Recessive Congenital Cataracts Research Articles

Novel and known variants in GJA3 and LIM2 in congenital cataract families from North India

BackgroundTo identify the underlying genetic defects in autosomal dominant (ADCC) and autosomal recessive (ARCC) congenital cataract families from North India.MethodsDetailed family histories were collected, pedigrees drawn followed by slit-lamp examination and lens photography. Mutation screening was performed using Sanger sequencing in the known candidate genes for crystallins, connexins, and membrane proteins. The pathogenicity of identified variants was assessed bioinformatically.ResultsIn two ADCC families (CC-281 and CC-3015) with posterior lenticonus cataract, a novel change c.263C > T (p.P88L) in GJA3 in CC-281 family and a previously reported substitution c.388C > T (p.R130C) in LIM2 in CC-3015 family was observed. In an ARCC family (CC-3005) having central pulverulent cataract, a novel frameshift deletion (c.764delT;p.L255R46fs) in GJA3 was detected. The observed variants segregated completely with phenotypes in the affected members and were neither present in unaffected family members nor in the ethnically matched 150 controls (tested for two novel variants), hence excluding these as polymorphisms.ConclusionsPresent study identified two novel mutations i.e., c.263C > T;p.P88L and c.764delT;p.L255R46fs in GJA3 in an ADCC and an ARCC family having posterior lenticonus and central pulverulent cataract, respectively. In another ADCC family with posterior lenticonus cataract, a previously reported mutation c.388C > T;p.R130C in LIM2 was observed. R130 may be a mutation hotspot as previously ADCC families from different ethnicities (UK/Czechia, China, Spain, Japan) also harbored the same substitution, however, with different phenotypes i.e., nuclear pulverulent, membranous, nuclear, lamellar, and sutural/lamellar. Findings in present study thus expand the mutation spectrum and phenotypic heterogeneity linked with GJA3 and LIM2.

Autosomal recessive congenital cataract is associated with a novel 4-bp splicing deletion mutation in a novel C10orf71 human gene

Congenital cataract is one of the most genetically heterogeneous ocular conditions with different genes involved in its etiology. Here, we describe the analysis of a new candidate gene of a congenital bilateral cataract associated with polymalformative syndrome, moderate global developmental delay, microcephaly, axial hypotonia, intrauterine growth restriction and facial dysmorphism for two affected siblings. Molecular analysis included exome sequencing and genome wide homozygosity mapping revealed a region of homozygosity shared by the two affected siblings at 10q11.23. The new C10orf71 gene was included in this interval and direct sequencing of this gene revealed an already described homozygous c. 2123T > G mutation (p. L708R) for the two affected subjects. Interestingly, we revealed in contrast a 4-bp deletion on the 3'-splicing acceptor site of intron 3-exon 4, namely defined as IVS3-5delGCAA. The C10Orf71 gene expression analysis using RT-PCR showed an expression pattern in different fetal organs and tissues as well as in leukocytes and confirmed that the IVS3-5delGCAA deletion of the C10orf71 gene is a splicing mutation responsible for the shortening of the C10orf71 protein in the two related patients. The C10orf71 gene has not been described to date as associated to the autosomal recessive phenotype.

A genomic deletion encompassing CRYBB2-CRYBB2P1 is responsible for autosomal recessive congenital cataracts

Here we report a consanguineous Pakistani family with multiple affected individuals with autosomal recessive congenital cataract (arCC). Exclusion analysis established linkage to chromosome 22q, and Sanger sequencing coupled with PCR-based chromosome walking identified a large homozygous genomic deletion. Our data suggest that this deletion leads to CRYBB2-CRYBB2P1 fusion, consisting of exons 1–5 of CRYBB2 and exon 6 of CRYBB2P1, the latter of which harbors the c.463 C > T (p.Gln155*) mutation, and is responsible for arCC.

Two New Variants in FYCO1 Are Responsible for Autosomal Recessive Congenital Cataract in Iranian Population.

The purpose of this experimental study was to investigate the genetic etiology of congenital cataract (CC) manifesting an autosomal recessive pattern of inheritance in four Iranian families. Affected individuals and their normal first-degree relatives in each family were included in the present study. The genomic DNA of the blood samples was extracted from all participants, and one affected member belonging to each family was subjected to Whole Exome Sequencing (WES). Using bidirectional Sanger sequencing, the identified variants were validated by co-segregation analysis. Two different mutations were detected in the FYCO1 gene encoding FYVE and coiled-coil domain-containing protein. A previously reported missense mutation, c.265C>T (p.Arg89Cys), was found in one Iranian family for the first time, and a combination of two variants in a single codon, c.[265C>T;267C>A] (p.Arg89X), was identified in the three other families. On the other hand, accompanying the c.265C>T mutation, the presence of the c.267C>A polymorphism leads to a premature stop codon. In-Silico Analysis of FYCO1 protein demonstrated that RUN domain will be interrupted so that the large part of functional protein will be eliminated due to this novel variant. FYCO1 has been proved to be involved in human lens development and transparency. Its mutations, therefore, result in CC. Herein, we reported the first autosomal recessive CC patients with c.265C>T (p.Arg89Cys) or c.[265C>T;267C>A] variant in Iranian population for the FYCO1 gene. FYCO1 mutations could be tracked for preventive objectives or even be targeted as therapeutic candidates via treatment approaches in the future.

A Novel Mutation in the FYCO1 Gene Causing Congenital Cataract: Case Study of a Chinese Family.

Congenital cataract is the most important global cause of visual impairment in children. Autosomal dominant and autosomal recessive inheritance account for the majority of the hereditary nonsyndromic congenital cataract. The function of FYCO1 gene is to guide the transport of the microtubule-directed vesicles. Mutations in the FYCO1 gene may cause cataracts. We reported a novel nonsense mutation in FYCO1 (c.1411C > T, P. R471 ∗), which could cause nonsyndrome autosomal recessive congenital cataract. We underwent an ophthalmology examination of all participants and collected blood samples from all participants and extracted genomic DNAs. By whole exome sequencing, we found that this family carried an unreported mutation in the FYCO1 gene: c.1411C > T, P. R471 ∗. Sanger sequencing was performed to verify the mutation. We used ITASSER and PYMOL to predict and compare the structure and function of the mutated proteins. Using SIFT software and referring to the relevant guidelines of ACMG, the mutation was determined to be pathogenic. The models suggested that the nonsense mutation p.R471∗ resulted in a profound disruption of the FYCO1 protein structure. This report expands the locus information of the FYCO1 mutations.

Targeted gene sequencing of FYCO1 identified a novel mutation in a Pakistani family for autosomal recessive congenital cataract.

BackgroundCongenital cataract is causing one‐third of blindness worldwide. Congenital cataract is heterogeneous in its inheritance patterns. The current study is aimed to explore the unknown genetic causes underlying congenital cataracts.MethodsBlood samples from affected and normal individuals of n = 25 Pakistani families identified with congenital cataracts were collected. Genomic DNA was extracted and Sanger sequencing was performed to identify novel pathogenic variants in the FYCO1 (MIM#607182) gene. Later structural bioinformatics tools and molecular dynamics simulations were performed to analyze the impact of these variants on protein structure and function.ResultsSanger sequencing resulted in the identification of a novel splice site mutation (NM_024513.3: c.3151‐29_3151‐7del) segregating in an autosomal recessive manner. This novel variant was confirmed to be absent in the n = 300 population controls. Further, bioinformatics tools revealed the formation of a mutant protein with a loss of the Znf domain. In addition, we also found a previously known (c.4127 T > C; p.Leu1376Pro) mutation in four families. We also report a novel heterozygous variant (c.3419G > A; p.Arg1140Gln) in another family.ConclusionsIn conclusion, we report a novel deletion (NM_024513.3: c.3151‐29_3151‐7del) in one family and a frequent homozygous missense mutation (c.4127 T > C; p.Leu1376Pro) in four Pakistani families. The current research highlights the importance of autophagy in lens development and maintaining its transparency.

Estimation of the mutation age c.1621C>T p.(Gln541*) in the FYCO1 gene responsible for the development of autosomal recessive congenital cataract in the Yakut population

Estimation of the mutation age c.1621C>T p.(Gln541*) in the FYCO1 gene responsible for the development of autosomal recessive congenital cataract in the Yakut population

A missense allele of PEX5 is responsible for the defective import of PTS2 cargo proteins into peroxisomes

Peroxisomes, single-membrane intracellular organelles, play an important role in various metabolic pathways. The translocation of proteins from the cytosol to peroxisomes depends on peroxisome import receptor proteins and defects in peroxisome transport result in a wide spectrum of peroxisomal disorders. Here, we report a large consanguineous family with autosomal recessive congenital cataracts and developmental defects. Genome-wide linkage analysis localized the critical interval to chromosome 12p with a maximum two-point LOD score of 4.2 (θ = 0). Next-generationexome sequencing identified a novel homozygous missense variant (c.653T > C; p.F218S) in peroxisomal biogenesis factor 5 (PEX5), a peroxisome import receptor protein. This missense mutation was confirmed by bidirectional Sanger sequencing. It segregated with the disease phenotype in the family and was absent in ethnically matched control chromosomes. The lens-specific knockout mice of Pex5 recapitulated the cataractous phenotype. In vitro import assays revealed a normal capacity of the mutant PEX5 to enter the peroxisomal Docking/Translocation Module (DTM) in the presence of peroxisome targeting signal 1 (PTS1) cargo protein, be monoubiquitinated and exported back into the cytosol. Importantly, the mutant PEX5 protein was unable to form a stable trimeric complex with peroxisomal biogenesis factor 7 (PEX7) and a peroxisome targeting signal 2 (PTS2) cargo protein and, therefore, failed to promote the import of PTS2 cargo proteins into peroxisomes. In conclusion, we report a novel missense mutation in PEX5 responsible for the defective import of PTS2 cargo proteins into peroxisomes resulting in congenital cataracts and developmental defects.

Mutation in the Crybb1 gene encoding beta‐B1‐crystallin leads to recessive cataracts in the mouse

PurposeCongenital cataracts are caused by mutations in various genes, and CRYBB1 is one of them. Aim of the study was to create a corresponding mouse model for a cataract‐causing mutation in Crybb1.MethodsThe ENU‐sperm archive of F1 mouse mutants (https://www.helmholtz-muenchen.de/ieg/services/scientific-resources/index.html) was searched for mutations in Crybb1. After selection of an appropriate mutation the corresponding mouse mutant was recovered after in‐vitro fertilization.ResultsWe recently identified a mutation in exon 6 of CRYBB1 (c.613delC; p.Q205Sfs4*) as causative for congenital dominant cataracts in an Indian family. Correspondingly, we established a mouse mutant line, which affects the exon 5 of the Crybb1 gene (c.500A–>T; p.D167V). The mouse mutation affects the 3rd Greek Key motif; correspondingly, the size of the alpha‐helical region and the size of several beta‐sheets might be modified in the mutant protein. PolyPhen‐2 predicted this mutation as “possibly damaging” with a score of 0.731. This mutation leads to a recessive form of cataracts with clear lenses in heterozygotes, although Crybb1 is expressed in mouse lenses from E12.5 onwards. Similar to other beta‐crystallins, Crybb1 is also expressed in the brain, which might lead to additional neuronal changes and might explain the involvement of Crybb1 in association with schizophrenia and stress (Spadaro PA et al., Biol. Psychiatr. 2015;78: 848‐859).ConclusionsIn humans, several cataract‐causing mutations have been identified ‐ most of them leading to dominant cataracts, and only a few of these mutations have been shown to cause a recessive way of inheritance. Here we present the first Crybb1 mouse mutant line suffering from a recessive congenital cataract.

Fine mapping of chromosome 9 locus associated with congenital cataract.

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. 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. 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 7.99cM in this study. Our results reduced the linkage interval of previously reported cataract locus on chromosome 9, thus considerably reducing the number of candidate genes.

Molecular Genetic Analysis of Pakistani Families With Autosomal Recessive Congenital Cataracts by Homozygosity Screening.

PurposeTo identify the genetic origins of autosomal recessive congenital cataracts (arCC) in the Pakistani population.MethodsBased on the hypothesis that most arCC patients in consanguineous families in the Punjab areas of Pakistan should be homozygous for causative mutations, affected individuals were screened for homozygosity of nearby highly informative microsatellite markers and then screened for pathogenic mutations by DNA sequencing. A total of 83 unmapped consanguineous families were screened for mutations in 33 known candidate genes.ResultsPatients in 32 arCC families were homozygous for markers near at least 1 of the 33 known CC genes. Sequencing the included genes revealed homozygous cosegregating sequence changes in 10 families, 2 of which had the same variation. These included five missense, one nonsense, two frame shift, and one splice site mutations, eight of which were novel, in EPHA2, FOXE3, FYCO1, TDRD7, MIP, GALK1, and CRYBA4.ConclusionsThe above results confirm the usefulness of homozygosity mapping for identifying genetic defects underlying autosomal recessive disorders in consanguineous families. In our ongoing study of arCC in Pakistan, including 83 arCC families that underwent homozygosity mapping, 3 mapped using genome-wide linkage analysis in unpublished data, and 30 previously reported families, mutations were detected in approximately 37.1% (43/116) of all families studied, suggesting that additional genes might be responsible in the remaining families. The most commonly mutated gene was FYCO1 (14%), followed by CRYBB3 (5.2%), GALK1 (3.5%), and EPHA2 (2.6%). This provides the first comprehensive description of the genetic architecture of arCC in the Pakistani population.

Deletion at the GCNT2 Locus Causes Autosomal Recessive Congenital Cataracts.

PurposeThe aim of this study is to identify the molecular basis of autosomal recessive congenital cataracts (arCC) in a large consanguineous pedigree.MethodsAll 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.ResultsExclusion 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.ConclusionHere, we report a novel insertion/deletion mutation at the GCNT2 locus that is responsible for congenital cataracts in a large consanguineous family.

Mutation in LIM2 Is Responsible for Autosomal Recessive Congenital Cataracts.

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

PurposeThis study was performed to investigate the genetic determinants of autosomal recessive congenital cataracts in large consanguineous families.MethodsAffected 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.ResultsThe 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.ConclusionHere, we report a common ancestral mutation in CRYBB3 associated with autosomal recessive congenital cataracts identified in four familial cases of Pakistani origin.

A novel homozygous mutation in HSF4 causing autosomal recessive congenital cataract.

Cataract is defined as opacity in the crystalline lens and congenital cataract occurs during the first year of life. Until now, mutations of more than 50 genes in congenital cataract have been reported with various modes of inheritance. Among them, HSF4 mutations have been reported in autosomal dominant, autosomal recessive and age-related forms of cataract. The inheritance patterns of these mutations depend on their mutational positions in HSF4: autosomal dominant or recessive mutations are respectively found either in a DNA-binding domain or in (or downstream of) hydrophobic repeats. Here we report a novel homozygous HSF4 mutation (c.521T>C, p.Leu174Pro) in two affected sibs of an Iranian consanguineous family using whole exome sequencing. The mutation is predicted as highly pathogenic by in silico analysis (SIFT, Polyphen2 and MutationTaster) and is not found in any of control databases. This mutation is located in a hydrophobic repeat of the HSF4 protein, which is consistent with the mode of inheritance as an autosomal recessive trait.

Missense Mutations in CRYAB Are Liable for Recessive Congenital Cataracts.

PurposeThis study was initiated to identify causal mutations responsible for autosomal recessive congenital cataracts in consanguineous familial cases.MethodsAffected 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.ResultsThe 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.ConclusionHere, we report two novel missense mutations, p.R11C and p.R12C, in CRYAB associated with autosomal recessive congenital nuclear cataracts.

SIPA1L3 identified by linkage analysis and whole-exome sequencing as a novel gene for autosomal recessive congenital cataract.

Congenital cataract (CC) is one of the most important causes for blindness or visual impairment in infancy. A substantial proportion of isolated CCs has monogenic causes. The disease is genetically heterogeneous, and all Mendelian modes of inheritance have been reported. We mapped a locus for isolated CC on 19p13.1-q13.2 in a distantly consanguineous German family with two sisters affected by dense white cataracts. Whole-exome sequencing identified a homozygous nonsense variant c.4489C>T (p.(R1497*)) in SIPA1L3 (signal-induced proliferation-associated 1 like 3) in both affected children. SIPA1L3 encodes a GTPase-activating protein (GAP), which interacts with small GTPases of the Rap family via its Rap-GAP-domain. The suggested role of Rap GTPases in cell growth, differentiation and organization of the cytoskeleton in the human lens, and lens-enriched expression of the murine ortholog gene Sipa1l3 in embryonic mice indicates that this gene is crucial for early lens development. Our results provide evidence that sequence variants in human SIPA1L3 cause autosomal recessive isolated CC and give new insight into the molecular pathogenesis underlying human cataracts.

RGS6: a novel gene associated with congenital cataract, mental retardation, and microcephaly in a Tunisian family.

The object of this study is to identify the underlying genetic defect in a consanguineous Tunisian family affected with autosomal recessive congenital cataract associated with mental retardation and microcephaly. A whole-genome scan was performed with polymorphic microsatellites in the axiom data for the screened members. Homozygous regions were analyzed with integrated Systems Tool for Eye gene Discovery (iSyTE), to identify candidate genes with lens-enriched expression that were potentially associated with cataract. Then we screened for mutations by direct sequencing. Structure and function of the mutant gene were analyzed by bioinformatics analysis. Using whole-genome scanning, we identified six runs of homozygosity shared among affected members of the studied family. Analysis of these regions by iSyTE allowed us to select 3 genes (RGS6, PCNX, and P4HA1) according to their expression in 3 critical stages of lens development. Upon screening for mutations by sequencing analysis, we found a novel mutation in RGS6, the splice-acceptor variant c.1369-1G>C that was not previously reported in congenital cataract phenotypes. Our study identified a new gene to be included in the large spectrum of cataract-associated genes. Importantly, the study demonstrated that, in addition to lens-enriched genes that exhibit high expression levels, genes identified by iSyTE that are highly lens-enriched but have lower absolute expression may also represent candidates for potential function in the lens.

Autosomal recessive congenital cataract, intellectual disability phenotype linked to STX3 in a consanguineous Tunisian family.

The aim of this study is to investigate the genetic basis of autosomal recessive congenital cataract and intellectual disability phenotype in a consanguineous Tunisian family. The whole genome scan of the studied family was performed with single nucleotide polymorphisms (SNPs). The resulted runs of homozygosity (ROH) were analyzed through the integrated Systems Tool for Eye gene discovery (iSyTE) in order to prioritize candidate genes associated with congenital cataract. Selected genes were amplified and sequenced. Bioinformatic analysis was conducted to predict the function of the mutant gene. We identified a new specific lens gene named syntaxin 3 linked to the studied phenotype. The direct sequencing of this gene revealed a novel missense mutation c.122A>G which results in p.E41G. Bioinformatic analysis suggested a deleterious effect of this mutation on protein structure and function. Here, we report for the first time a missense mutation of a novel lens specific gene STX3 in a phenotype associating autosomal recessive congenital cataract and intellectual disability.

Homozygosity mapping identifies a GALK1 mutation as the cause of autosomal recessive congenital cataracts in 4 adult siblings

ObjectiveMonogenic congenital cataract is one of the most genetically heterogeneous ocular conditions with almost 30 different genes involved in its etiology. In adult patients, genotype–phenotype correlations are troubled by eye surgery during infancy and/or long-term ocular complications. Here, we describe the molecular diagnosis of GALK1 deficiency as the cause of autosomal recessive congenital cataract in a family from Costa Rica. MethodsFour affected siblings were included in the study. All of them underwent eye surgery during the first decade but medical records were not available. Congenital cataract was diagnosed by report. Molecular analysis included genome wide homozygosity mapping using a 250K SNP Affymetrix microarray followed by PCR amplification and direct nucleotide sequencing of candidate gene. ResultsGenome wide homozygosity mapping revealed a 6Mb region of homozygosity shared by two affected siblings at 17q25. The GALK1 gene was included in this interval and direct sequencing of this gene revealed a homozygous c.1144C>T mutation (p.Q382*) in all four affected subjects. ConclusionsThis work demonstrates the utility of homozygosity mapping in the retrospective diagnosis of a family with congenital cataracts in which ocular surgery at early age, the lack of medical records, and the presence of long term eye complications, impeded a clear clinical diagnosis during the initial phases of evaluation.