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PurposeThe Pakistan Punjab population has been a rich source for identifying genes causing or contributing to autosomal recessive retinal degenerations (arRD). This study was carried out to delineate the genetic architecture of arRD in the Pakistani population.MethodsThe genetic origin of arRD in a total of 144 families selected only for having consanguineous marriages and multiple members affected with arRD was examined. Of these, causative mutations had been identified in 62 families while only the locus had been identified for an additional 15. The remaining 67 families were subjected to homozygosity exclusion mapping by screening of closely flanking microsatellite markers at 180 known candidate genes/loci followed by sequencing of the candidate gene for pathogenic changes.ResultsOf these 67 families subjected to homozygosity mapping, 38 showed homozygosity for at least one of the 180 regions, and sequencing of the corresponding genes showed homozygous cosegregating mutations in 27 families. Overall, mutations were detected in approximately 61.8 % (89/144) of arRD families tested, with another 10.4% (15/144) being mapped to a locus but without a gene identified.ConclusionsThese results suggest the involvement of unmapped novel genes in the remaining 27.8% (40/144) of families. In addition, this study demonstrates that homozygosity mapping remains a powerful tool for identifying the genetic defect underlying genetically heterogeneous arRD disorders in consanguineous marriages for both research and clinical applications.

PurposeTo localize and identify the gene and mutations causing autosomal recessive retinal dystrophy in two consanguineous Pakistani families.MethodsConsanguineous families from Pakistan were ascertained to be affected with autosomal recessive retinal degeneration. All affected individuals underwent thorough ophthalmologic examinations. Blood samples were collected, and genomic DNA was extracted using a salting out procedure. Genotyping was performed using microsatellite markers spaced at approximately 10 cM intervals. Two-point linkage analysis was performed with the lod score method. Direct DNA sequencing of amplified genomic DNA was performed for mutation screening of candidate genes.ResultsGenome-wide linkage scans yielded a lod score of 3.05 at θ=0 for D17S1832 and 3.82 at θ=0 for D17S938, localizing the disease gene to a 12.22 cM (6.64 Mb) region flanked by D17S1828 and D17S1852 for family 61032 and family 61227, which contains aryl hydrocarbon receptor interacting protein-like 1 (AIPL1), a gene previously implicated in recessive Leber congenital amaurosis and autosomal dominant cone-rod dystrophy. Sequencing of AIPL1 showed a homozygous c.773G>C (p.Arg258Pro) sequence change in all affected individuals of family 61032 and a homozygous c.465G>T (p.(H93_Q155del)) change in all affected members of family 61227.ConclusionsThe results strongly suggest that the c.773G>C (p.R258P) and c.465G>T (p.(H93_Q155del)) mutations in AIPL1 cause autosomal recessive retinal degeneration in these consanguineous Pakistani families.

Purpose: To localize and identify the gene and mutations causing autosomal recessive retinal dystrophy in two consanguineous Pakistani families., Methods: Consanguineous families from Pakistan were ascertained to be affected with autosomal recessive retinal degeneration. All affected individuals underwent thorough ophthalmologic examinations. Blood samples were collected, and genomic DNA was extracted using a salting out procedure. Genotyping was performed using microsatellite markers spaced at approximately 10 cM intervals. Two-point linkage analysis was performed with the lod score method. Direct DNA sequencing of amplified genomic DNA was performed for mutation screening of candidate genes., Results: Genome-wide linkage scans yielded a lod score of 3.05 at θ=0 for D17S1832 and 3.82 at θ=0 for D17S938, localizing the disease gene to a 12.22 cM (6.64 Mb) region flanked by D17S1828 and D17S1852 for family 61032 and family 61227, which contains aryl hydrocarbon receptor interacting protein-like 1 (AIPL1), a gene previously implicated in recessive Leber congenital amaurosis and autosomal dominant cone-rod dystrophy. Sequencing of AIPL1 showed a homozygous c.773G>C (p.Arg258Pro) sequence change in all affected individuals of family 61032 and a homozygous c.465G>T (p.(H93_Q155del)) change in all affected members of family 61227., Conclusions: The results strongly suggest that the c.773G>C (p.R258P) and c.465G>T (p.(H93_Q155del)) mutations in AIPL1 cause autosomal recessive retinal degeneration in these consanguineous Pakistani families.

Purpose: Aniridia is phenotyically and genetically heterogeneous. This study is to summarize the phenotypes and identify the genetic defect responsible for aniridia and congenital progressive cataract in a three generation Chinese family., Methods: A detailed family history and clinical data from patients were collected by ophthalmologic examination, including visual acuity, slit-lamp examination, tonometer, keratometry, corneal topography, optical coherence tomography, and ultrasonic A/B scan. All exons and flanking intronic sequences of the paired box 6 (PAX6) gene were amplified by polymerase chain reaction (PCR) and screened for mutation by direct DNA sequencing. Structure and function of the mutant PAX6 were analyzed by bioinformatics analysis., Results: All the six patients shared common manifestations of complete aniridia, congenital cataract and thickened cornea, and broad phenotypic variability was observed in nystagmus, ptosis, strabismus, glaucoma, corneal pannus, corneal curvature, corneal vascularization, cataract subtype, ectopia lentis, axial length, and optic disc anomalies. Sequencing of the candidate gene detected a heterozygous c.307C>T transition in the coding region of PAX6, resulting in the substitution of a highly conserved arginine codon for a termination codon (p.R103X). The p.P103X mutation co-segregated with the affected individuals in the family. The change was supposed to cause structural and functional changes based on computational analysis., Conclusions: We identified a recurrent PAX6 c.307C>T mutation in an aniridia and congenital progressive cataract family, and summarized the variable phenotypes among the patients, which expanded the phenotypic spectrum of aniridia in a different ethnic background.

Purpose: To identify the underlying genetic defect in four generations of a Chinese family affected with bilateral congenital posterior subcapsular cataracts., Methods: Clinical data from patients in the family were recorded by slit-lamp photography. Genomic DNA samples were extracted from peripheral blood of the pedigree members. Mutation screening was performed in the candidate gene by bidirectional sequencing of the amplified products. The mutation was verified by restriction fragment length polymorphism (RFLP) analysis., Results: The congenital cataract phenotype of the pedigree was identified as posterior subcapsular by slit-lamp photography. Sequencing of the candidate genes detected a heterozygous c.5C→T change in the coding region of the βB2-crystallin gene (CRYBB2), resulting in the substitution of a highly conserved alanine to valine (p. A2V). All nine family members affected with cataracts were positive for this change, but it was not observed in any of the unaffected members of the family. The transition resulted in the loss of a HaeIII restriction site in the affected members of the pedigree, which was present in the unaffected family members and in all of the 100 unrelated individuals tested., Conclusions: This study has identified a novel CRYBB2 gene mutation, resulting in the amino substitution p. A2V in a Chinese family with posterior subcapsular congenital cataracts. This mutation is probably the causative lesion for the observed phenotype in this family.

Purpose: To investigate the consequence of a major intrinsic protein MIP splice-site mutation (c.607-1G>A) in a four-generation Chinese pedigree afflicted with autosomal dominant congenital cataracts (ADCC)., Methods: Both a mutated minigene with c.607-1G>A, and a wild-type minigene were constructed using the pTARGET mammalian expression vector. They were transiently transfected into HeLa cells and human lens epithelial cells, respectively. After 48 h incubation, RNA extraction and RT-PCR analysis were performed and PCR products were separated and confirmed by sequencing. Structural models of the wild-type and the mutant aquaporin 0 (AQP0) were generated and analyzed using SWISS-MODEL., Results: The G>A transition activated a cryptic acceptor splice site (c.965-966) in the 3' untranslated region (3' UTR), resulting in the absence of the coding region and most of the 3'UTR in exon 4 of the mature mRNA. Moreover, homology modeling of the mutant protein suggested that the sixth transmembrane helix and carboxyl terminus were replaced with the Leu-His-Ser tripeptide (AQP0-LHS)., Conclusions: The MIP splice-site mutation (c.607-1G>A) activates a cryptic acceptor splice site in the 3' UTR, which may result in substitution of the sixth transmembrane helix and carboxyl terminus for AQP0-LHS. To our knowledge, this is the first report of activation of a cryptic splice site in the 3' UTR in a human disease gene.

Purpose: To detect the underlying genetic defect in a Chinese family affected with bilateral congenital cataracts., Methods: A detailed family history and clinical data were recorded. Mutation screening was performed in the nuclear cataract-related gene by bidirectional sequencing of the amplified products. The mutation was verified by denaturing high-performance liquid chromatography (DHPLC)., Results: Two cataract phenotypes were observed within this family: one eye exhibited Y-suture and nuclear pulverulent opacification of the lens, while the others exhibited complete opacification in the fetal nuclear region. Sequencing of the candidate genes detected a heterozygous c.319G>A change in the coding region of the major intrinsic protein (MIP), resulting in the substitution of a highly conserved Valine by Isoleucine (p.V107I).The mutation was confirmed by DHPLC., Conclusions: This study has identified a novel MIP mutation, p.V107I in a Chinese family with congenital cataracts. To the best of our knowledge, this is the first reported case of cataracts caused by a mutation in the second extracellular loop domain of MIP.

Purpose: Lens epithelial cell (LEC) apoptosis reduces the formation of posterior capsular opacification (PCO). The involvement of caveolin-1 in the regulation of apoptosis has been previously demonstrated in epithelial cells. In this study, we investigated the relationship between caveolin-1 and apoptosis of LECs under high glucose (HG) concentrations to explore a mechanism in the formation of PCO in diabetic patients., Methods: LECs were treated with high concentrations of glucose with or without epidermal growth factor (EGF) or simvastatin in Dulbecco's Modified Eagle's Medium (DMEM). Induction of apoptosis was measured by flow cytometry, and the expression of caveolin-1 was examined by immunofluorescence microscopy, quantitative real-time reverse transcription polymerase chain reaction (RT-PCR), and immunoblotting., Results: The expression of caveolin-1 was decreased, and the rate of apoptosis was increased in LECs treated with increased glucose concentration and treatment duration. When simvastatin or EGF was added to HG-treated LECs, caveolin-1 levels increased and the apoptosis rate of LECs decreased. Furthermore, colocalization of caveolin-1 and phosphatidylserine (PS) on the cell surfaces of apoptotic LECs was observed by immunofluorescence microscopy., Conclusions: We observed that in HG-treated LECs, caveolin-1 expression decreased and apoptosis increased and that simvastatin or EGF promoted the proliferation of HG-treated LECs. Although the mechanisms for the formation of PCO after cataract surgery in diabetic patients are complex, our results suggest that a high concentration of glucose is not a direct cause. The observation that simvastatin inhibited the apoptosis of HG-treated LECs in its therapeutic concentration suggests that daily dosage of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor used by diabetic patients may increase PCO formation.

Purpose: To map the locus and identify the gene causing autosomal dominant congenital cataract (ADCC) with "snail-like" phenotype in a large Chinese family., Methods: Clinical and ophthalmologic examinations were conducted on family members and documented by slit lamp photography. Linkage analysis was performed with an initial 41 microsatellite markers, then 3 additional markers flanking the major intrinsic protein (MIP) gene. Mutations were screened by DNA sequencing and verified by restriction fragment length polymorphism (RFLP) analysis., Results: Significant two-point LOD scores were obtained at 5 markers flanking MIP with the highest 3.08 (theta=0.00) at marker D12S1632. Mutation screening of MIP identified a heterozygous G>A transition at the acceptor splice site of intron 3 (IVS3 -1 G>A), abolishing a BstSF I restriction site in one allele of all the affected individuals., Conclusions: We identified a novel splice-site mutation (IVS3 -1 G>A in MIP) in a Chinese ADCC family. To our knowledge, this is the first report on an acceptor splice-site mutation in human genes associated with ADCC.

Purpose: To identify the genetic defect associated with autosomal dominant congenital nuclear cataract in a Chinese family., Methods: Family history and phenotypic data were recorded, and the phenotypes were documented by slit lamp photography. The genomic DNA was extracted from peripheral blood leukocytes. All the exons and flanking intronic sequences of CRYGC and CRYGD were amplified by polymerase chain reaction (PCR) and screened for mutation by direct DNA sequencing. Structural models of the wild type and mutant gammaC-crystallin were generated and analyzed by SWISS-MODEL., Results: Sequencing of the coding regions of CRYGC and CRYGD showed the presence of a heterozygous C>A transversion at c.327 of the coding sequence in exon 3 of CRYGC (c.327C>A), which results in the substitution of a wild type cysteine to a nonsense codon (C109X). One and a half Greek key motifs at the COOH-terminus were found to be absent in the structural model of the mutant truncated gammaC-crystallin., Conclusions: A novel nonsense mutation in CRYGC was detected in a Chinese family with consistent autosomal dominant congenital nuclear cataract, providing clear evidence of a relationship between the genotype and the corresponding cataract phenotype.

Purpose: To identify mutations in the fibrillin-1 gene (FBN1) and provide further information about genotype-phenotype correlations in Chinese patients with predominant ectopia lentis (EL) and marfanoid habitus., Methods: Patients from seven Chinese families underwent complete physical, ophthalmic, and cardiovascular examination. Genomic DNA was extracted from leukocytes of peripheral blood from the patients. The 65 exons and flanking intronic sequences of FBN1 were amplified by polymerase chain reaction (PCR) and screened for mutation by direct DNA sequencing., Results: Three novel mutations, c.203G>T in exon 2, c.502T>C in exon 5, and c.2096G>C in exon 16 as well as four known mutations, c.364C>T in exon 4, c.1633C>T in exon 13, c.1879C>T in exon 15, and c.4588C>T in exon37, were identified in FBN1., Conclusions: We identified three novel mutations and four known mutations in FBN1 and found cysteine substitution highly related to EL. These results expand the mutation spectrum in FBN1 and enrich our knowledge of genotype-phenotype correlations due to FBN1 mutations. To our knowledge, this is the first report of cysteine residue loss in the unique NH2-terminal domain of fibrillin-1.