【作者】 何湘；

【导师】 王介东； 马旭；

【作者基本信息】 中国协和医科大学 ， 细胞生物学， 2008， 博士

【摘要】 先天性遗传性眼震是一类遗传异质性疾病,主要有常染色体显性遗传,常染色体隐性遗传和X连锁不完全显性遗传等三种遗传模式,但X连锁不完全显性遗传为先天性遗传性眼震的主要遗传模式,本文对6个不同的X连锁先天性遗传性眼震家系致病基因进行定位与突变分析及初步探讨X连锁不完全显性遗传的机制。目前仅发现一个先天性眼震的致病基因FRMD7,定位于X染色质上。FRMD7基因是FERM domain-containing 7基因,定位于Xq26-27,有12个外显子,编码的蛋白质属4.1蛋白超家族成员。本研究共收集了6个家系。对传递6代的X连锁先天性遗传性眼震家系进行连锁分析发现,微卫星分子标记DXS691和DXS1047与致病基因紧密连锁,检测到FRMD7基因第821位碱基由G变为T,导致编码271号氨基酸由半胱氨酸(cys)变为苯丙氨酸(phe)。对传递4代的X连锁先天性遗传性眼震家系进行连锁分析发现,微卫星分子标记DXSS691和DXS1047与致病基因紧密连锁,检测到FRMD7基因第1453,1454位碱基TG缺失,使425位后的氨基酸编码改变,氨基酸编码提前终止,在428位结束氨基酸编码。在剩余的四个家系中发现一个FRMD7基因多态性位点,位于FRMD7基因第7外显子656位碱基,碱基由G变为T,编码的氨基酸由甘氨酸变为缬氨酸。以上结果显示:由FRMD7基因突变造成X连锁先天性遗传性眼震占X连锁先天性遗传性眼震家系的33%(6个X连锁先天性遗传性眼震,有两个是由FRMD7基因突变引起)。在上述两个X连锁先天性遗传眼震家系部份女性携带者并不患病,表现为外显不全。为了探索X连锁不完全显性遗传可能发病机制,我们对第一个家系的女性携带者进行X染色质失活分析,结果表明在这个家系中不存在选择性的X染色质失活,所以选择性的X染色质失活不是造成该家系外显不全的原因。综上所述,我们的研究首次发现了携带有FRMD7的C271F基因突变和TG缺失的男性和部分女性有先天性遗传性眼震的临床表现。选择性的X染色质失活不是造成外显不全的原因。更多还原

【Abstract】 Congenital nystagmus(CN) is a common oculomotor disorder(frequency of 1/1,500 live births) characterized by bilateral involuntary,periodic,predominantly ocular oscillations.CN onset typically occurs at birth or within the first few months of life and occurs secondary to the genetic ocular diseases such as albinism,achromatopsia,and Leber congenital amaurosis(OMIN 204000).CN can be an idiopathic disease or associated with various diseases as a syndrome. The inheritance model is mainly X-linked idiopathic congenital nystagmus(XLICN),but autosomal recessive(OMIN 257400) and autosomal dominant(OMIN 164100,608345,193003) forms have been described.Some studies indicated that two disease loci of XLICN were mapped to Xq26-q27 and Xp11.4- Xp11.3.Recently, Tarpey et al.identified several mutations in FRMD7(OMIN 300628),a gene localizing to Xq26-q27 and responsible for a major part of XLICN.To identify the responsible gene for X-linked idiopathic congenital nystagmus (XLICN),the members of six XLICN families were recruited and were genotyped with microsatellite markers around the FRMD7 locus.Mutations were comprehensively screened by direct sequencing using gene specific primers.An X-inactivation pattern was investigated by X chromosome methylation analysis for different penetrance analysis. We found two different novel mutations of FRMD7 gene in two different XLICN families and found one SNP of FRMD7 gene.We analysis the X chromosome inactivation in the Shangdong family.We found the first mutation is a missense mutation of FRMD7 gene from Shangdong province XLICN family.The mutation is a transversion(c.812G＞T) in exon 9, which caused a conservative substitution of Cys to Phe at codon 271(p.C271F).This mutation cosegregated with all affected individuals and was present in the obligate, non-penetrant female carriers.However,the mutation was not observed in unaffected familial males or 400 control males.The locus of mutation located in conservated region of FRMD7gene.The second mutation in FRMD7 gene is a frame-shift mutation from Nanjing province XLICN family.The locus of mutation is c.1274-1275delTG(p.Glu426AlafsX4), which caused a frameshifi from codon 426 and subsequent premature truncation of the FRMD7 protein just two amino acids downstream(p.428X).Although this mutation is not in conservated region of FRMD7 gene,truncating mutations usually affect the stability of the mRNA.mRNA containing the mutation is highly unstable,and can be degraded by nonsense-mediated mRNA decay(NMD),the cartier would have nystagmus.In addition,we found one SNP in FRMD7 gene in other XLICN families.The SNP is a transversion(c.656G＞T) in exon 7.The result of X-inactivation analysis in Shangdong XLICN family indicated skewed X-inactivation is not the reason of the incomplete penetrance of female carriers in this family.Maybe there are other factors associated with this phenomenon.In conclusion,we have identified two novel mutations in FRMD7 gene for XLICN. And this finding will widen the mutation spectrum of the FRMD7 gene and confirm that FRMD7 plays an important role in motor control of eye movement.These findings also showed that mutation analysis of FRMD7 has a diagnostic value in Chinese XLICN families.更多还原