[英文释义] A condition characterized genotypically by mutation of the distal end of the long arm of the X chromosome (at gene loci FRAXA or FRAXE) and phenotypically by cognitive impairment,hyperactivity,SEIZURES,language delay,and enlargement of the ears,head,and testes. MENTAL RETARDATION occurs in nearly all males and roughly 50% of females with the full mutation of FRAXA. (From Menkes,Textbook of Child Neurology,5th ed,p226)
The screnning and prenatal gene dignosis for fragile x syndrome using pfu dna 综合征的筛查和产前基因诊断
fragile x syndrome ( fxs ) is the most common form of inherited mental retardation after down syndrome . it affects approximately 1 in 4000 males and 1 in 8000 females in the general population 脆性x综合征(fragilexsyndrome,fxs)是导致遗传性智力低下的主要原因之一,发病率仅次于先天愚型,在男性中的发病率约为1/4000,在女性中发病率约为1/8000。
To detect the patients and carriers of the fragile x syndrome, various analytic methods could be used . one is cytogenetic diagnosis to observe the expression of the fragile site fraxa located at xq27.3 对脆x综合征的诊断,可以通过细胞遗传学方法观察分析x染色体相应脆性位点的表达情况,或是通过southern印迹杂交的方法直接分析cgg重复的扩增突变。
The absence of the fmr1 gene product, fragile x mental retardation protein ( fmrp ), is believed to be responsible for the typical physical and mental characteristics of the fragile x syndrome . alleles with between 43 and 200 cgg repeats are called permutation . they are generally unmethylated with normal transcript and protein level, but are extremely unstable during transmission to next generation 带有前突变(n=43200)的个体其fmr1基因通常不会甲基化,可以正常转录和翻译产生fmrp,故没有临床表型出现,但是,在向下一代传递的过程中却是非常不稳定的,会从前突变扩增成为全突变。