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 analysis of PITX2 and FOXC1 in Rieger Syndrome patients from Brazil

PURPOSE: Axenfeld-Rieger syndrome is a genetically heterogeneous, autosomal dominant disorder that is characterized by anterior segment defects, glaucoma, and extraocular anomalies. This study examined the two genes known to cause Rieger syndrome, PITX2 and FOXC1, for mutations in five Brazilian families with Axenfeld-Rieger syndrome. METHODS: Five families with a total of 23 persons affected by Axenfeld-Rieger syndrome were recruited for this study. A sequencing-based mutation screen was undertaken for the PITX2 and FOXC1 genes. Linkage analysis was used to study one large family for which no mutations were detected in the PITX2 or FOXC1 genes. RESULTS: Two of the five families harbored mutations in the PITX2 gene, but none of the families had a detectable FOXC1 mutation. Haplotypic analysis of three Rieger syndrome regions in a large family with Axenfeld-Rieger syndrome excluded linkage to the 4q25 (PITX2), 6p25 (FOXC1), and 13q14 (RIEG2) regions. CONCLUSIONS: It appears that the PITX2 gene is responsible for a significant portion of Axenfeld-Rieger syndrome in the Brazilian population. Furthermore, there is also evidence for the presence of genetic heterogeneity of the disorder within the Brazilian population. Finally, a large family with Axenfeld-Rieger syndrome has been identified that does not appear to harbor any of the three known loci. Axenfeld-Rieger syndrome gene segregation in this family likely represents a novel locus.     

Recessive congenital total cataract with microcornea and heterozygote carrier signs caused by a novel missense CRYAA mutation (R54C)

PURPOSE: To determine the genetic basis for congenital total white cataract with microcornea in three affected siblings. DESIGN: Prospective interventional case series. METHODS: Clinical ophthalmic examination, venous blood sampling for linkage analyses, and diagnostic testing of identified candidate gene(s). RESULTS: Three siblings had congenital total white cataract with microcornea; the parents and seven other siblings were asymptomatic. Linkage analysis mapped the phenotype to Hsa 21q22.3, the region of the gene for the alpha-A component of alpha-crystallin (CRYAA), with a logarithm of odds (LOD) score of 2.5. Diagnostic CRYAA sequencing revealed a novel homozygous nonsense mutation (R54C) in the three affected individuals only. One other sibling and the two parents were heterozygotes; these individuals had punctuate lenticular opacities evident by careful slit-lamp biomicroscopy which were not present in the noncarriers, all of whom had unremarkable ophthalmic examinations. CONCLUSION: R54C is the second reported recessive CRYAA mutation associated with congenital cataract and the first with described morphology: punctuate lenticular opacities in carriers and congenital total white cataract with microcornea in homozygotes. The microcornea may have been caused by an inductive effect on the developing cornea from the abnormal lens and/or reduced CRYAA molecular chaperoning of the cornea.     

Novel single-base deletional mutation in major intrinsic protein (MIP) in autosomal dominant cataract

PURPOSE: To further elucidate the cataract phenotype, and identify the gene and mutation for autosomal dominant cataract (ADC) in an American family of European descent (ADC2) by sequencing the major intrinsic protein gene (MIP), a candidate based on linkage to chromosome 12q13. DESIGN: Observational case series and laboratory experimental study. METHODS: We examined two at-risk individuals in ADC2. We PCR-amplified and sequenced all four exons and all intron-exon boundaries of the MIP gene from genomic and cloned DNA in affected members to confirm one variant as the putative mutation. RESULTS: We found a novel single deletion of nucleotide (nt) 3223 (within codon 235) in exon four, causing a frameshift that alters 41 of 45 subsequent amino acids and creates a premature stop codon. CONCLUSIONS: We identified a novel single base pair deletion in the MIP gene and conclude that it is a pathogenic sequence alteration.     

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.     

Structural assessment of PITX2, FOXC1, CYP1B1, and GJA1 genes in patients with Axenfeld-Rieger syndrome with developmental glaucoma

PURPOSE: Axenfeld-Rieger (AR) is an autosomal dominant disorder with phenotypic heterogeneity characterized by anterior segment dysgenesis, facial bone defects, and redundant periumbilical skin. The PITX2 gene, on chromosome 4q25, and the FOXC1 gene, on chromosome 6p25, have been implicated in the different phenotypes of the syndrome through mutational events. Recently, the CYP1B1 gene was found to be associated with Peters' anomaly, and the gene associated with oculodentodigital dysplasia syndrome, which presents some similarities with AR, was identified (connexin 43--GJA1 gene). The purpose of this study was to evaluate PITX2, FOXC1, CYP1B1, and GJA1 gene mutations in Brazilian families with AR. METHODS: Eight unrelated patients affected by AR (all eight with glaucoma and three with systemic manifestations) and their families were ophthalmologically evaluated and their blood was collected for DNA extraction purposes. The coding regions of PITX2, FOXC1, CYP1B1, and GJA1 genes were completely evaluated through direct sequencing. RESULTS: The frequency of mutations in the FOXC1, GJA1, PITX2, and CYP1B1 genes in this study were 25%, 12.5%, 0% and 0%, respectively. In the FOXC1 gene, two GGC triplet insertions (GGC375ins and GGC447ins) defined as a polymorphism, and two new mutations--a deletion (718 to 719delCT) and a nonsense mutation (Trp152STOP)--were identified. One polymorphism (Ala253Val) was identified in the GJA1 gene in the same family presenting the Trp152STOP mutation in the FOXC1 gene. In this family harboring both structural alterations, two patients who carried the GJA1 (Ala253Val) and FOXC1 (Trp152STOP) mutations developed less severe glaucoma compared with family members presenting the FOXC1 (Trp152STOP) mutation alone. CONCLUSIONS: Two new structural alterations in the FOXC1 gene and a polymorphism in the GJA1 gene were first described in Brazilian patients with AR and developmental glaucoma. A polymorphism in the GJA1 gene (Ala253Val), for the first time identified in association with AR, raises the possibility of its participation as a modifier gene.     

Later retinal degeneration following childhood surgical aphakia in a family with recessive CRYAB mutation (p.R56W)

Purpose:?To describe later retinal degeneration following childhood cataract surgery without intraocular lens implantation in a consanguineous family with developmental cataract from homozygous p.R56W mutation in CRYAB, a gene that encodes a heat-shock protein (αB-crystallin) in both retina and the lens.

Methods:?Prospective ophthalmologic examination and venous blood sampling for diagnostic CRYAB sequencing in the 12 available family members (7 siblings and their 2 parents, the siblings’ maternal aunt and her son, and the siblings’ maternal grandmother).

Results:?Those who underwent childhood cataract surgery (2 siblings, their mother, their maternal aunt) or who had visually-insignificant lens opacities (2 siblings, their maternal grandmother) were homozygous for p.R56W CRYAB mutation. Among these 7 affected family members, clinically-obvious rod-cone degeneration was present only in the only 2 adults who were aphakic since childhood from cataract surgery.

Conclusions:?Recessive p.R56W CRYAB mutation shows variable expressivity for lens opacity. Decades of aphakia increases retinal light exposure and may be an environmental risk factor for significant retinal degeneration in patients homozygous for the mutation.     

*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）     

Characterization and prevalence of PITX2 microdeletions and mutations in Axenfeld-Rieger malformations

PURPOSE: Mutations of the homeodomain protein PITX2 produce Axenfeld-Rieger (AR) malformations of the anterior chamber, an autosomal dominant disorder accompanied by a 50% risk of glaucoma. Twenty-nine mutations of PITX2 have been described, with a mutational prevalence estimated between 10% and 60% in AR. In the current study, the possible role of altered PITX2 gene dosage in the etiology of AR was investigated. Gross gene deletions and duplications should alter PITX2 activity analogously to hypomorphic and hypermorphic mutations, respectively. METHODS: Sixty-four patients with AR, iridogoniodysgenesis (IGD), iris hypoplasia (IH), or anterior segment dysgenesis (ASD) were screened for PITX2 mutations by sequencing. PITX2 gene dosage was concurrently examined in these patients by real-time quantitative PCR. Microsatellite markers were used to map 4q25 microdeletions at a contig scale, as well as for haplotype analysis in an extended AR kindred. An additional 27 patients with other assorted ocular phenotypes were evaluated by similar methods, amounting to a total of 91 cases analyzed. RESULTS: Three novel mutations of PITX2 (4.7%) were identified among 64 patients with AR, IGD, IH, or ASD. Deletions of PITX2 were as frequent as mutations in our sample. Chromosome 4q25 microdeletions were physically mapped relative to several microsatellite markers in each patient. Cosegregation of AR and a PITX2 deletion was demonstrated in an extended kindred. CONCLUSIONS: Point mutations and gross deletions of PITX2 appear to produce an equivalent haploinsufficiency phenotype. Quantitative PCR is an efficient means of detecting causative PITX2 deletions in patients with AR and may increase the detection rate at this locus.     

先天性粉尘状白内障一家系基因突变定位

目的 探讨先天性粉尘状白内障一家系的基因突变定位.方法 回顾性研究.对一先天性白内障家系成员(共32人,其巾患者15人)散瞳后采用裂隙灯显微镜观察晶状体,并取外周血提取DNA样品.选取常染色体上微卫星标记物,通过聚合酶链反应(PCR)进行扩增后,进行基因扫描.利用GeneMapper软件进行PCR扩增产物片段大小和单体型分析.分别通过Linkage 5.1和GeneHunter软件进行两点法和多点法对数优势记分(LOD)值计算.对候选基因通过测序进行基因序列分析.结果 家系成员中的白内障患者晶状体环胎儿核可见散在的类似于蚁卵的短棒状混浊.在不同患者间以及同一患者的不同眼别存在晶状体混浊程度和形态的差异.两点法计算LOD值,在重组率(θ)为0时,微卫星位点D20S186、D230S163、D20S915、D20S152、D20S98、D20S904、D20S875、D20S112、D20S1140、D20S432均获得正值,其中在D20S904获得最大LOD值6.02.通过单体型构建,发现微卫星位点D20S163在Ⅳ7患者发生交换,而D20S912在Ⅱ3患者发生交换.基因序列分析未发现BFSP1、PLCB4基因突变.结论 该家系突变基因位于常染色体20p12.1-p11.23上微卫星位点D20S186和D20S912间5.47厘摩范围内.     

Identification of a CRYAB mutation associated with autosomal dominant posterior polar cataract in a Chinese family

PURPOSE: A four-generation Chinese family with 13 members affected with autosomal dominant congenital posterior polar cataract was studied. The purpose of this study was to identify the disease-causing gene in the family and to validate that mutations in CRYAB, the alphaB-crystallin gene, cause the congenital cataract. METHODS: Linkage analysis was performed with a panel of microsatellite markers flanking candidate genetic loci for cataracts, including 14 known autosomal dominant congenital cataract (ADCC) genes. For mutation analysis, the complete coding region and exon-intron boundaries of CRYAB were sequenced with DNA from the proband. Single-strand conformation polymorphism (SSCP) analysis for exon 1 of CRYAB was performed in all family members and 200 normal control subjects. RESULTS: The disease gene in the Chinese family was mapped to chromosome 11 in region q22-22.3 with a maximum lod score of 4.52. Direct DNA sequence of CRYAB revealed a heterozygous C-->T transition at nucleotide 58, resulting in a novel 58 C-->T (Pro20Ser) mutation. The Pro20Ser mutation cosegregated with all affected individuals and was not present in unaffected members in the family or in 200 normal control subjects. The mutation occurs at the evolutionarily conserved residue Pro20 in the N-terminal region of alphaB-crystallin. CONCLUSIONS: To date, only one CRYAB mutation has been associated with congenital isolated cataract. This study identified a second novel mutation in CRYAB in a large Chinese cataract family. Together, these results provide strong evidence that CRYAB is a pathogenic gene for congenital cataract.     

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)     

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.     

先天性后极性白内障超微结构分析及突变基因筛查

目的 探讨一先天性后极性白内障家系晶状体的超微结构改变,并初步筛查其致病基因.方法 收集一常染色体显性遗传性先天性后极性白内障家系资料,对家系成员行眼部检查;在透射电镜下观察晶状体细胞超微结构的改变;选择CRYAB、CRYBA1/A3、CRYBB2、GJA8、CHMP4B、PITX3和EPHA2这7个热点基因进行突变位点筛查.结果 根据家系图分析该家系为垂直遗传,符合单基因常染色体显性遗传特点.裂隙灯显微镜下检查示全部患者晶状体混浊形态完全相同.透射电镜下发现患者前囊面晶状体上皮细胞排列紧密,结构完整,未见特异性病理变化;前皮质晶状体纤维细胞排列紧密,细胞内密度均一一致,但后皮质晶状体纤维细胞内出现斑驳状中高密度异常颗粒沉着.热点基因筛查显示:7个候选基因的外显子及其邻近内含子序列与基因库对照未发现任何突变.结论 本研究将后极性白内障病变定位于后皮质晶状体纤维细胞,排除了前囊面晶状体上皮细胞及前皮质晶状体纤维细胞.此家系携带的遗传突变位点位于尚未见报道的与后极性白内障相关的致病基因上.     

Genetic linkage analyses and Cx50 mutation detection in a large multiplex Chinese family with hereditary nuclear cataract

Purpose: The aim of the study was to characterize the underlying mutation in a large multiplex Chinese family with hereditary nuclear cataract.

Methods: A 6-generation Chinese family having hereditary nuclear cataract was recruited and clinically verified. Blood DNA samples were obtained from 53 available family members. Linkage analyses were performed on the known candidate regions for hereditary cataract with 36 polymorphic microsatellite markers. To identify mutations related to cataract, a direct sequencing approach was applied to a candidate gene residing in our linkage locus.

Results: A linkage locus was identified with a maximum 2-point LOD score of 4.31 (recombination fraction?=?0) at marker D1S498 and a maximum multipoint LOD score of 5.7 between markers D1S2344 and D1S498 on chromosome 1q21.1, where the candidate gene Cx50 is located. Direct sequencing of Cx50 showed a 139 G to A transition occurred in all affected family members. This transitional mutation resulted in a replacement of aspartic acid by asparagine at residue 47 (D47N) and led to a loss-of-function of the protein.

Conclusions: The D47N mutation of Cx50 causes the hereditary nuclear cataract in this family in an autosomal dominant mode of inheritance with incomplete penetrance.     

A new autosomal dominant Peters’ anomaly phenotype expanding the anterior segment dysgenesis spectrum

Purpose: To test the association of genes involved in anterior segment development in a family with autosomal dominantly inherited Peters’ anomaly (PA) with a unique ocular phenotype. Methods: Six members of a five‐generation family with PA were extensively phenotyped and linkage analysis of candidate genes, namely, PAX6, PITX2, FOXC1, CYP1B1 and MAF, was performed. Results: The complete pedigree consisted of 38 members, 19 of whom were affected. The six probands examined had bilateral microcornea, corneal opacity, iridocorneal adhesions, nystagmus and strabismus, but cataract, keratolenticular adhesions, glaucoma and posterior embryotoxon were absent. PAX6 gene mutations had been previously excluded in one of the affected members. DNA markers for candidate genes CYP1B1 on 2p22, PITX2 on 4q25, PAX6 on 11p13, MAF on 16q23 and FOXC1 on 6p25 were genotyped. Highly negative lod scores were obtained for all markers. Conclusions: The exclusion of these genes as likely candidates supports the hypothesis that the ocular phenotype associated with PA segregating in this family is a distinct, new, autosomal dominant entity in the anterior segment dysgenesis spectrum.