A new locus for autosomal recessive nuclear cataract mapped to chromosome 19q13 in a Pakistani family

PURPOSE: To identify the disease locus of autosomal recessive congenital nuclear cataracts in a consanguineous Pakistani family. METHODS: A large Pakistani family with multiple individuals affected by autosomal recessive congenital cataracts was 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, and haplotypes were formed by inspection. RESULTS: In the genome-wide scan, a maximum lod score of 2.89 was obtained for marker D19S414 on 19q13. Fine mapping using D19S931, D19S433, D19S928, D19S225, D19S416, D19S213, D19S425, and D19S220 markers from the Généthon database showed that markers in a 14.3-cM (12.66-Mb) interval flanked by D19S928 and D19S420 cosegregated with the cataract locus. Lack of homozygosity further suggests that the cataract locus may lie in a 7-cM (4.3-Mb) interval flanked by D19S928 proximally and D19S425 distally. On fine mapping, a maximum lod score of 3.09 was obtained with D19S416 at theta = 0. CONCLUSIONS: Linkage analysis identified a new locus for autosomal recessive congenital nuclear cataracts on chromosome 19q13 in a consanguineous Pakistani family.     

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)     

The telomere of human chromosome 1p contains at least two independent autosomal dominant congenital cataract genes

AIMS: Multiple genetic causes of congenital cataract have been identified, both as a component of syndromes and in families that present with isolated congenital cataract. Linkage analysis was used to map the genetic locus in a six generation Australian family presenting with total congenital cataract. METHODS: Microsatellite markers located across all known autosomal dominant congenital cataract loci were genotyped in all recruited family members of the Tasmanian family. Both two point and multipoint linkage analysis were used to assess each locus under an autosomal dominant model. RESULTS: Significant linkage was detected at the telomere of the p arm of chromosome 1, with a maximum two point LOD of 4.21 at marker D1S507, a maximum multipoint exact LOD of 5.44, and an estimated location score of 5.61 at marker D1S507. Haplotype analysis places the gene inside a critical region between D1S228 and D1S199, a distance of approximately 6 megabases. The candidate gene PAX7 residing within the critical interval was excluded by direct sequencing in affected individuals. CONCLUSION: This is the third report of congenital cataract linkage to 1ptel. The critical region as defined by the shared haplotype in this family is clearly centromeric from the Volkmann cataract locus identified through study of a Danish family, indicating that two genes causing autosomal dominant congenital cataract map to the telomeric region of chromosome 1p.     

特殊表型遗传性先天性白内障的超微结构和基因定位

目的 探讨一表型特殊、晶状体呈簇状混浊的常染色体显性遗传性先天性白内障(ADCC)的超微结构,并初步定位该疾病的相关候选基因。方法 收集特殊表型ADCC一家系资料,对家系成员行眼部检查;在光学显微镜和透射电镜下观察晶状体细胞超微结构的改变;选择γ-晶状体蛋白基因附近多个微卫星位点,对该家系ADCC疾病相关候选基因进行连锁分析。结果 光学显微镜下特殊表型ADCC患者晶状体纤维细胞失去正常排列规则,产生不规则折光,并可见网格样改变、黏液样变性及结晶样物质析出等局灶性退行性变;透射电镜下可见细胞皱缩、变形,失去正常长六边形形态,细胞间隙增宽,细胞内可见异常高密度球形颗粒沉着。连锁分析结果显示,该家系ADCC疾病相关候选基因与微卫星位点D2S2208、D2S2382及D2S164连锁,最大LOD值为3．34。结论 特殊表型ADCC的特异性病理学改变集中在晶状体纤维细胞,其疾病相关候选基因极可能为γ-晶状体蛋白基因。（中华眼科杂志,2004,40：306-310)     

一常染色体显性遗传性白内障家系致病基因的排除性定位

目的对常染色体显性遗传先天性白内障家系进行致病基因的定位研究。方法对4代11例家系成员（6例患者）进行眼部和全身检查,采集静脉血,提取基因组DNA,选取已报道的与遗传性白内障相关位点附近的微卫星标记,PCR扩增后进行基因型分析,用连锁分析进行排除;没有排除的位点,基因外显子测序。结果 35例家系成员中,追溯调查共有10例患者,其中第1代1例,第2代2例,第3代5例,第4代2例。该家系患者表型为完全性白内障;绝大多数位点,患者没有共享基因型;微卫星标记与致病基因间的2点连锁Lod值〈-2,证实这些位点与该家系的致病基因不连锁;有3个多态性标记（D10S1239、D22S286、D22S926）0〈Lod值≤0.6,Lod值虽然不是〈-2,但在家系患者中没有共享等位基因;测序未发现外显子有突变。结论此家系的致病基因不是已报道位点的致病基因,其致病基因有待进一步研究。     

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.     

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.     

A nonsense mutation in the glucosaminyl (N-acetyl) transferase 2 gene (GCNT2): association with autosomal recessive congenital cataracts

PURPOSE: To identify the genetic defect associated with autosomal recessive congenital cataract in four Arab families from Israel. METHODS: Genotyping was performed using microsatellite markers spaced at approximately 10 cM intervals. Two-point lod scores were calculated using MLINK of the LINKAGE program package. Mutation analysis of the glucosaminyl (N-acetyl) transferase 2 gene (GCNT2) gene was performed by direct sequencing of PCR-amplified exons. RESULTS: The cataract locus was mapped to a 13.0-cM interval between D6S470 and D6S289 on Chr. 6p24. A maximum two-point lod score of 8.75 at theta = 0.019 was obtained with marker D6S470. Sequencing exons of the GCNT2 gene, mutations of which have been associated with cataracts and the i blood group phenotype, revealed in these families a homozygous G-->A substitution in base 58 of exon-2, resulting in the formation of premature stop codons W328X, W326X, and W328X, of the GCNT2A, -B, and -C isoforms, respectively. Subsequent blood typing of affected family members confirmed the possession of the rare adult i blood group phenotype. CONCLUSIONS: A nonsense mutation in the GCNT2 gene isoforms is associated with autosomal recessive congenital cataract in four distantly related Arab families from Israel. These findings provide further insight into the dual role of the I-branching GCNT2 gene in the lens and in reticulocytes.     

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.     

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.     

Evidence of genetic heterogeneity in autosomal recessive congenital fibrosis of the extraocular muscles

PURPOSE: Autosomal recessive congenital fibrosis of the extraocular muscles (CFEOM2) has been described in families from Saudi Arabia. Affected individuals have ptosis and exotropic ophthalmoplegia, and their disease has been mapped to chromosome 11q13. Here, we describe the phenotypic findings in a similarly affected Yemenite family and analyze the family for linkage to the CFEOM2 locus, as well as to the autosomal dominant CFEOM1 and CFEOM3 loci on chromosomes 12cen and 16q24, respectively. METHODS: The family was ascertained through two affected daughters. There are four unaffected siblings, and the parents are consanguineous. Each family member was examined, and linkage analysis was performed using markers from the CFEOM1, CFEOM2, and CFEOM3 loci. RESULTS: Both affected daughters have congenital bilateral ophthalmoplegia. The 15-month-old proband has restrictive exotropia. She fixates with either eye in abduction and with a compensatory head turn to the opposite side. Her 4-year-old sister has a small exotropia and severely limited eye movements. All other family members have normal ophthalmologic examinations. Genetic analysis excluded linkage of the family's disease to the CFEOM2 and CFEOM3 loci. A lod score of 2.0 (the maximum possible, given the family size and structure), was obtained at the CFEOM1 locus, and the alleles reduced to homozygosity in both affected daughters and none of the other children. CONCLUSIONS: These data establish that there is genetic heterogeneity in autosomal recessive CFEOM and suggest that this second recessive locus may be allelic to the autosomal dominant CFEOM1 locus at 12cen.     

Locus for autosomal recessive nonsyndromic persistent hyperplastic primary vitreous

PURPOSE: To map the disease locus in a six-generation, consanguineous Pakistani family affected by nonsyndromic autosomal recessive persistent hyperplastic primary vitreous (arPHPV). All affected individuals had peripheral anterior synechiae and corneal opacities with variable degrees of cataract and a retrolenticular white mass behind the lens. METHODS: Genomic DNA from family members was typed for alleles at more than 400 known polymorphic genetic markers, by polymerase chain reaction. Alleles were assigned to individuals, which allowed calculation of lod scores. RESULTS: A maximum two-point lod score of 4.07 was obtained with marker D10S1225 with no recombination. Two recombinations with marker D10S208 and D10S537 localized the disease within a region of approximately 30 centimorgans (cM). However, homozygosity across the region refined the arPHPV locus to 13 cM. CONCLUSIONS: Linkage analysis shows localization of nonsyndromic arPHPV to chromosome10q11-q21.     

常染色体显性遗传核性白内障合并小角膜的CRYAA基因突变研究

目的 研究一个4代常染色体显性遗传先天性核性白内障伴小角膜家系的致病基因.方法 实验研究.对12例家系成员(6例患者,6例非患者)进行眼部检查并采集静脉血,提取基因组DNA.在已知的与先天性白内障伴小角膜相关致病基因附近选择微卫星标记,进行聚合酶链反应扩增-变性聚丙烯酰胺凝胶电泳,并进行基因型分析和连锁分析.对连锁区域内候选基因的外显子、外显子和内含子交界区进行测序.限制性内切酶ApaL Ⅰ法在全部家系成员和正常人群中验证突变.结果 该家系患者表型为先天性核性白内障伴小角膜;在染色体21q22.3区域的D21S1885和D21S1890两个标记,家系患者均有共享基因型,并且两点连锁分析Lod值为2.11,提示该位点与家系致病基因连锁;对此区域内候选基因CRYAA测序发现cDNA序列第34位碱基存在C＞T杂合突变(c.34C＞T),导致其编码肽链第12位精氨酸变为半胱氨酸(p.R12C).ApaL Ⅰ酶切验证家系患者均携带c.34C＞T突变,家系中及对照正常个体均不携带此突变.结论 CRYAA的p.R12C突变可能是该先天性白内障伴小角膜家系发病的遗传基础.

Abstract：

Objective To identify the gene mutation in a four-generation Chinese family with autosomal dominant congenital cataract associated with microcornea. Methods Experimental research.Twelve members in this family (including six affected and six unaffected individuals) were enrolled into this study. They underwent full ophthalmological and clinical examinations to rule out any concomitant disorders.Blood samples were collected and genomic DNA was extracted. Microsatellite markers near the reported loci,which are associated with congenital cataract and microcornea were selected and amplified from DNA samples using polymerase chain reaction. Linkage analysis was performed. The exons and exon/intron junction of candidate gene in the related chromosome were sequenced. The product of the first exon was digested by ApaL Ⅰ restriction enzyme to certify the mutation. Results The phenotype studied in this family was nuclear cataract accompanied with microcornea. At markers D21S1885 and D21S1890 near the locus 21q22. 3, the affected members had the same allele, but the unaffected did not. The Lod scores were 2. 11in both markers, indicating that this locus were linked to the congenital cataract in this family. DNA sequencing of candidate gene CRYAA showed a heterozygous mutation c. 34C ＞ T in exon 1, which led to condon 12 in peptide chain encoding arginine substituted by cysteine. ApaL Ⅰ enzyme digestion certified that all of the affected members had the same mutation c. 34C ＞T, but the unaffected and normal individuals did not. Conclusion Mutation (p. R12C) of CRYAA is the genetic change that causes the occurrence of congenital cataract with microcornea in this family.     

A novel locus for autosomal dominant nuclear cataract mapped to chromosome 2p12 in a Pakistani family

PURPOSE: To map the disease locus in a four-generation, consanguineous Pakistani family affected by autosomal dominant congenital nuclear cataract (adNCat). All affected individuals had early onset of bilateral nuclear cataract. METHODS: Genomic DNA from family members was typed for alleles at more than 300 known polymorphic genetic markers by polymerase chain reaction. The lod scores were calculated by using two-point linkage analysis of the genotyping data. RESULTS: The maximum lod score, 4.05, was obtained for the marker D2S2333. Proximal and distal crossovers were observed with markers D2S286 and D2S1790, respectively. These crossovers define the critical disease locus to an interval of approximately 9 centimorgans (cM). CONCLUSIONS: Linkage analysis identified a novel locus for adNCat on chromosome 2p12 in a Pakistani family. A genome database analysis of the target interval is being undertaken to identify candidate gene(s) for the disease.     

*常染色体显性先天性缝合状白内障家系致病基因的定位

目的对我国一常染色体显性先天性缝合状白内障家系进行致病基因的定位。方法采集家系成员外周静脉血提取基因组DNA。选用美国Applied Biosystems公司提供的约400个遗传标记物进行基因扫描。数据经Linkage软件包进行连锁分析,初步确定致病基因所在染色体区域。在阳性区域内选取更高密度的荧光标记物进行精细扫描,用Cyrillic软件进行单体型分析。结果两点间连锁分析在D3S1279处获得最大对数优势记分（LOD）值Zmax=2．32（θmax=0．00）。通过精细扫描和单体型分析将致病基因定位于D3S1267和D3S1614之间约38．6厘摩（cM）区域内。结论先天性缝合状白内障家系的致病基因位于3号染色体3q21．1-q26．2约38．6cM区域内。（中华腥科杂志,2006,42：908—912）     

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.     

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.