A missense mutation S228P in the CRYBB1 gene causes autosomal dominant congenital cataract

Background Congenital cataract is a highly heterogeneous disorder at both the genetic and phenotypic levels. This study was conducted to identify disease locus for autosomal dominant congenital cataracts in a four generation Chinese family. Methods Family history and clinical data were recorded. All the members were genotyped with microsatellite markers which are close to the known genetic loci for autosomal congenital cataracts. Two-point Lod scores were obtained using the MLINK of the LINKAGE program package （vet 5.1）. Candidate genes were amplified by polymerase chain reaction （PCR） and direct cycle sequencing. Results The maximum Lod score of Zmax=2.11 was obtained with three microsatellite markers D22S258, D22S315, and D22S1163 at recombination fraction θ= 0. Haplotype analysis showed that the disease gene was localized to a 18.5 Mbp region on chromosome 22 flanked by markers D22S1174 and D22S270, spanning the β-crystallin gene cluster. A c.752T→C mutation in exon 6 of CRYBB1 gene, which resulted in a heterozygous S228P mutation in predicted protein, was found to cosegregate with cataract in the family. Conclusions This study identified a novel mutation in CRYBB1 gene in a Chinese family with autosomal dominant congenital cataract. These results provide strong evidence that CRYBB1 is a pathogenic gene for congenital cataract.     

Molecular genetic analysis of autosomal dominant late-onset cataract in a Chinese Family

Congenital cataract is a highly heterogeneous disorder at both the genetic and the clinical-phenotypic levels.A unique cataract was observed in a 4-generation Chinese family,which was characterized by autosomal dominant inheritance and late-onset.Mutations in the 13 known genes (CRYAA,CRYAB,CRYBB1,CRYBB2,CRYGC,CRYBA1/A3,CRYGD,Connexin50,Connexin46,intrinsic membrane protein LIM2,cytoskeletal protein BFSP2,the major intrinsic protein-MIP and the heat shock factor HSF4) have previously been demonstrated to be the frequent reason for isolated congenital cataracts,but the exact molecular basis and underlying mechanisms of congenital cataract still remain unclear.This study was designed to find whether these 13 genes developed any mutation in the family members and to identify the disease-causing gene.Polymerase chain reaction (PCR) and direct DNA sequence analysis were carried out to detect the 13 genes.The results showed that no mutation causing amino acid alternations was found in these potential candidate genes among all patients in the family,and only several single-nucleotide polymorphisms (SNPs) were identified.A transitional mutation in the fourth intron of CRYBB2 and some silent mutations in the first exon of BFSP2 and CRYGD were found in the cataract family,but further study showed that these mutations could also be found in normal controls.It was concluded that some unidentified genes may underlie the occurrence of late-onset cataract in this family.A genome-wide screening will be carried out in the next study.     

R25G mutation in exon 1 of LMNA gene is associated with dilated cardiomyopathy and limb-girdle muscular dystrophy 1B

Background Mutations of the LMNA gene encoding lamin A and C are associated with dilated cardiomyopathy （DCM）, conduction system defects and skeletal muscle dystrophy. Here we report a family with a mutation of the LMNA gene to identify the relationship between genotype and phenotype. Methods All 30 members of the family underwent clinical and genetic evaluation. A mutation analysis of the LMNA gene was performed. All of the 12 exons of LMNA gene were extended with polymerase chain reaction （PCR） and the PCR products were screened for gene mutation by direct sequencing. Results Ten members of the family had limb-girdle muscular dystrophy （LGMD） and 6 are still alive. Two patients suffered from DCM. Cardiac arrhythmias included atrioventricular block and atrial fibrillation; sudden death occurred in 2 patients. The pattern of inheritance was autosomal dominant. Mutation c.73C〉G （R25G） in exon 1 encoding the globular domains was confirmed in all of the affected members, resulting in the conversion of arginine （Arg） to glycine （Gly）. Conclusions The mutation R25G in exon 1 of LMNA gene we reported here in a Chinese family had a phenotype of malignant arrhythmia and mild LGMD, suggesting that patients with familial DCM, conduction system defects and skeletal muscle dystrophy should be screened by genetic testing for the LMNA gene.     

GJB2 (Cx26) gene mutations in Chinese patients with congenital sensorineural deafness and a report of one novel mutation

Background Mutations in GJB2 gene are a major cause of autosomal recessive congenital hearing loss and the cause in some rare cases of the autosomal dominant form. The purpose of this study was to investigate the frequency and the features of GJB2 mutations in the Chinese patients with congenital sensorineural deafness.Methods Using PCR amplifying the entire coding region of GJB2 gene and direct DNA sequencing to analyze mutations in this gene among unrelated 69 cases with autosomal recessive congenital nonsyndromic deafness and 27 cases of dominant congenital deafness and 35 sporadic cases. We also detected mutations in GJB2 in 100 control subjects with normal hearing.Results 17. 4% (12/69) of the probands in the autosomal recessive, 7. 4% (2/27) of dominant families and 5.7% ( 2/35 ) of the sporadic congenital deafness patients had deafness-causing mutations in GJB2, respectively. Nine types of the mutations in GJB2 were detected in the recessive and sporadic group. They consisted of five types of polymorphism, and four types of deafness-causing mutation with homozygous 35delG in 1 sporadic (1/35), and 235delC frameshift mutation in 1 sporadic (homozygotes) and 10 recessive patients (2 heterozygotes and 8 homozygotes), and homozygous 442G→A missense mutation and homozygous 465T→A nonsense mutation in 1 different recessive proband, respectively. The 465T→A that related to recessive deafness was a novel mutation found by this study. The homozygous (10/69, 14. 5%) and the heterozygous (2/69,2.9%) GJB2 mutation in the recessive patients (12/69, 17.4%) and the homozygotes in the sporadic patient (2/35, 5. 7%) all had congenital severe to profound sensorineural hearing loss.511G→A missense mutation and 299 -300delAT frameshift mutation were found in two autosomal dominant congenital deafness families (2/27, 7.4%). The total mutation frequency of GJB2 was 12.2% (16/131) in the Chinese patients with congenital sensorineural deafness and 235delC was the most common deafness-causing mutation. Six types of mutation-5 types of polymorphism and 1 type of heterozygous deletion (235delC) mutation were found in the 100 control subjects. The carry rate of the most frequent type of mutation 235delC was 0. 5% in the controls(1/200 alleles). 109G→A was the most frequent (15/100, 15%) and 79G→A was the second common (8/100, 8%) polymorphism in this population.Conclusions The general mutation rate of GJB2 is 12.2% (16/131) and the 235delC is the most common type of deafness-causing mutation in Chinese patients with congenital hearing loss. 465T→A nonsense mutation that is associated to autosomal recessive deafness is a novel mutation found by this screening. 511G→A and 299-300delAT mutations contribute to autosomal dominant hearing loss. The study further supports the view that the common types of mutation in GJB2 according to different ethnic background and that the mutation prevalence in the East Asian deafness population is lower than that in the white population.     

Misdiagnosis induced intraocular lens dislocation in anterior megalophthalmos

Anterior megalophthalmos (AM) is an uncommon developmental anomaly of the anterior segment of the eye with a constellation of findings that includes enlarged cornea, deep anterior chamber, posterior positioning of the iris and lens, iris stroma atrophy, hypoplasia of iris dilator, pupil displacement, large capsular bag, lens subluxation, prematurely cataract and the tendency to retinal detachment. AM, especially when symptoms are mild, is not an easy disease to diagnose. We present 3 AM cases that were misdiagnosed as congenital cataract with weak zonule and megalocornea. Intraocular lenses (IOLs) dislocated after standard cataract surgeries and subsequent surgery (replacing the dislocated IOLs with iris-claw intraocular lenses) achieved satisfactory outcome. Although rare, AM should be included in the differential diagnosis of enlarged cornea and we recommend implanting Artisan lens in AM patients.

     

Mutation analysis of p63 gene in the first Chinese family with ADULT syndrome

Background ADULT syndrome （acro-dermato-ungual-lacrimal-tooth syndrome） is a rare ectodermal dysplasia disorder known as autosomal dominant inheritance. Recent studies have linked p63 gene mutation to the development of this disease. However, the genetic characteristics of ADULT syndrome were still not well understood. Methods Mutation analysis of p63 gene in the first Chinese ADULT syndrome family was performed using direct DNA sequencing. Results The sequence analysis of exon 8 of p63 gene disclosed a heterozygous G〉A substitution at nucleotide 893 （R298Q） in the proband. In addition, a single nucleotide polymorphism （SNP） rs16864880 in the downstream flanking region （DFR） of p63 exon 8 was also identified in this family. The proband and the paternal side including her father exhibited the C/G genotype at this position. The C/G variant frequency in the paternal was significantly higher as compared with the maternal （6/10 vs 0/6, P=0.034）. Conclusions ADULT syndrome may be caused by the p63 gene mutation, and it might have closer genetic association with the paternal side in this family.     

Genetic characterization and protein stability analysis of a Chinese family with Von Hippel-Lindau disease

Background Von HippeI-Lindau disease （VHL）,a heritable autosomal dominant disease characterized by neoplasia in multiple organ systems,has rarely been reported in Asia.We genetically investigated a unique Chinese family with VHL disease and performed an analysis of the VHL protein stability.Methods Genomic deoxyribonucleic acid （DNA） extracted from peripheral blood was amplified by polymerase chain reaction （PCR） to three exons of the VHL gene in 9 members of the Chinese family with VHL disease.PCR products were directly sequenced.We estimated the effects of VHL gene mutation on the stability of pVHL,which is indicated by the free energy difference between the wild-type and the mutant protein （△△G）.Results The Chinese family was classified as VHL type 1.Three family members,including two patients and a carrier,had a T to G heterozygotic missense mutation at nucleotide 515 of the VHL gene exon 1.This missense mutation resulted in the transition from leucine to arginine in amino acid 101 of the VHL protein.There was low stability of the VHL protein （the △△G was 12.71 kcal/mol） caused by this missense mutation.Conclusions We first reported a family with this VHL gene mutation in Asia.This missense mutation is predicted to significantly reduce the stability of the VHL protein and contribute to the development of the renal cell carcinoma （RCC） phenotype displayed by this family.The genetic characterization and protein stability analysis of families with VHL disease are important for early diagnosis and prevention of the disease being passed on to their offspring.     

CLINICAL AND GENETIC ANALYSIS OF THREE FAMILIES WITH FAMILIAR AMYLOID POLYNEUROPATHY

Objective To study the clinical and genetic features of familiar amyloid polyneuropathy （FAP）.
Methods Three families of suspected FAP in China mainland and Macau were investigated on aspects of clinical manifestations, histological features, and gene analysis.
Results All the 3 families had the clinical features of sensory and motor polyneuropathies, and notable vegetative nerve involvements. Affected cases of one family had ultrasound proved cardiomyopathy. Histological studies showed amyloid deposition in all the biopsy tissues of the affected cases of the 3 families, and anti-transthyretin antisera staining was positive in 3 cases of one family. Gene analysis confirmed that mutation types were amyloidogenic transthyretin （ATTR） Val30Met, Phe33Val, and Gly67Glu in the 3 families respectively. The ATTR Gly67Glu family had a shorter survival time due to the heart involvement compared with the other 2 families.
Conclusion FAP is an autosomal dominant inherited disease, with its clinical manifestations related to the type of genetic mutation.     

Mutation analysis of PAX6 gene in a large Chinese family with aniridia

Background Mutations in PAX6 gene have been shown to be the genetic cause of aniridia, which is a severe panocular eye disease characterised by iris hypoplasia. However, there is no study to do genetic analysis of aniridia, although there are several case reports in China. Here, we describe a mutation analysis of PAX6 in a large Chinese family with aniridia.Methods Genomic DNA from venous blood samples was prepared. Haplotype analysis was performed with two genetic markers (D11S904 and D11S935 ). Fourteen exons of the PAX6 gene were amplified from genomic DNA. Polymerase chain reaction (PCR) products of each exon were analysed by single strand conformational polymorphism (SSCP). The PCR products having an abnormal pattern were sequenced to confirm the mutation.Results Significant evidence for allele sharing in affected patients was detected suggesting that PAX6 mutation links to aniridia in this family. An extra band corresponding to exon 9 in PAX6 was found by single strand conformational polymorphism analysis in all the aniridia patients in this family, but not detected in the unaffected members. A mutation of C to T was detected by sequencing at the nucleotide 1080 that converts the Arg codon (CGA) to the termination codon (TGA).Conclusions Aniridia is caused by a nonsense mutation of PAX6 gene in the large Chinese kindred. Genetic test is important to prevent the transmission of aniridia to their offsprings in the kindred by prenatal diagnosis.     

两个常染色体显性遗传先天性白内障家系突变热点筛查

[目的]对2个常染色体显性遗传先天性白内障中国家系进行基因突变热点筛查,以了解这两个家系的先天性白内障是否与文献报道的17个突变热点相关.[方法]对两个家系共20名成员(包括患者11人,非患者9人)抽取外周血提取基因组DNA,针对截至2003年1月为止国外文献报道的与常染色体显性遗传先天性白内障发病相关的10个基因上的17个突变热点,包括CRYAA(ARG116CYS),CRYAB(del450A),CRYBA1(EX3-4 DEL),CRYBB2(GLN155TER),CRYGC(THR5PRO,5-BP DUP at NT226),CRYGD(ARG14-CYS,PRO23THR,ARG58HIS,ARG36SER),GJA3(ASN63SER,PRO187LEU),GJA8(GLU48LYS,PRO88SER),BFSP2(ARG287TRP)及MIP(GLU134GLY,THR138ARG),设计引物使PCR扩增片段涵盖上述热点,对扩增产物进行序列分析,检测这11名患者在突变热点上是否有相应的序列改变.[结果]20名被检者的10个基因片段序列与GenBank发表序列相同,在17个突变热点均未发现相应基因突变.[结论]初步排除这个家系的先天性白内障与17个突变热点相关.     

GJA8基因错义突变致先天性白内障一家系遗传分析

  目的  通过使用外显子测序定位分析一先天性白内障家系中GJA8基因致病错义突变。  方法  对2020年6月在昆明医科大学第二附属医院就诊的一个先天性白内障家系全体成员进行详细的临床眼科检查及全身查体。采集先证者及6个亲属外周血并提取基因组DNA,应用全外显子测序筛查可疑致病基因,使用生物信息工具对可疑基因突变进行致病性分析,并对家系全部成员进行Sanger测序验证候选致病突变。  结果  外显子测序及生物信息学分析显示GJA8基因存在一个错义突变c.593G > A,p.R198Q,导致其第198位氨基酸残基由谷氨酰胺取代了原有的脯氨酸。氨基酸保守性分析显示该突变影响的氨基酸在物种间高度保守。在家系全部受检者中进行的Sanger测序结果表明该突变与疾病表型共分离,可以认定该突变是该突变为该家系的致病性突变,系谱分析显示该突变所致先天性白内障呈现常染色体显性遗传。  结论  位于GJA8基因的错义突变c.593G > A,p.R198Q是导致该家系出现先天性白内障的遗传病因,遗传方式为常染色体显性遗传。     

遗传性珊瑚状白内障突变晶状体蛋白分子构型及超微结构分析

目的:探讨珊瑚状遗传性白内障家系P23T突变的γD晶状体蛋白与病变晶状体结构的关系.方法:记录晶状体摘除术前的晶状体裂隙灯照片;应用SWISS-MODEL程序,建立人γD晶状体蛋白及其P23T突变体的计算机立体结构模型;透射和扫描电镜观测晶状体提取物.结果:蛋白立体结构模型分析发现,P23T的突变降低了蛋白最终分子总势能,使蛋白表面结构发生改变.电镜检查发现,白内障晶状体内有大小不等的结晶片和异常的卵圆形结构,晶状体上皮细胞出现裂解.结论:γD晶状体蛋白P23T突变体可能与晶状体内异常结晶片和晶状体上皮细胞的病理改变有关,其发生机制还有待分子动力学的研究.     

一个中国先天性有汗性外胚层发育不良家系的GJB6基因筛查

目的: 先天性有汗性外胚层发育不良是一种常染色体显性遗传病,GJB6基因突变与之相关。调查一个来自中国的先天性有汗性外胚层发育不良家系与GJB6基因的关系。方法: 收集一个共有17个家系成员(患者8人,5男3女)的先天性有汗性外胚层发育不良家系,采集家系成员的外周血,抽提DNA。然后针对GJB6基因的每个外显子设计引物,应用聚合酶链式反应(PCR)方法扩增GJB6基因的整个编码区,测序、筛查突变。结果: 通过对家系患者的GJB6基因筛查,发现了一个杂合错义突变c.31G>A(p.G11R)。结论: GJB6基因错义突变c.31G>A(p.G11R)导致该家系先天性有汗性外胚层发育不良。     

常染色体显性先天性白内障大家系致病基因定位的初步研究

目的:报道1个涉及5代17例患者的常染色体显性先天性白内障(ADCC)大家系,并进行致病基因的定位. 方法:对家系中8例患者进行眼科检查后明确临床表型,并提取所有血样的基因组DNA.首先对已报道的中国ADCC家系致病位点(9个基因的16个突变位点)进行DNA测序,然后根据已报道的17个ADCC候选基因和13个染色体区域,选取27个微卫星分子标记,应用LINKAGE软件进行连锁分析. 结果:8例患者均为先天性核性白内障.直接DNA测序未发现有已报道的中国家系基因突变.所选取的27个微卫星分子标记与该家系致病基因均不连锁. 结论:该ADCC家系致病基因不在已报道的17个ADCC候选基因和13个染色体区域,该家系中可能存在一个新的ADCC致病基因.     

良性家族性婴儿惊厥基因定位

目的：对5个中国良性家族性婴儿惊厥(benign familial infantile convulsion,BFIC)家系进行基因定位研究。方法：选择D19S245、D19S250、D16S3131、D16S3133、D2S399、D2S2330等6个STR作为DNA标记,应用聚合酶链反应(PCR),变性聚丙烯酰胺凝胶电泳(PAGE)和银染技术,采用LINKAGE软件包中的MLINK程序进行连锁分析。结果：在常染色体显性(AD)模式下,在标记位点D19S250处,家系2、3、5在重组率为0．000,外显率为90％时,获得最大两点对数优势计分值(log odds score,LOD)总和为2．151;在标记位点D16S3131处,家系2、5在重组率为0．085,外显率为70％、60％时,获得最大两点LOD值总和分别为1．056、1．155;在重组率为0．080,外显率为50％时,获得最大两点LOD值总和为1．227。提示这2个位点与BFIC疾病基因可能存在连锁关系。在其他位点处未获得提示连锁关系的信息。结论：部分BFIC家系的致病基因可能与D19S250或D16S3131存在连锁关系。     

PAX6基因R203X无义突变导致家族性先天无虹膜

目的探讨一个先天性无虹膜家系致病的分子基础。方法对一个先天性无虹膜家系进行全面的眼部检查,采集该家系的4例患者和两名健康成员外周静脉血,提取基因组DNA。采用DNA直接测序的方法分析无虹膜候选致病基因PAX6的14个外显子及其外显子-内含子拼接部的序列。结果该家系患者PAX6基因第8外显子存在一个杂合性突变c.C607T,导致编码蛋白在203位的精氨酸(p.R203X)处提前终止,产生一个变异蛋白;而家系正常成员未发现此突变,表型与突变位点呈共分离。结论 c.C607T(p.R203X)突变是PAX6基因导致无虹膜的突变热点之一,也存在于中国无虹膜家系中。