A progressive autosomal recessive cataract locus maps to chromosome 9q13-q22

Inherited cataracts: Genetic mechanisms and pathways new and old

Cataract(s) is the clinical equivalent of lens opacity and is caused by light scattering either by high molecular weight protein aggregates in lens cells or disruption of the lens microarchitecture itself. Genetic mutations underlying inherited cataract can provide insight into the biological processes and pathways critical for lens homeostasis and transparency, classically including the lens crystallins, connexins, membrane proteins or components, and intermediate filament proteins. More recently, cataract genes have been expanded to include newly identified biological processes such as chaperone or protein degradation components, transcription or growth factors, channels active in the lens circulation, and collagen and extracellular matrix components. Cataracts can be classified by age, and in general congenital cataracts are caused by severe mutations resulting in major damage to lens proteins, while age related cataracts are associated with variants that merely destabilize proteins thereby increasing susceptibility to environmental insults over time. Thus there might be separate pathways to opacity for congenital and age-related cataracts whereby congenital cataracts induce the unfolded protein response (UPR) and apoptosis to destroy the lens microarchitecture, while in age related cataract high molecular weight (HMW) aggregates formed by denatured crystallins bound by α-crystallin result in light scattering without severe damage to the lens microarchitecture.

Autosomal recessive congenital cataracts linked to HSF4 in a consanguineous Pakistani family

PURPOSE

To investigate the genetic basis of autosomal recessive congenital cataracts (arCC) in a large consanguineous Pakistani family.

METHODS

All participating members of family, PKCC074 underwent an ophthalmic examination. Slit-lamp photographs were ascertained for affected individuals that have not been operated for the removal of the cataractous lens. A small aliquot of the blood sample was collected from all participating individuals and genomic DNAs were extracted. A genome-wide scan was performed with polymorphic short tandem repeat (STR) markers and the logarithm of odds (LOD) scores were calculated. All coding exons and exon-intron boundaries of HSF4 were sequenced and expression of Hsf4 in mouse ocular lens was investigated. The C-terminal FLAG-tagged wild-type and mutant HSF4b constructs were prepared to examine the nuclear localization pattern of the mutant protein.

RESULTS

The ophthalmological examinations suggested that nuclear cataracts are present in affected individuals. Genome-wide linkage analyses localized the critical interval to a 10.95 cM (14.17 Mb) interval on chromosome 16q with a maximum two-point LOD score of 4.51 at θ = 0. Sanger sequencing identified a novel missense mutation: c.433G>C (p.Ala145Pro) that segregated with the disease phenotype in the family and was not present in ethnically matched controls. Real-time PCR analysis identified the expression of HSF4 in mouse lens as early as embryonic day 15 with a steady level of expression thereafter. The immunofluorescence tracking confirmed that both wild-type and mutant HSF4 (p.Ala145Pro) proteins localized to the nucleus.

CONCLUSION

Here, we report a novel missense mutation in HSF4 associated with arCC in a familial case of Pakistani descent.

Effects of chromosome 9 inversion on IVF/ICSI: A 7-year retrospective cohort study

Background

This study focused on the outcomes of patients with pericentric inversion of chromosome 9 who underwent IVF/ICSI and fresh day 2 or day 3 embryo transfer and the possible impacts of carrier gender and chromosome karyotype on pregnancy outcomes.

Methods

A total of 214 couples (107 couples with one pericentric inversion of chromosome 9 in one partner [Group 1], 107 couples with normal karyotypes [Group 2]) underwent their first IVF/ICSI treatment and were included in this study. Oocyte number, normal fertilization rates, abnormal fertilization rates, cleavage rates, embryo utilization rates, fresh embryo transfer rates, clinical pregnancy rates (CPR), implantation rates, miscarriage rates, and live birth rates per embryo transfer (LBR) were compared between groups.

Results

Group 1 did not show any disadvantage when compared with Group 2. The CPR and LBR were similar between all groups. The female carrier group had a higher normal fertilization rate and higher utilization rate than the male carrier group. Cases with inv(9)(p12;q13) had a lower utilization rate but a higher implantation rate than the remaining karyotypes.

Conclusion

In the first IVF or ICSI cycle, couples with one pericentric inversion of chromosome 9 in one partner had satisfactory outcomes. The subgroup analysis showed a tendency of better prognosis for the female carrier and inv(9)(p12;q13) type.

This is a retrospective cohort study during 7 years period. In the first IVF or ICSI cycle, couples with one pericentric inversion of chromosome 9 in one partner had satisfactory outcomes. The subgroup analysis showed a tendency of better prognosis for the female carrier and inv(9)(p12;q13) type.

Fine mapping of chromosome 9 locus associated with congenital cataract

PURPOSE

The purpose of this study was to study the molecular basis of inherited autosomal recessive cataracts in Pakistan population and to identify the molecular defect segregating with the disease phenotype.

METHODS

Families having two or more affected individuals were identified through hospital, blood samples were collected and DNA was extracted. We employed the traditional strategy of linkage analysis using M13-labeled primers to map the already known genes for autosomal recessive cataract. Statistically, the data were evaluated through LOD score.

RESULTS

Ten families affected with autosomal receive congenital cataract were enrolled for this study. Overall, three families were linked to reported loci for autosomal recessive congenital cataract. Out of these, one family Bl05 was linked to a cataract locus at 9q13. Fine mapping of the chromosome 9 locus considerably delimited the previously reported linkage interval from 13.99 to 7.99 cM in this study.

CONCLUSION

Our results reduced the linkage interval of previously reported cataract locus on chromosome 9, thus considerably reducing the number of candidate genes.

Inherited Congenital Cataract: A Guide to Suspect the Genetic Etiology in the Cataract Genesis

Cataracts are the principal cause of treatable blindness worldwide. Inherited congenital cataract (CC) shows all types of inheritance patterns in a syndromic and nonsyndromic form. There are more than 100 genes associated with cataract with a predominance of autosomal dominant inheritance. A cataract is defined as an opacity of the lens producing a variation of the refractive index of the lens. This variation derives from modifications in the lens structure resulting in light scattering, frequently a consequence of a significant concentration of high-molecular-weight protein aggregates. The aim of this review is to introduce a guide to identify the gene involved in inherited CC. Due to the manifold clinical and genetic heterogeneity, we discarded the cataract phenotype as a cardinal sign; a 4-group classification with the genes implicated in inherited CC is proposed. We consider that this classification will assist in identifying the probable gene involved in inherited CC.

Cataracts in the Norwegian Buhund-current prevalence and characteristics

OBJECTIVE

To evaluate prevalence and characteristics of cataracts in the Norwegian Buhund breed 20 years after high reported prevalence of especially pulverulent nuclear cataracts (PNCs).

ANIMALS STUDIED

Two hundred and fifty Norwegian Buhund dogs in Norway, Sweden, and Denmark (117 males and 133 females) with previously unknown eye health status were included. Forty-five dogs had multiple examinations (two to six times over a 6-year period). Median age was 4.4 years [0.2-15.2] at first examination and 5.3 years [0.2-15.2] at last examination.

PROCEDURES

All dogs underwent regular screening for inherited eye diseases.

RESULTS

At the last observation of each dog, 52.4% were affected by PNC, categorized as minimal (33 of 250 dogs; 13.2%), mild (31 dogs; 12.4%), moderate (38 dogs; 15.2%), or pronounced (29 dogs; 11.6%). Moderate or pronounced changes were only seen in older dogs, and progressive changes were identified in some of the re-examined dogs. Some dogs, free of lenticular changes at early examinations, were affected by PNC at re-examinations. The odds for finding PNC increased with dog's age up to approximately 8 years. Presumably inherited cataracts other than PNC were found in 53 dogs (21.2%) with cortical (17.6%) and posterior polar (6.4%) locations as the most common ones.

CONCLUSIONS

The high prevalence of PNC in the breed reported 20 years ago persists. PNCs are not always visible in young dogs, and the rate of progression varies. The prevalence of other types of cataract is also high, but cataracts rarely cause loss of vision in this breed.

Deletion at the GCNT2 Locus Causes Autosomal Recessive Congenital Cataracts

PURPOSE

The aim of this study is to identify the molecular basis of autosomal recessive congenital cataracts (arCC) in a large consanguineous pedigree.

METHODS

All participating individuals underwent a detailed ophthalmic examination. Each patient's medical history, particularly of cataracts and other ocular abnormalities, was compiled from available medical records and interviews with family elders. Blood samples were donated by all participating family members and used to extract genomic DNA. Genetic analysis was performed to rule out linkage to known arCC loci and genes. Whole-exome sequencing libraries were prepared and paired-end sequenced. A large deletion was found that segregated with arCC in the family, and chromosome walking was conducted to estimate the proximal and distal boundaries of the deletion mutation.

RESULTS

Exclusion and linkage analysis suggested linkage to a region of chromosome 6p24 harboring GCNT2 (glucosaminyl (N-acetyl) transferase 2) with a two-point logarithm of odds score of 5.78. PCR amplifications of the coding exons of GCNT2 failed in individuals with arCC, and whole-exome data analysis revealed a large deletion on chromosome 6p in the region harboring GCNT2. Chromosomal walking using multiple primer pairs delineated the extent of the deletion to approximately 190 kb. Interestingly, a failure to amplify a junctional fragment of the deletion break strongly suggests an insertion in addition to the large deletion.

CONCLUSION

Here, we report a novel insertion/deletion mutation at the GCNT2 locus that is responsible for congenital cataracts in a large consanguineous family.

A Novel CRYBB2 Stopgain Mutation Causing Congenital Autosomal Dominant Cataract in a Chinese Family

Congenital cataract is the most common cause of the visual disability and blindness in childhood. This study aimed to identify gene mutations responsible for autosomal dominant congenital cataract (ADCC) in a Chinese family using next-generation sequencing technology. This family included eight unaffected and five affected individuals. After complete ophthalmic examinations, the blood samples of the proband and two available family members were collected. Then the whole exome sequencing was performed on the proband and Sanger sequencing was applied to validate the causal mutation in the two family members and control samples. After the whole exome sequencing data were filtered through a series of existing variation databases, a heterozygous mutation c.499T<G (p.E167X) in CRYBB2 gene was found. And the results showed that the mutation cosegregated with the disease phenotype in the family and was absolutely absent in 1000 ethnicity-matched control samples. Thus, the heterozygous mutation c.499T<G (p.E167X) in CRYBB2 was the causal mutation responsible for this ADCC family. In conclusion, our findings revealed a novel stopgain mutation c.499T<G (p.E167X) in the exon 6 of CRYBB2 which expanded the mutation spectrum of CRYBB2 in Chinese congenital cataract population and illustrated the important role of CRYBB2 in the genetics research of congenital cataract.

Mutation in LIM2 Is Responsible for Autosomal Recessive Congenital Cataracts

Purpose

To identify the molecular basis of non-syndromic autosomal recessive congenital cataracts (arCC) in a consanguineous family.

Methods

All family members participating in the study received a comprehensive ophthalmic examination to determine their ocular phenotype and contributed a blood sample, from which genomic DNA was extracted. Available medical records and interviews with the family were used to compile the medical history of the family. The symptomatic history of the individuals exhibiting cataracts was confirmed by slit-lamp biomicroscopy. A genome-wide linkage analysis was performed to localize the disease interval. The candidate gene, LIM2 (lens intrinsic membrane protein 2), was sequenced bi-directionally to identify the disease-causing mutation. The physical changes caused by the mutation were analyzed in silico through homology modeling, mutation and bioinformatic algorithms, and evolutionary conservation databases. The physiological importance of LIM2 to ocular development was assessed in vivo by real-time expression analysis of Lim2 in a mouse model.

Results

Ophthalmic examination confirmed the diagnosis of nuclear cataracts in the affected members of the family; the inheritance pattern and cataract development in early infancy indicated arCC. Genome-wide linkage analysis localized the critical interval to chromosome 19q with a two-point logarithm of odds (LOD) score of 3.25. Bidirectional sequencing identified a novel missense mutation, c.233G>A (p.G78D) in LIM2. This mutation segregated with the disease phenotype and was absent in 192 ethnically matched control chromosomes. In silico analysis predicted lower hydropathicity and hydrophobicity but higher polarity of the mutant LIM2-encoded protein (MP19) compared to the wild-type. Moreover, these analyses predicted that the mutation would disrupt the secondary structure of a transmembrane domain of MP19. The expression of Lim2, which was detected in the mouse lens as early as embryonic day 15 (E15) increased after birth to a level that was sustained through the postnatal time points.

Conclusion

A novel missense mutation in LIM2 is responsible for autosomal recessive congenital cataracts.

A Common Ancestral Mutation in CRYBB3 Identified in Multiple Consanguineous Families with Congenital Cataracts

PURPOSE

This study was performed to investigate the genetic determinants of autosomal recessive congenital cataracts in large consanguineous families.

METHODS

Affected individuals underwent a detailed ophthalmological examination and slit-lamp photographs of the cataractous lenses were obtained. An aliquot of blood was collected from all participating family members and genomic DNA was extracted from white blood cells. Initially, a genome-wide scan was performed with genomic DNAs of family PKCC025 followed by exclusion analysis of our familial cohort of congenital cataracts. Protein-coding exons of CRYBB1, CRYBB2, CRYBB3, and CRYBA4 were sequenced bidirectionally. A haplotype was constructed with SNPs flanking the causal mutation for affected individuals in all four families, while the probability that the four familial cases have a common founder was estimated using EM and CHM-based algorithms. The expression of Crybb3 in the developing murine lens was investigated using TaqMan assays.

RESULTS

The clinical and ophthalmological examinations suggested that all affected individuals had nuclear cataracts. Genome-wide linkage analysis localized the causal phenotype in family PKCC025 to chromosome 22q with statistically significant two-point logarithm of odds (LOD) scores. Subsequently, we localized three additional families, PKCC063, PKCC131, and PKCC168 to chromosome 22q. Bidirectional Sanger sequencing identified a missense variation: c.493G>C (p.Gly165Arg) in CRYBB3 that segregated with the disease phenotype in all four familial cases. This variation was not found in ethnically matched control chromosomes, the NHLBI exome variant server, or the 1000 Genomes or dbSNP databases. Interestingly, all four families harbor a unique disease haplotype that strongly suggests a common founder of the causal mutation (p<1.64E-10). We observed expression of Crybb3 in the mouse lens as early as embryonic day 15 (E15), and expression remained relatively steady throughout development.

CONCLUSION

Here, we report a common ancestral mutation in CRYBB3 associated with autosomal recessive congenital cataracts identified in four familial cases of Pakistani origin.

Missense Mutations in CRYAB Are Liable for Recessive Congenital Cataracts

PURPOSE

This study was initiated to identify causal mutations responsible for autosomal recessive congenital cataracts in consanguineous familial cases.

METHODS

Affected individuals underwent a detailed ophthalmological and clinical examination, and slit-lamp photographs were ascertained for affected individuals who have not yet been operated for the removal of the cataractous lens. Blood samples were obtained, and genomic DNA was extracted from white blood cells. A genome-wide scan was completed with short tandem repeat (STR) markers, and the logarithm of odds (LOD) scores were calculated. Protein coding exons of CRYAB were sequenced, bi-directionally. Evolutionary conservation was investigated by aligning CRYAB orthologues, and the expression of Cryab in embryonic and postnatal mice lens was investigated with TaqMan probe.

RESULTS

The clinical and ophthalmological examinations suggested that all affected individuals had nuclear cataracts. Genome-wide linkage analysis suggested a potential region on chromosome 11q23 harboring CRYAB. DNA sequencing identified a missense variation: c.34C>T (p.R12C) in CRYAB that segregated with the disease phenotype in the family. Subsequent interrogation of our entire cohort of familial cases identified a second familial case localized to chromosome 11q23 harboring a c.31C>T (p.R11C) mutation. In silico analyses suggested that the mutations identified in familial cases, p.R11C and p.R12C will not be tolerated by the three-dimensional structure of CRYAB. Real-time PCR analysis identified the expression of Cryab in mouse lens as early as embryonic day 15 (E15) that increased significantly until postnatal day 6 (P6) with steady level of expression thereafter.

CONCLUSION

Here, we report two novel missense mutations, p.R11C and p.R12C, in CRYAB associated with autosomal recessive congenital nuclear cataracts.

Mutation of the melastatin-related cation channel, TRPM3, underlies inherited cataract and glaucoma

Inherited forms of cataract are a clinically important and genetically heterogeneous cause of visual impairment that usually present at an early age with or without systemic and/or other ocular abnormalities. Here we have identified a new locus for inherited cataract and high-tension glaucoma with variable anterior segment defects, and characterized an underlying mutation in the gene coding for transient receptor potential cation channel, subfamily M, member-3 (TRPM3, melastatin-2). Genome-wide linkage analysis mapped the ocular disease locus to the pericentric region of human chromosome 9. Whole exome and custom-target next-generation sequencing detected a heterozygous A-to-G transition in exon-3 of TRPM3 that co-segregated with disease. As a consequence of alternative splicing this missense mutation was predicted to result in the substitution of isoleucine-to-methionine at codon 65 (c.195A>G; p.I65 M) of TRPM3 transcript variant 9, and at codon 8 (c.24A>G; p.I8 M) of a novel TRPM3 transcript variant expressed in human lens. In both transcript variants the I-to-M substitution was predicted in silico to exert damaging effects on protein function. Furthermore, transient expression studies of a recombinant TRPM3-GFP reporter product predicted that the I-to-M substitution introduced an alternative translation start-site located 89 codons upstream from the native initiator methionine found in eight other TRPM3 transcript variants (1-8). Collectively, these studies have provided the first evidence that TRPM3 is associated with inherited ocular disease in humans, and further provide support for the important role of this cation channel in normal eye development.

Genetic heterogeneity for recessively inherited congenital cataract microcornea with corneal opacity

PURPOSE

To investigate whether three consanguineous families from the Punjab province of Pakistan, with affected members with recessively inherited congenital cataract microcornea with corneal opacity, are genetically homogeneous.

METHODS

An ophthalmic examination was performed on each family member to establish the diagnosis. The two largest families were analyzed by homozygosity mapping using SNP arrays. Linkage was confirmed using polymorphic microsatellite markers, and logarithm of odds (LOD) scores were calculated. Candidate genes were prioritized using the ENDEAVOUR program.

RESULTS

Autosomal recessive congenital cataract-microcornea with corneal opacity mapped to chromosome 10cen for family MEP57 and to either chromosomes 2ptel or 20p for family MEP60. For MEP57, the refined interval was 36.8 Mb flanked by D10S1208 (35.3 Mb) and D10S676 (72.1 Mb). For MEP60, the interval containing the mutation was either 6.7 Mb from the telomere of chromosome 2 to marker D2S281 or 3.8 Mb flanked by D20S906 (1.5 Mb) and D20S835 (5.3 Mb). Maximum multipoint LOD scores of 3.09, 1.94, and 3.09 were calculated at D10S567, D2S281, and D20S473 for families MEP57 and MEP60. Linkage to these loci was excluded for family MEP68. SLC4A11 was excluded as a candidate gene for the observed phenotype in MEP60.

CONCLUSIONS

The authors have identified two new loci, one on chromosome 10cen and the other on 2ptel or 20p, that are associated with recessively inherited congenital cataract-microcornea with corneal opacity. This phenotype is genetically heterogeneous in the Pakistani population. Further genetic studies of this kind, combined with a detailed phenotypic description, will contribute to more precise classification criteria for anterior segment disease.

Mapping of a novel locus associated with autosomal recessive congenital cataract to chromosome 8p

PURPOSE

To identify the disease locus for autosomal recessive congenital cataracts in a consanguineous Pakistani family.

METHODS

All affected individuals underwent a detailed ophthalmologic examination. Blood samples were collected and genomic DNA was extracted. A genome-wide scan was completed with fluorescently-labeled microsatellite markers on genomic DNA from affected and unaffected family members. Logarithms of odds (LOD) scores were calculated under a fully penetrant autosomal recessive model of inheritance.

RESULTS

Ophthalmic examination suggested that affected individuals have bilateral cataracts. Linkage analysis localized the critical interval to chromosome 8p with LOD scores of 3.19, and 3.08 at θ=0, obtained with markers D8S549 and D8S550, respectively. Haplotype analyses refined the critical interval to 37.92 cM (16.28 Mb) region, flanked by markers, D8S277 proximally and D8S1734 distally.

CONCLUSIONS

Here, we report a new locus for autosomal recessive congenital cataract mapped to chromosome 8p in a consanguineous Pakistani family.

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.

Mapping of a new locus associated with autosomal recessive congenital cataract to chromosome 3q

PURPOSE

To localize the disease interval for autosomal recessive congenital cataracts in a consanguineous Pakistani family.

METHODS

All affected individuals underwent detailed ophthalmologic examination. Blood samples were collected and genomic DNA was extracted. A genome-wide scan was performed with fluorescently-labeled microsatellite markers on genomic DNA from affected and unaffected family members and logarithm of odds (LOD) scores were calculated.

RESULTS

Clinical records and ophthalmological examinations suggested that affected individuals have bilateral congenital cataracts. Genome-wide linkage analysis localized the critical interval to chromosome 3q with a maximum LOD score of 3.87 at θ=0; with marker D3S3609. Haplotype analyses refined the critical interval to a 23.39 cM (18.01 Mb) interval on chromosome 3q, flanked by D3S1614 proximally and D3S1262, distally.

CONCLUSIONS

Here, we report a new locus for autosomal recessive congenital cataract localized to chromosome 3q in a consanguineous Pakistani family.

Cat-Map: putting cataract on the map

Lens opacities, or cataract(s), may be inherited as a classic Mendelian disorder usually with early-onset or, more commonly, acquired with age as a multi-factorial or complex trait. Many genetic forms of cataract have been described in mice and other animal models. Considerable progress has been made in mapping and identifying the genes and mutations responsible for inherited forms of cataract, and genetic determinants of age-related cataract are beginning to be discovered. To provide a convenient and accurate summary of current information focused on the increasing genetic complexity of Mendelian and age-related cataract we have created an online chromosome map and reference database for cataract in humans and mice (Cat-Map).

Coexistence of mal de Meleda and congenital cataract in a consanguineous Tunisian family: two case reports

Introduction

Mal de Meleda is a rare form of palmoplantar keratoderma, with autosomal recessive transmission. It is characterized by diffuse erythema and hyperkeratosis of the palms and soles. Recently, mutations in the ARS (component B) gene (ARS, MIM: 606119) on chromosome 8q24.3 have been identified in families with this disorder. Congenital cataract is a visual disease that may interfere with sharp imaging of the retina. Mutations in the heat-shock transcription factor 4 gene (HSF4; MIM: 602438) may result in both autosomal dominant and autosomal recessive congenital cataracts.

Case presentation

A Tunisian family with two female siblings aged 45 and 30 years, presented with a clinical association of mal de Meleda and congenital cataract. The two patients exhibited diffuse palmoplantar keratodermas. One of them presented with a total posterior subcapsular cataract and had a best corrected visual acuity at 1/20 in the left eye and with the right eye was only able to count fingers at a distance of one foot. The other woman had a slight posterior subcapsular lenticular opacity and her best corrected visual acuity was 8/10 in the right eye and with her left eye she was only able to count fingers at a distance of one foot. A mutational analysis of their ARS gene revealed the presence of the homozygous missense mutation C99Y and two single nucleotide polymorphisms (-55G>C and -60G>C). The splice mutation (c.1327+4A-G) within intron 12 of the HSF4 gene, which has been previously described in Tunisian families with congenital cataract, was not found in the two probands within this family.

Conclusion

To the best of our knowledge, such original clinical association has not been reported previously. The association of these two autosomal recessive diseases might have occurred in this family due to a high degree of inbreeding. The C99Y mutation may be specific to the Tunisian population as it has been exclusively reported so far in only three Tunisian families with mal de Meleda.

Autosomal recessive congenital cataract in consanguineous Pakistani families is associated with mutations in GALK1

PURPOSE

To identify the pathogenic mutations responsible for autosomal recessive congenital cataracts in consanguineous Pakistani families.

METHODS

All affected individuals underwent detailed ophthalmologic and medical examination. Blood samples were collected and genomic DNA was extracted. A genome-wide scan was performed with polymorphic microsatellite markers on genomic DNA from affected and unaffected family members and logarithm of odds (LOD) scores were calculated. All coding exons of galactokinase (GALK1) were sequenced to identify pathogenic lesions.

RESULTS

Clinical records and ophthalmological examinations suggested that affected individuals have nuclear cataracts. Linkage analysis localized the critical interval to chromosome 17q with a maximum LOD score of 5.54 at theta=0, with D17S785 in family PKCC030. Sequencing of GALK1, a gene present in the critical interval, identified a single base pair deletion: c.410delG, which results in a frame shift leading to a premature termination of GALK1: p.G137fsX27. Additionally, we identified a missense mutation: c.416T>C, in family PKCC055 that results in substitution of a leucine residue at position 139 with a proline residue: p.L139P, and is predicted to be deleterious to the native GALK1 structure.

CONCLUSIONS

Here, we report pathogenic mutations in GALK1 that are responsible for autosomal recessive congenital cataracts in consanguineous Pakistani families.

Autosomal recessive congenital cataract linked to EPHA2 in a consanguineous Pakistani family

PURPOSE

To investigate the genetic basis of autosomal recessive congenital cataracts in a consanguineous Pakistani family.

METHODS

All affected individuals underwent a detailed ophthalmological and clinical examination. Blood samples were collected and genomic DNAs were extracted. A genome-wide scan was performed with polymorphic microsatellite markers. Logarithm of odds (LOD) scores were calculated, and Eph-receptor type-A2 (EPHA2), residing in the critical interval, was sequenced bidirectionally.

RESULTS

The clinical and ophthalmological examinations suggested that all affected individuals have nuclear cataracts. Genome-wide linkage analyses localized the critical interval to a 20.78 cM (15.08 Mb) interval on chromosome 1p, with a maximum two-point LOD score of 5.21 at theta=0. Sequencing of EPHA2 residing in the critical interval identified a missense mutation: c.2353G>A, which results in an alanine to threonine substitution (p.A785T).

CONCLUSIONS

Here, we report for the first time a missense mutation in EPHA2 associated with autosomal recessive congenital cataracts.

A new locus for autosomal recessive congenital cataract identified in a Pakistani family

PURPOSE

To identify the disease locus for autosomal recessive congenital cataract in a consanguineous Pakistani family.

METHODS

All affected individuals underwent detailed ophthalmologic and medical examination. Blood samples were collected and DNA was extracted. A genome-wide scan was performed with polymorphic microsatellite markers on genomic DNA from affected and unaffected family members, and logarithm of odds (LOD) scores were calculated.

RESULTS

The clinical records and ophthalmological examinations suggested that all affected individuals have nuclear cataracts. Maximum LOD scores of 5.01, 4.38, and 4.17 at theta=0 were obtained with markers D7630, D7S657, and D7S515, respectively. Fine mapping refined the critical interval and suggested that markers in a 27.78 cM (27.96 Mb) interval are flanked by markers D7S660 and D7S799, which co-segregate with the disease phenotype in family PKCC108.

CONCLUSIONS

We have identified a new locus for autosomal recessive congenital cataract, localized to chromosome 7q21.11-q31.1 in a consanguineous Pakistani family.

Initiation codon mutation in betaB1-crystallin (CRYBB1) associated with autosomal recessive nuclear pulverulent cataract

PURPOSE

To identify the molecular basis for autosomal recessively inherited congenital non-syndromic pulverulent cataracts in a consanguineous family with four affected children.

METHODS

An autozygosity mapping strategy using high density SNP microarrays and microsatellite markers was employed to detect regions of homozygosity. Subsequently good candidate genes were screened for mutations by direct sequencing.

RESULTS

The SNP microarray data demonstrated a 24.96 Mb region of homozygosity at 22q11.21-22q13.2 which was confirmed by microsatellite marker analysis. The candidate target region contained the beta-crystallin gene cluster and direct sequencing in affected family members revealed a novel mutation in CRYBB1 (c.2T>A; p.Met1Lys).

CONCLUSIONS

To our knowledge this is the first case of an initiation codon mutation in a human crystallin gene, and only the second report of a CRYBB1 mutation associated with autosomal recessive congenital cataracts. In addition, although a number of genetic causes of autosomal dominant pulverulent cataracts have been identified (including CRYBB1) this is the first gene to have been implicated in autosomal recessive nuclear pulverulent cataract.

Cystatin C, other markers of kidney disease, and incidence of age-related cataract

OBJECTIVE

To investigate the 15-year incidence of 3 specific types of age-related cataract as related to cystatin C and other measures of kidney function.

METHODS

Examinations of a population-based cohort (n = 4926) occurred at 5-year intervals for 15 years. Assessment of medical history, examination, and photographs of the lens after pupil dilation were performed at each examination. Protocols for photography and grading were used. Laboratory measures were from specimens collected at baseline.

RESULTS

In multivariable analyses, a 1-SD increase in the logarithm of cystatin C was associated with 15-year incidence of cortical (odds ratio [OR], 1.24; 95% confidence interval [CI], 1.09-1.41) and posterior subcapsular (OR, 1.24; 95% CI, 1.02-1.50) cataracts. One SD increase in the logarithm of blood urea nitrogen and creatinine were associated with 15-year incidence of posterior subcapsular cataract (OR, 1.22; 95% CI, 1.04-1.42 and OR, 1.26; 95% CI, 1.03-1.54, respectively).

CONCLUSION

Increased levels of cystatin C are associated with increased risk of specific types of age-related cataract. Whether the associations are due to the metabolic changes associated with decreased renal function, common genes, or both awaits further research.

A novel HSF4 gene mutation (p.R405X) causing autosomal recessive congenital cataracts in a large consanguineous family from Pakistan

Background

Hereditary cataracts are most frequently inherited as autosomal dominant traits, but can also be inherited in an autosomal recessive or X-linked fashion. To date, 12 loci for autosomal recessive cataracts have been mapped including a locus on chromosome 16q22 containing the disease-causing gene HSF4 (Genbank accession number NM_001040667). Here, we describe a family from Pakistan with the first nonsense mutation in HSF4 thus expanding the mutational spectrum of this heat shock transcription factor gene.

Methods

A large consanguineous Pakistani family with autosomal recessive cataracts was collected from Quetta. Genetic linkage analysis was performed for the common known autosomal recessive cataracts loci and linkage to a locus containing HSF4 (OMIM 602438) was found. All exons and adjacent splice sites of the heat shock transcription factor 4 gene (HSF4) were sequenced. A mutation-specific restriction enzyme digest (HphI) was performed for all family members and unrelated controls.

Results

The disease phenotype perfectly co-segregated with markers flanking the known cataract gene HSF4, whereas other autosomal recessive loci were excluded. A maximum two-point LOD score with a Zmax = 5.6 at θ = 0 was obtained for D16S421. Direct sequencing of HSF4 revealed the nucleotide exchange c.1213C > T in this family predicting an arginine to stop codon exchange (p.R405X).

Conclusion

We identified the first nonsense mutation (p.R405X) in exon 11 of HSF4 in a large consanguineous Pakistani family with autosomal recessive cataract.

A novel mutation in CRYBB2 responsible for inherited coronary cataract

PURPOSE

To study the molecular pathogenesis of a Chinese family with coronary form of cataract.

METHODS

One Chinese three-generation family with inherited coronary cataract phenotype was recruited. Five affected and seven unaffected family members attended our study. Genome-wide linkage analysis was applied to map the disease loci, and two candidate genes from a locus on chromosome 1 and a locus on chromosome 22 were sequenced for mutation identification. Software at the Expasy proteomics server was utilized to predict the mutation effect on proteins.

RESULTS

Whole genome linkage analysis indicated some regions on chromosome 1, 10, and 22, with LOD score values greater than 1. Within these loci, the GJA8 and CRYBB2 genes, located in the two loci with the highest LOD score of 1.51 on chromosomes 1 and 22, respectively, were sequenced. A novel mutation c.92C>G in exon 2 of CRYBB2 causing S31W was identified in all five patients. It was not found in 95 unrelated controls. This missense sequence alteration likely enhanced the local solubility. Around the mutation site, a lipocalin signature motif was predicted by ScanProsite.

CONCLUSIONS

A novel disease-causing mutation S31W in CRYBB2 was identified in a Chinese cataract family. It is the first reported mutation for coronary cataract. Functional characterization should be carried out to evaluate the biological effects of this mutant.

Congenital cataracts and their molecular genetics

Cataract can be defined as any opacity of the crystalline lens. Congenital cataract is particularly serious because it has the potential for inhibiting visual development, resulting in permanent blindness. Inherited cataracts represent a major contribution to congenital cataracts, especially in developed countries. While cataract represents a common end stage of mutations in a potentially large number of genes acting through varied mechanisms in practice most inherited cataracts have been associated with a subgroup of genes encoding proteins of particular importance for the maintenance of lens transparency and homeostasis. The increasing availability of more detailed information about these proteins and their functions and is making it possible to understand the pathophysiology of cataracts and the biology of the lens in general.

CHMP4B, a novel gene for autosomal dominant cataracts linked to chromosome 20q

Cataracts are a clinically diverse and genetically heterogeneous disorder of the crystalline lens and a leading cause of visual impairment. Here we report linkage of autosomal dominant "progressive childhood posterior subcapsular" cataracts segregating in a white family to short tandem repeat (STR) markers D20S847 (LOD score [Z] 5.50 at recombination fraction [theta] 0.0) and D20S195 (Z=3.65 at theta =0.0) on 20q, and identify a refined disease interval (rs2057262-(3.8 Mb)-rs1291139) by use of single-nucleotide polymorphism (SNP) markers. Mutation profiling of positional-candidate genes detected a heterozygous transversion (c.386A-->T) in exon 3 of the gene for chromatin modifying protein-4B (CHMP4B) that was predicted to result in the nonconservative substitution of a valine residue for a phylogenetically conserved aspartic acid residue at codon 129 (p.D129V). In addition, we have detected a heterozygous transition (c.481G-->A) in exon 3 of CHMP4B cosegregating with autosomal dominant posterior polar cataracts in a Japanese family that was predicted to result in the missense substitution of lysine for a conserved glutamic acid residue at codon 161 (p.E161K). Transfection studies of cultured cells revealed that a truncated form of recombinant D129V-CHMP4B had a different subcellular distribution than wild type and an increased capacity to inhibit release of virus-like particles from the cell surface, consistent with deleterious gain-of-function effects. These data provide the first evidence that CHMP4B, which encodes a key component of the endosome sorting complex required for the transport-III (ESCRT-III) system of mammalian cells, plays a vital role in the maintenance of lens transparency.

Autosomal recessive juvenile onset cataract associated with mutation in BFSP1

A genome wide scan in a consanguineous family of Indian origin with autosomal recessive developmental cataracts was performed by two-point linkage analysis with 382 microsatellite markers. It showed linkage to markers on chromosome 20q, between D20S852 and D20S912, with a maximum lod score of 5.4 obtained with D20S860. This region encompasses the beaded filament structural protein 1 (BFSP1) gene. Direct sequencing revealed a 3343 bp deletion including exon 6 (c.736-1384_c.957-66 del) predicted to result in a shift of the open reading frame. This mutation was absent in 50 control individuals from south India. This is the first report of a mutation in the BFSP1 gene associated with human inherited cataracts. This further increases the genetic heterogeneity of inherited cataracts and provides clues as to the importance of BFSP1 in the cell biology of intermediate filaments and their role in the eye lens.

Markers of inflammation, vascular endothelial dysfunction, and age-related cataract

PURPOSE

To examine the associations of systemic markers of inflammatory disease and vascular endothelial dysfunction with three types of age-related cataract.

DESIGN

Cross-sectional analyses of data from a population-based sample of adults.

METHODS

Standardized protocols for blood collection, measurement of markers, administration of a questionnaire, and grading of lens photographs to determine cataract were used. Univariable and multivariable analyses were performed.

SETTINGS

Cohort in Beaver Dam, Wisconsin.

STUDY POPULATION

A random sample of 396 persons who were > or =50 years of age.

MAIN OUTCOME MEASURE

Prevalent age-related nuclear, cortical, and posterior subcapsular cataract.

RESULTS

Interleukin-6 and intracellular adhesion molecule-1 were associated significantly with prevalent nuclear cataract (odds ratio for each quartile, 1.45 and 2.17, respectively). Many of the associations of markers with cataract types were not linear. There were no significant associations between the markers and cortical or posterior subcapsular cataract.

CONCLUSION

Two serum markers of systemic inflammation and vascular endothelial dysfunction were associated with nuclear cataract.

Locus heterogeneity in autosomal recessive congenital cataracts: linkage to 9q and germline HSF4 mutations

Isolated (non-syndromic) congenital cataract may be inherited as an autosomal dominant, autosomal recessive, or X-linked recessive trait. Considerable progress has been made in identifying genes and loci for dominantly inherited cataract, but the molecular basis for autosomal recessive disease is less well defined. Hence we undertook genetic linkage studies in four consanguineous Pakistani families with non-syndromic autosomal recessive congenital cataracts. In two families linkage to a 38 cM region 9q13-q22 was detected. Although a locus for recessive congenital cataracts had not been mapped previously to this region, the target interval encompasses the candidate region autosomal recessive adult-onset pulverulent cataracts (CAAR). The CAAR was mapped previously to 9q13-q22, and may therefore be allelic to non-syndromic autosomal recessive congenital cataracts. The other two families did not demonstrate linkage to 9q, but both had a region of homozygosity at 16q22 containing the heat shock transcription factor 4 (HSF4) gene. The HSF4 mutations have been reported in four families with autosomal dominant cataracts and, recently, in a single kindred with autosomal recessive congenital cataract. Mutation analysis of HSF4 revealed homozygous mutations (p.Arg175Pro and c.595_599delGGGCC, respectively) in the two families. These findings confirm that mutations in HSF4 may result in both autosomal dominant and autosomal recessive congenital cataract, and highlight the locus heterogeneity in autosomal recessive congenital cataract.

Molecular genetics of age-related cataract

Advances in molecular biological and genetic technology have greatly accelerated elucidation of the genetic contribution to age-related cataract. Epidemiological studies have documented tendencies for cataracts to occur more frequently in relatives of cataract patients than in the general population, genetic studies have demonstrated contributory roles of some specific genes in age related cataract in small populations, and molecular studies have shown changes in expression of specific genes in cataractous lenses. Together, these studies are beginning to provide a conceptual framework for understanding age-related cataracts.

Cell death triggered by a novel mutation in the alphaA-crystallin gene underlies autosomal dominant cataract linked to chromosome 21q

Hereditary cataract is a clinically and genetically heterogeneous lens disease that accounts for a significant proportion of visual impairment and blindness in childhood. The alphaA-crystallin (CRYAA) gene (CRYAA) encodes a member of the small-heat-shock protein (sHSP) family of molecular chaperones and is primarily and abundantly expressed in the ocular lens. Here, we have used linkage analysis to identify a novel missense mutation in CRYAA that underlies an autosomal dominant form of 'nuclear' cataract segregating in a four-generation Caucasian family. A maximum two-point LOD score (Z(max)) of 2.19 (maximum recombination fraction, theta(max)=0) and multipoint Z(max) of 3.3 (theta(max)=0) was obtained at marker D21S1885. Haplotype analysis indicated that the disease gene lay in the approximately 2.7 Mb physical interval between D21S1912 and D21S1260 flanking CRYAA on 21q22.3. Sequence analysis identified a C --> T transition in exon 1 of CRYAA from affected individuals that was predicted to result in the nonconservative substitution of cysteine for arginine at codon 49 (R49C). Transfection studies of lens epithelial cells revealed that, unlike wild-type CRYAA, the R49C mutant protein was abnormally localized to the nucleus and failed to protect from staurosporine-induced apoptotic cell death. This study has identified the first dominant cataract mutation in CRYAA located outside the phylogenetically conserved 'alpha-crystallin core domain' of the sHSP family.

Molecular genetic basis of inherited cataract and associated phenotypes

Congenital cataract is a leading cause of visual disability in children. Inherited isolated (non-syndromic) cataract represents a significant proportion of cases and recently many causative genetic mutations have been identified. Inherited cataract is known to be clinically and genetically heterogeneous. Eleven clear-cut cataract phenotypes have been described. Cataract may be inherited as autosomal dominant, autosomal recessive, or X-linked recessive traits, and 12 loci and 15 specific genes associated with inherited isolated cataract have been identified to date; it is likely that more genes remain to be discovered. The identification of remaining genes will not only improve our understanding of the mechanism of cataract formation but will shed new light on the developmental biology and biochemistry of the lens. Furthermore, it is possible that some of these genes will be implicated in the more common age related cataract, which also has a genetic component to its etiology.

Genetics of childhood cataract

PURPOSE OF REVIEW

Congenital cataracts, although much less common than their age-related counterparts, account for one-tenth of cases of childhood blindness. Approximately half are inherited, either in isolation or as part of a syndrome of ocular or systemic anomalies. This article reviews recent advances made in understanding the molecular genetic basis of isolated, nonsyndromic inherited cataract.

RECENT FINDINGS

New disease-causing mutations continue to be identified and now encompass genes encoding a wide variety of different lens proteins. More detailed investigations of the functional consequences of each mutation are being reported and suggest that lens opacification results not only from precipitation and amyloid-like accumulation of proteins essential for lens transparency but also from interference with their secondary functions.

SUMMARY

Improved functional characterization of mutations causing childhood cataract will improve understanding of lens development and physiology but will also have implications for the more common age-related cataract. This too has a significant genetic component to its etiology, and genes causing monogenic forms of childhood inherited cataract represent excellent candidate genes for age-related cataract. The identification of the genes conferring increased risk of developing age-related cataract will bring closer the development of a medical treatment to delay the onset of lens opacification and need for surgery.

The morphology and natural history of childhood cataracts

The morphology of congenital cataract reflects a combination of the timing and nature of the cause, the anatomy of the lens including its capsule, its development, and changes that take place with time. Morphology may variably affect prognosis, give a clue to the etiology and the age of onset and, in an isolated case, sometimes suggest heritability. The spectrum of morphological variations is enormous and can be complex. A comprehensive approach is to classify the variations according to the area of the lens involved, and sub-dividing them by a detailed description of the shape and appearance. Each specific morphological type is then analyzed determining the etiology, visual prognosis, and management. The use of gene markers has allowed many of these variations to be identified and categorized. Cataracts in childhood can involve the whole lens, in which case they are called total, Morgagnian, or disk-like. They can affect only the center of the lens: lamellar, nuclear, oil droplet, cortical, or coronary. They can be anterior: anterior polar, anterior subcapsular, or anterior lenticonus. The posterior aspect of the lens can also be affected in different fashions: Mittendorf's dot, posterior lenticonus, posterior cortical cataracts, or posterior subcapsular. There are five more forms that must be described separately: punctuate lens opacities, sutural cataracts, coralliform or crystalline, wedge-shaped, and persistent hyperplastic primary vitreous.

A missense mutation in the LIM2 gene is associated with autosomal recessive presenile cataract in an inbred Iraqi Jewish family

In an inbred Iraqi Jewish family, we have studied three siblings with presenile cataract first noticed between the ages of 20 and 51 years and segregating in an autosomal recessive mode. Using microsatellite repeat markers in close proximity to 25 genes and loci previously associated with congenital cataracts in humans and mice, we identified five markers on chromosome 19q that cosegregated with the disease. Sequencing of LIM2, one of two candidate genes in this region, revealed a homozygous T-->G change resulting in a phenylalanine-to-valine substitution at position 105 of the protein. To our knowledge, this constitutes the first report, in humans, of cataract formation associated with a mutation in LIM2. Studies of late-onset single-gene cataracts may provide insight into the pathogenesis of the more common age-related cataracts.