Objective To analyze the genetic characteristics and molecular mechanism of Chinese patients with Rett syndrome (RTT) and assess the recurrent risk in order to provide genetic counseling for the family with RTT patient.Methods Methyl-CpG-binding protein 2 (MECP2) gene mutation analysis were performed on 405 Chinese RTT cases and 292 mothers of the patients with MECP2 mutations with polymerase chain reaction (PCR),direct sequencing and multiplex ligation-dependent probe amplification (MLPA).Then cyclin-dependent kinase-like 5 (CDKL5) and forkhead box protein G1 (FOXG1) genes mutation analysis were performed on the patients without MECP2 mutation.Parental origin of mutated MECP2 gene was detected with allele specific PCR analysis.Based on the difference methylation in CpG island of the first exon of human androgen-receptor gene on active and inactive X-chromosomes,methylation sensitive restriction endonuclease digestion was used to analyze the X-chromosome inactive (XCI) patterns.Results MECP2 gene mutation was found in 86.9％ RTT cases.CDKL5 gene mutation was found in only 3 cases with early-onset seizures variant.No FOXG1 mutation was found.There were 94.4％ MECP2 mutations of paternal origin,and point mutations were common.However,microdeletions were common in maternal origin mutation.MECP2 gene mutation was found in only 1 (0.34％,1/292) mother with normal phenotype and non-random XCI pattern.Her daughter was a RTT patient with preserved speech variant,and her XCI pattern was random.Conclusion MECP2 is the main pathogenic gene in RTT.CDKL5 gene should be screened in patients with early-onset seizures variant without MECP2 gene mutation.The majority of RTT patients had paternally derived de novo MECP2 gene mutation,which may explain the high female to male ratio in RTT.Only 0.34 ％ mothers carried the pathogenic mutation,indicating a lower recurrent risk for RTT families,The XCI may modulate the phenotype of RTT,so MECP2 gene mutation screening in the mothers is important for genetic counseling.%目的 通过对我国Rett综合征(Rett syndrome,RTT)患者的系统研究,了解我国RTT的遗传特点以评估再发风险,为患者家庭提供遗传咨询.方法 应用聚合酶链式反应、DNA测序、多重连接依赖探针扩增技术对405例RTT患儿的甲基化CpG结合蛋白2(methyl-CpG-binding protein2,MECP2)基因、细胞周期蛋白依赖激酶样5 (cyclin-dependent kinase-like 5,CDKL5)基因及FOXG1 (forkhead box protein G1)基因进行突变分析；应用等位基因特异性PCR分析患儿MECP2基因突变来源；对292例患儿的母亲进行MECP2基因突变分析；根据在有活性与失活X染色体上雄激素受体第1个外显子甲基化的不同,应用甲基化敏感限制性内切酶分析X-染色体失活类型(X-chromosome inactive pattern,XCI),观察其对RTT表型的影响.结果 MECP2突变在我国RTT患儿中的检出率为86.9％(352/405),仅发现3例早发惊厥型RTT患儿具有CDKL5突变,未发现FOXG1基因突变.94.4％(85/90)的MECP2突变位于父亲来源的X染色体上,以点突变为主要类型,占90.6 ％(77/85).80％的母源突变为小缺失.仅1例(0.34％,1/292)表型正常母亲携带致病突变,其XCI呈高度非随机失活,女儿为保留语言型不典型RTT,XCI呈随机失活.结论 MECP2为我国RTT的主要致病基因,早发惊厥型RTT患儿MECP2基因突变筛查阴性者,应进行CDKL5基因突变分析.MECP2突变以父源新生突变为主,可以解释RTT患儿中女孩多于男孩的遗传特点.母亲突变携带率仅为0.34％,提示RTT再发风险较低.由于X染色体非随机失活可使携带MECP2基因突变的女性具有正常表型,因此对表型正常的患儿母亲进行基因突变筛查,有利于对RTT家庭提供遗传咨询.
展开▼
