2500），其特征为明显的畸形特征、巨睾症以及不同程度的智力迟钝。该综合征的诊断依赖于细胞遗传学对位于Xq27.3的脆性位点的证实。一个与脆性X综合征相关的基因FMR-1已被分离并定位到X染色体上与脆性位点区域相对应的区域。三核苷酸重复序列CGG的扩增以及CpG岛的异常甲基化是在FMR-1中鉴定出的大多数突变的原因。这些分子特征极大地提高了对那些细胞遗传学检测未发现的受影响个体和前突变携带者的识别能力。
