Evidence of clinical and genetic heterogeneity in autosomal dominant congenital cerulean cataracts

Autosomal dominant cerulean cataracts (ADCC) have previously been mapped to two loci: one on chromosome 17q24 and the other on chromosome 22q11.2–q12.2, which includes the ß-B2 crystallin (CRYBB2) candidate gene. Using polymorphic markers in these regions (D17S802, D17S836, D17S1806 and CRYBB2, D22S258) for linkage analysis, we excluded these loci in a large Moroccan family presenting with an unusual form of ADCC with early onset of lens opacities and rapid evolution. This finding confirms the clinical and genetic heterogeneity of autosomal dominant congenital cerulean cataracts.     

先天性膜性白内障一家系致病基因的遗传分析

目的 分析一个先天性白内障家系的遗传规律,对其突变基因进行初步研究.方法 选取一先天性膜性白内障家系,对家系成员进行临床检查并采集静脉血.标准饱和酚/氯仿抽提法提取DNA,选取多态性微卫星遗传标记,合成引物,聚合酶链反应,聚丙烯酰胺凝胶电泳,基因分型,等位基因共享分析法对已知候选基因进行排除性定位.结果 该家系为常染色体显性遗传性先天性白内障家系.其致病基因与D22S315联系紧密,重组发生在以D22S303和D22S1167为上下边界的范围内.对该范围内已知的先天性白内障致病基因CRYBB1、CRYBB2、CRYBB3、CRYBA4进行DNA直接测序,未发现突变.结论 该家系致病基因定位于22q11.2～q12.1的2.4 Mbp范围内,其致病基因与已知基因座不同.该范围内可能存在导致先天性膜性白内障的新的致病基因.     

常染色体显性遗传性先天性白内障一家系致病基因的初步定位

目的 初步定位常染色体显性遗传性先天性白内障(ADCC)一家系的致病基因。方法 收集ADCC一家系资料,在已知先天性白内障致病基因和位点附近,选择合适的短串联重复序列多态性标记(STRP),对ADCC一家系进行连锁分析,使用Mlink软件采用对数优势记分法(LOD)计算LOD值。结果 在STRP中,D17S805、D17S1294及D17S1293与致病基因位点连锁的最大LOD值分别为2．03、2．49及2．22(重组率0=0)。结论 该ADCC家系的致病基因初步定位在第17对染色体上;CRYBA1基因为候选基因。（中华眼科杂志,2004,40：824-827)     

Posterior polar cataract: genetic analysis of a large family

Congenital cataracts are clinically and genetically heterogeneous. Loci for autosomal dominant posterior polar cataracts have been mapped to chromosomes 1p36, 11q22-q22.3, 16q22, and 20p12-q12. We investigated a large four-generation family with 20 individuals affected with congenital posterior polar cataracts. After exclusion of known loci for posterior polar cataracts, a genome-wide screen was conducted. In this family, we mapped dominant congenital posterior polar cataracts to chromosome 10q24. On haplotype analysis, we identified an 11-cM interval between loci D10S1680 and D10S467, which included the PITX3 gene. On sequencing the coding region of PITX3, we found a 17-base-pair duplication in exon 4. Although the same genotype was described in a family with ASMD and cataracts, the common phenotype of this mutation is probably posterior polar cataract; a modifier gene is presumed to cause anterior segment abnormalities in the previously described patients. The same mutation was recently identified in four families with congenital cataracts. This study provides further evidence of genetic heterogeneity of autosomal dominant posterior polar cataract.     

Posterior Polar Cataract: Genetic Analysis of a Large Family

Congenital cataracts are clinically and genetically heterogeneous. Loci for autosomal dominant posterior polar cataracts have been mapped to chromosomes 1p36, 11q22-q22.3, 16q22, and 20p12-q12. We investigated a large four-generation family with 20 individuals affected with congenital posterior polar cataracts. After exclusion of known loci for posterior polar cataracts, a genome-wide screen was conducted. In this family, we mapped dominant congenital posterior polar cataracts to chromosome 10q24. On haplotype analysis, we identified an 11-cM interval between loci D10S1680 and D10S467, which included the PITX3 gene. On sequencing the coding region of PITX3, we found a 17-base-pair duplication in exon 4. Although the same genotype was described in a family with ASMD and cataracts, the common phenotype of this mutation is probably posterior polar cataract; a modifier gene is presumed to cause anterior segment abnormalities in the previously described patients. The same mutation was recently identified in four families with congenital cataracts. This study provides further evidence of genetic heterogeneity of autosomal dominant posterior polar cataract.     

Genetic heterogeneity of the Coppock-like cataract: a mutation in CRYBB2 on chromosome 22q11.2

PURPOSE: To identify the genetic defect for the Coppock-like cataract (CCL) affecting a Swiss family, which defect was unlinked to the chromosome 2q33-35 CCL locus. METHODS: A large family was characterized for linkage analysis by slit lamp examination or by the review of drawings made before cataract extraction. The affection status was attributed before genotyping, and the genotyping was masked to the affection status. Two-point and multipoint linkage analyses were performed using the MLINK and the LINKMAP components of the LINKAGE program package (ver. 5.1), respectively. Mutational analysis of candidate genes was performed by a combination of direct cycle sequencing and an amplification refractory mutation system assay. RESULTS: Ten individuals were affected with the CCL phenotype. The disease was autosomal dominant and appeared to be fully penetrant. A new CCL locus was identified on chromosome 22q11.2 within a 11.67-cM interval (maximum lod score [Zmax] = 4.14; theta = 0). Mutational analysis of the CRYBB2 candidate gene identified a disease-causing mutation in exon 6. This sequence change was identical with that previously described to be associated with the cerulean cataract, a clinically distinct entity. CONCLUSIONS: The CCL phenotype is genetically heterogeneous with a second gene on chromosome 22q11.2, CRYBB2. The CCL and the cerulean cataract are two distinct clinical entities associated with the same genetic defect. This work provides evidence for a modifier factor that influences cataract formation and that remains to be identified.     

A Novel CRYBB2 Missense Mutation Causing Congenital Autosomal Dominant Cataract in an Italian Family

Congenital cataract is a leading cause of visual impairment in children and brings approximately 10% of childhood blindness worldwide. Molecular analysis revealed ~60 loci to be associated with several phenotypes of childhood cataracts. Until now, more than 30 loci and 18 genes on different chromosomes have been associated with autosomal dominant congenital cataract (ADCC). Here, we present a three-generation Italian family with a non syndromic ADCC. A linkage analysis carried out using HumanCytoSNP-12 DNA Analysis BeadChip led us to identify ten genomic regions virtually involved in the disease. All the genes located in these regions were scored for possible relationship with ADCC and, according to a strict clinical and genetic selection, 4 genes have been analyzed. A novel sequence variant was found in the CRYBB2 gene (p.Ser143Phe). This variant affects a conserved aminoacid in the third Greek key motif of the protein, cosegregates with the disease phenotype in all affected individuals and is not present both in the unaffected family members and 100 healthy control subjects. Finally, we identified the first CRYBB2 mutation in an Italian family causing a clinical picture of ADCC.     

常染色体显性先天性白内障一家系致病基因的连锁分析

背景先天性白内障约1／3的病例是由遗传所致,已发现遗传性白内障有着极为明显的遗传异质性,了解先天性白内障的致病基因对其基因治疗极为重要。目的分析一个具有常染色体显性遗传特点的先天性白内障家系的临床表型特征,进行已知致病基因的筛查定位。方法对遗传性先天性白内障一家系共16名成员眼部进行详细的临床检查,包括6例患者,确定为本家系白内障患者的临床表型。收集其中11名家系成员的血液样本提取DNA,包括3名正常家系成员及其配偶、5例患者。利用连锁分析进行排除定位,并采用Schuelke报道的新方法,只合成普通引物及一种荧光标记的通用引物M13,进行聚合酶链反应（PCR）,对连锁区域内的候选基因进行基因序列分析。结果本家系的白内障遗传方式符合常染色体显性遗传特征。基因连锁分析表明,在D22S315得到最高LOD值为1．20,在D16S3068得到LOD值为0．6。CRYBB2基因所有编码区及外显子与内含子交界处未发现基因序列突变。结论本家系初步排除了CRYBB2基因与此家系先天性白内障的相关性。对这个家系的基因定位需要更进一步的全基因组扫描,以发现致病基因在染色体上的可疑区间。连锁分析中进行微卫星位点的PCR扩增时,利用合成荧光标记的通用引物M13,可以显著降低成本,并取得同样的实验结果。     

Autosomal dominant congenital cataract. Morphology and genetic mapping

We studied a large Danish pedigree with autosomal dominant congenital cataracts (ADCC) in 9 generations. Morphological characteristics of the cataracts are described and documented by photos. In contrast with several other types of ADCC the cataracts studied were progressive during infancy and childhood. Linkage analysis with 14 marker systems revealed close linkage between this Marner cataract locus (CAM) and the locus of Haptoglobin (HP) on chromosome 16. Genetic heterogeneity in ADCC has now established with the genetic mapping of cataract loci to chromosome 1, chromosome 2, and chromosome 16.     

Homozygous CRYBB1 deletion mutation underlies autosomal recessive congenital cataract

PURPOSE: Some 30% of cases of congenital cataract are genetic in origin, usually transmitted as an autosomal dominant trait. The molecular defects underlying some of these autosomal dominant cases have been identified and were demonstrated to be mostly mutations in crystallin genes. The autosomal recessive form of the disease is less frequent. To date, only four genes and three loci have been associated with autosomal recessive congenital cataract. Two extended unrelated consanguineous inbred Bedouin families from southern Israel presenting with autosomal recessive congenital nuclear cataract were studied. METHODS: Assuming a founder effect, homozygosity testing was performed using polymorphic microsatellite markers adjacent to each of 32 candidate genes. RESULTS: A locus on chromosome 22 surrounding marker D22S1167 demonstrated homozygosity only in affected individuals (lod score > 6.57 at theta = 0 for D22S1167). Two crystallin genes (CRYBB1 and CRYBA4) located within 0.1 cM on each side of this marker were sequenced. No mutations were found in CRYBA4. However, an identical homozygous delG168 mutation in exon 2 of CRYBB1 was discovered in affected individuals of both families, generating a frameshift leading to a missense protein sequence at amino acid 57 and truncation at amino acid 107 of the 252-amino-acid CRYBB1 protein. Denaturing [d]HPLC analysis of 100 Bedouin individuals unrelated to the affected families demonstrated no CRYBB1 mutations. CONCLUSIONS: CRYBB1 mutations have been shown to underlie autosomal dominant congenital cataract. The current study showed that a different mutation in the same gene causes an autosomal recessive form of the disease.     

东北地区一遗传性白内障家系的临床遗传学及基因定位研究

目的:分析一先天性核型白内障家系的遗传方式及致病基因所在位置。方法:收集一个3代遗传性白内障家系成员的临床资料;提取家系成员外周血DNA,选取62个态性微卫星标记进行连锁分析。应用LINKAGE软件(version 5.2)中的MLINK程序计算两点连锁LOD值,并人工构建家系成员的单体型。结果:确定该家系为一常染色体显性遗传性白内障大家系,在微卫星标记D22S689可获得最大LOD值2.71(θ=0时),单体型提示该家系表型可能与染色体22q11.2-12.1区域连锁。该区域含有CRYBB1,CRYBB2,CRYBB3,CRYBA44个候选基因。结论:本研究先天性核型白内障家系符合常染色体显性遗传规律,其致病基因定位于22q11.2-12.1区域。     

Mutations in betaB3-crystallin associated with autosomal recessive cataract in two Pakistani families

PURPOSE: To identify the disease locus for autosomal recessive congenital cataracts in consanguineous Pakistani families. METHODS: Two Pakistani families were ascertained, patients were examined, blood samples were collected, and DNA was isolated. A genome-wide scan was performed using >382 polymorphic microsatellite markers on genomic DNA from affected and unaffected family members. Two-point lod scores were calculated, haplotypes were formed by inspection, and candidate genes were sequenced. Real-time quantitative PCR techniques were used to determine the mRNA levels, and molecular modeling was performed to gain a better understanding of the significance of the disease-causing mutation. RESULTS: In the genome-wide scan, maximum lod scores of 2.67 and 2.77 for family 60004 and 2.02 and 2.04 for family 60006 were obtained for markers D22S539 and D22S315, respectively. The linked region, 22.7 cM (10 Mb) flanked by markers D22S420 and D22S1163, contains the beta-crystallin gene cluster including the genes CRYBA4, CRYBB1, CRYBB2, and CRYBB3. Sequencing of these genes showed a G-->C transition in exon 6 of CRYBB3 resulting in a p.G165R change in the betaB3-crystallin protein that cosegregates with the disease in both families. Real-time PCR analysis suggested that betaB3-crystallin mRNA levels approximate those of other betagamma-crystallins. Molecular modeling predicted changes in electrostatic potential that would be expected to reduce the stability of the fourth Greek-key motif, and hence the entire protein, dramatically. CONCLUSIONS: For the first time, a mutation in CRYBB3 is reported in two consanguineous Pakistani families with autosomal recessive congenital cataracts.     

A new locus for autosomal dominant congenital cataracts maps to chromosome 3

PURPOSE: To map a gene for cataracts in a family with congenital nuclear and sutural cataracts and to examine candidate genes in the linked region. METHODS: A large family with autosomal dominant congenital nuclear and sutural cataracts was identified and characterized. A genome-wide screen was conducted with a set of markers spaced at 10- to 15-cM intervals, and linkage was assessed using standard LOD score analysis. RESULT: Fifteen (15) affected individuals were identified. This form of congenital cataracts maps to a 12-cM region on chromosome 3q21.2-q22.3 between markers D3S3674 and D3S3612, with a maximum multipoint LOD score of 6.94 at D3S1273. The crystallin gene, CRYGS, was excluded as a candidate gene for this locus. CONCLUSIONS: There are now more than 12 different genetic loci that cause congenital cataracts. The most recent locus to be identified is on chromosome 3q21.2-q22.3, in a family with congenital nuclear and sutural cataracts.     

中国人常染色体遗传的病理性近视基因定位

目的在中国人群中进行病理性近视致病基因的定位。方法1个12人的病理性近视家系（患者7名）经过研究人员告知,同意参加本研究。从每个家系成员静脉血中提取DNA,选取覆盖全基因组的330对高度杂合的微卫星DNA引物,进行基因组扫描;以常染色体显性遗传为模式,基因频率0．0133和外显率100％的条件下,运用Linkage软件进行二点连锁分析,运用Genehunter软件进行多点连锁分析。标记位点之间的遗传距离根据Genethon连锁图谱来确定。基于最低重组率原则,用cyanic软件构建单倍型。结果二点连锁分析发现15号染色体长臂上存在与病理性近视密切连锁的位点。在重组率为0的情况下,最大对数优势记分（LOD）值1．76出现在D15S1010,D15S1007和D15S1042位点;多点连锁分析也支持这个区域内存在连锁,最大NIL值为5．16。单倍型分析把这个近视眼位点局限在15q12-13上D15S1019和D15S146之间大约12cM的区间内。在已知的近视眼相关位点,包括18p11．31,12q21-23,7q36,17q21-22,4q22-q27,2q37．1,15q15-21,12q13．11-13．2,6p21．3,1q21-31,1p21和21q22．3,均没有发现明确的连锁证据。结论在15q12-13可能存在一个新的近视眼基因位点。在这个区域内至少有94个已知的基因,因此有必要对此区域进行测序寻找致病基因,这个新的基因位点的发现也证实了病理性近视存在很强的遗传异质性。     

Genetically distinct autosomal dominant posterior polar cataract in a four-generation Japanese family

PURPOSE: To describe the clinical findings of a form of posterior polar cataract in a large Japanese family and to determine whether the posterior polar cataract is causally related to other autosomal dominant cataracts with known genes, chromosomal locations, or both. METHODS: Systemic and ocular histories were obtained and comprehensive ophthalmic examinations were performed in 15 of 37 members of the Japanese family. The posterior polar cataract was transmitted in an autosomal dominant manner through four generations. Although there is some variation in the degree of opacification, the posterior polar cataract in this family is characterized by progressive disk-shaped posterior subcapsular opacities. Genetic linkage analysis was performed with 41 polymorphic microsatellite markers located in chromosomal regions known for linkage to cataracts. Genomic DNA extracted from the 15 individuals was amplified by polymerase chain reaction, the genotype at the marker loci was determined in each family member, and the lod score was calculated at each locus. RESULTS: Significant linkage of the posterior polar cataract was ruled out from the following 10 loci or chromosomal regions: 16q22 and 1p36, to which two forms of autosomal dominant posterior polar cataract have been assigned: 1q21-q25, 2q33-q35, 13cen, 17p13, 17q11-q12, 17q24, 21q22, and 22q, which are the regions responsible for other autosomal dominant congenital cataracts. CONCLUSIONS: This study confirms the genetic heterogeneity of autosomal dominant posterior polar cataracts and demonstrates that the posterior polar cataract in this Japanese family is phenotypically and genetically distinct from previously mapped cataracts.     

Identification of a novel locus on 2q for autosomal dominant high-grade myopia

PURPOSE: Myopia, or nearsightedness, is a visual disorder of high and growing prevalence in the United States and in other countries. Pathologic high myopia, or myopia of 相似文献   

Age-related maculopathy: an expanded genome-wide scan with evidence of susceptibility loci within the 1q31 and 17q25 regions.

PURPOSE: We seek to identify genetic loci that contribute to age-related maculopathy susceptibility. METHODS: Families consisting of at least two siblings affected by age-related maculopathy were ascertained using eye care records and fundus photographs. Additional family members were used to increase the power to detect linkage. Microsatellite genotyping was conducted by the National Heart, Lung and Blood Institute Mammalian Genotyping Service and the National Institutes of Health Center for Inherited Disease Research. Linkage analyses were conducted with parametric (autosomal dominant; heterogeneity lod score) and nonparametric methods (S(all) statistic) using three diagnostic models. False-positive rates were determined from simulations using actual pedigrees and genotyping data. RESULTS: Under our least stringent diagnostic model, model C, 860 affected individuals from 391 families (452 sib pairs) were genotyped. Sixty-five percent of the affected individuals had evidence of exudative disease. Four regions, 1q31, 9p13, 10q26, and 17q25, showed multipoint heterogeneity lod scores or S(all) scores of 2.0 or greater (under at least one model). Under our most stringent diagnostic model, model A, the 1q31 heterogeneity lod score was 2.46 between D1S1660 and D1S1647. Under model C, the 17q25 heterogeneity lod score at D17S928 was 3.16. Using a threshold of 1.5, additional loci on chromosomes 2 and 12 were identified. CONCLUSIONS: The locus on chromosome 1q31 independently confirms a report by Klein and associates mapping an age-related maculopathy susceptibility gene to this region. Simulations indicate that the 1q31 and 17q25 loci are unlikely to be false positives. There was no evidence that other known macular or retinal dystrophy candidate gene regions are major contributors to the genetics of age-related maculopathy.     

Endothelial dystrophy,iris hypoplasia,congenital cataract,and stromal thinning (edict) syndrome maps to chromosome 15q22.1-q25.3

PURPOSE: To localize a gene causing a newly described autosomal dominant anterior segment dysgenesis characterized by corneal endothelial dystrophy, iris hypoplasia, congenital cataracts, and corneal stromal thinning (EDICT syndrome).DESIGN: Experimental study.METHODS: A set of microsatellite markers spanning the 22 human autosomes was used to perform linkage analysis on affected and unaffected individuals within a single family.RESULTS: Linkage analysis of the anterior segment dysgenesis endothelial dystrophy, iris hypoplasia, congenital cataract, and stromal thinning (EDICT) syndrome in this family revealed a logarithm of the odds (LOD) score of 2.71 on chromosome 15q22.1-25.3 between markers D15993 and D15S202. These results suggest a gene for EDICT syndrome lies in this chromosomal region.CONCLUSIONS: A LOD score of 2.71 suggests a novel locus associated with the newly described EDICT syndrome lies in a region of chromosome 15 between markers D15S993 and D15S202. Identification of the disease-causing gene in this region may yield insights into a broad range of disorders affecting the corneal stroma, endothelium, iris, and lens.     

遗传性先天性核性白内障家系CRYAB错义突变

目的 鉴定一个四代常染色体显性遗传性先天性白内障(autosomaldominant congenital cataract,ADCC)家系的致病基因.方法 收集ADCC一家系资料,全面检查,提取血液DNA,在已报道的与先天性白内障相关的致病基因和其附近选择合适的微卫星标记位点进行连锁分析,对提示连锁的染色体区域内的已知候选基因测序.结果 系谱图分析示该ADCC家系符合常染色体显性遗传特点.裂隙灯显微镜检查示全部患者表型均为核性.连锁分析示致病基因定位在11q22.3-23.1区域内,对此区域内的候选基因B-晶状体蛋白基因进行测序,发现其外显子1第58位核苷酸C→T错义突变,引起所编码的第20位脯氨酸被丝氨酸取代(p20S).结论 B-晶状体蛋白的点突变导致了该家系遗传性先天性核性白内障,丰富了基因型-表型谱,并为分子机制的研究提供了新线索.     

一个先天性白内障家系基因突变热点分析报告

目的：对一个来自广东兴宁的四代先天性白内障家系进行常染色体显性基因突变热点的分析，了解这个家系在热点上是否有相应的改变。方法：该家系19名成员(包括患者8人，非患者11人)知情同意进入本研究。8例患者在中山眼科中心接受全面的眼部及全身检查．以排除存在白内障以外眼部及全身疾患。11例非患病亲属仅接受眼部检查。对这19例研究对象各抽取外周血5ml，提取基因组DNA。针对国外文献报道(截至2003年1月为止)的与常染色体显性遗传先天性白内障相关的10个基因(CRYAA、CRYAB、CRYBA1／A3、CRYGD、GJA8、CRYGC、CRYBB2、GJA3、MIP及BFSP2)的17个突变热点，设计引物使聚合酶链反应扩增的片段覆盖这17个位点，对扩增产物进行测序和序列分析，了解这19名研究对象在17个突变热点上是否有相应的序列改变。结果：19例研究对象，在国外文献报道的17个与常染色体显性遗传先天性白内障相关的突变热点，均未发现相应的序列改变。结论：初步排除这个常染色体显性遗传先天性白内障家系与国外文献报道的17个突变热点相关。