散发Rett综合征患儿新生MECP2突变亲源鉴定和X染色体失活15例分析  

Analysis of the parental origin of de novo MECP2 mutations and X chromosome inactivation in fifteen sporadic cases with Rett syndrome

作　　者：朱兴旺[1] 潘虹[1] 李美蓉[1] 包新华[1] 张晶晶[1] 吴希如[1] 

机构地区：[1]北京大学第一医院儿科,100034

出　　处：《中华儿科杂志》2009年第8期565-569,共5页Chinese Journal of Pediatrics

摘　　要：目的了解Rett综合征（RTT）患儿致病基因甲基化CpG结合蛋白2基因（MECP2）的突变亲源起源和X染色体失活（XCI）的影响。方法选取15例临床典型RTT并经DNA测序证实存在新生MECP2突变和一个已知单核苷酸多态性位点的患儿，分别对患儿及父母外周血DNA进行等位基因特异性PCR扩增，通过DNA测序和凝胶电泳判定患儿突变的亲源起源；用雄激素受体基因（AR）的三核苷酸多态性进行基因型分析判定XCI是否发生偏斜和失活X染色体的亲源性。结果15例RTT患儿中13例是由于C→T碱基转换引起的点突变，2例为移码突变。13例点突变患儿的突变全部来自父源，2例移码突变中1例突变来自父源，另外1例来自母源。突变来自父源的RTT患儿占选取病例总数的93．3％；XCI分析除2例由于无AR多态性信息无法判定外，其余13例中有8例XCI为随机失活，5例为非随机失活。5例非随机失活的患儿均表现为父源X染色体优先失活。结论散发RTT患儿新生MECP2突变几乎全部来自其父源X染色体，XCI多为随机失活，部分非随机失活均表现为其父源X染色体优先失活。Objective Rett syndrome （RTF） is a neurodevelopmental disorder occurring almost exclusively in females as sporadic cases due to de novo mutations in the methyl-CpG-binding protein 2 gene （MECP2）. Familial cases of RTT are rare and are due to X-chromosomal inheritance from a carrier mother. Recently, DNA mutations in the MECP2 have been detected in approximately 84. 7% of patients with RTT in China. To explain the sex-limited expression of RTT, it has been suggested that de novo X-linked mutations occur exclusively in male germ cells resulting therefore only in affected daughters. To test this hypothesis, we have analyzed the parental origin of mutations and the XCI status in 15 sporadic cases with RTT due to MECP2 molecular defects. Methods Allele-specific PCR was performed to amplify a fragment including the position of the mutation. The allele-specific PCR products were sequenced to determine which haplotype contained the mutation. It was then possible to determine the parent of origin by genotyping the single nucleotide polymorphism （SNP） in the parents. The degree of XCI and its direction relative to the X chromosome parent of origin were measured in DNA prepared from peripheral blood leucocytes by analyzing CAG repeat polymorphism in the androgen receptor gene （AR）. Results Except for 2 cases who had a frameshift mutation; all the remaining 13 cases had a C→T transition mutation. Paternal origin has been determined in all cases with the C→T transition mutation. For the two frameshift mutations, paternal origin has been determined in one case and maternal origin in the other. The frequency of male germ-line transmission in mutations is 93.3%. Except for 2 cases who were homozygotic at the AR locus, of the remaining 13 cases, 8 cases had a random XCI pattern; the other five cases had a skewed XCI pattern and they favor expression of the maternal origin allele. Conclusion De novo mutations in sporadic RTT occur almost exclusively on the paternally derived X chromosome and that this is most p

关 键 词：RETT综合征 X染色体失活 染色体畸变 基因 遗传 

分 类 号：R686[医药卫生—骨科学]