Loss of Caveolin-1 Impairs Light Flicker-Induced Neurovascular Coupling at the Optic Nerve Head.

Glaucoma is a neurodegenerative disease, which results in characteristic visual field defects. Intraocular pressure (IOP) remains the main risk factor for this leading cause of blindness. Recent studies suggest that disturbances in neurovascular coupling (NVC) may be associated with glaucoma. The resultant imbalance between vascular perfusion and neuronal stimulation in the eye may precede retinal ganglion cell (RGC) loss and increase the susceptibility of the eye to raised IOP and glaucomatous degeneration. Caveolin-1 (Cav-1) is an integral scaffolding membrane protein found abundantly in retinal glial and vascular tissues, with possible involvement in regulating the neurovascular coupling response. Mutations in Cav-1 have been identified as a major genetic risk factor for glaucoma. Therefore, we aim to evaluate the effects of Cav-1 depletion on neurovascular coupling, retinal vessel characteristics, RGC density and the positive scotopic threshold response (pSTR) in Cav-1 knockout (KO) versus wild type C57/Bl6 mice (WT). Following light flicker stimulation of the retina, Cav-1 KO mice showed a smaller increase in perfusion at the optic nerve head and peripapillary arteries, suggesting defective neurovascular coupling. Evaluation of the superficial capillary plexus in Cav-1 KO mice also revealed significant differences in vascular morphology with higher vessel density, junction density and decreased average vessel length. Cav-1 KO mice exhibited higher IOP and lower pSTR amplitude. However, there was no significant difference in RGC density between Cav-1 KO and wild type mice. These findings highlight the role of Cav-1 in regulating neurovascular coupling and IOP and suggest that the loss of Cav-1 may predispose to vascular dysfunction and decreased RGC signaling in the absence of structural loss. Current treatment for glaucoma relies heavily on IOP-lowering drugs, however, there is an immense potential for new therapeutic strategies that increase Cav-1 expression or augment its downstream signaling in order to avert vascular dysfunction and glaucomatous change.

CYP1B1 and MYOC Mutations in Vietnamese Primary Congenital Glaucoma Patients.

PURPOSE: Primary congenital glaucoma (PCG, OMIM 231300), the most common glaucoma in infancy, is caused by developmental defects in the anterior chamber angle. The 3 implicated genes are cytochrome P450 family I subfamily B polypeptide 1 (CYP1B1), latent transforming growth factor ß-binding protein 2 (LTBP2), and myocilin (MYOC). In this study, we sought to determine CYP1B1 and MYOC sequence variations in a Vietnamese cohort of index cases with PCG and their families. METHODS: Thirty Vietnamese subjects with PCG and 120 normal Vietnamese subjects were recruited. PCG was defined by the presence of at least 2 of the following clinical manifestations: increased corneal diameter (>10 mm at birth), corneal edema, Haab's striae, optic disc changes, and absence of other ocular or systemic diseases associated with childhood glaucoma. The coding exons, intron and exon boundaries, and untranslated regions of CYP1B1 and MYOC genes were PCR amplified and subjected to bidirectional sequencing in all subjects. RESULTS: We identified 2 homozygous and 3 heterozygous CYP1B1 sequence alterations in our study subjects. Among the 5 mutations identified, 2 (p.H279L and p.L283F) were novel mutations, whereas 3 (p.A121_S122insDRPAFA, p.L107V, and p.V320L) had been previously reported in PCG cases. None of these mutations was observed in any of the 120 controls. Haplotypes generated with 6 non-disease-causing intragenic single nucleotide polymorphisms detected in CYP1B1 indicated that the most common haplotype in Vietnamese population is similar to that found in Chinese and Japanese. The genotype-phenotype correlation showed no significant difference between mutation and no-mutation groups for quantitative clinical features (presenting intraocular pressure, corneal diameter, number of surgeries performed, the cup-to-disc ratio) as well as for qualitative factors (bilateral cases, phenotype severity, and the prognosis) (P>0.05). CONCLUSIONS: Five out of 30 families with PCG (16.7%) had disease attributable to CYP1B1 alterations suggesting that CYP1B1 is not the major gene causing PCG in Vietnamese unlike in the case of Arab or Romany patients. This percentage is similar to that detected in studies of Japanese and Chinese patients with sporadic PCG. PCG has proven to be an ocular disease of genetic heterogeneity, calling for further studies to identify novel genes causing this disease.

ABCC5, a gene that influences the anterior chamber depth, is associated with primary angle closure glaucoma.

Anterior chamber depth (ACD) is a key anatomical risk factor for primary angle closure glaucoma (PACG). We conducted a genome-wide association study (GWAS) on ACD to discover novel genes for PACG on a total of 5,308 population-based individuals of Asian descent. Genome-wide significant association was observed at a sequence variant within ABCC5 (rs1401999; per-allele effect size =  -0.045 mm, P = 8.17 × 10(-9)). This locus was associated with an increase in risk of PACG in a separate case-control study of 4,276 PACG cases and 18,801 controls (per-allele OR = 1.13 [95% CI: 1.06-1.22], P = 0.00046). The association was strengthened when a sub-group of controls with open angles were included in the analysis (per-allele OR = 1.30, P = 7.45 × 10(-9); 3,458 cases vs. 3,831 controls). Our findings suggest that the increase in PACG risk could in part be mediated by genetic sequence variants influencing anterior chamber dimensions.

Genome-wide association analyses identify three new susceptibility loci for primary angle closure glaucoma.

Primary angle closure glaucoma (PACG) is a major cause of blindness worldwide. We conducted a genome-wide association study including 1,854 PACG cases and 9,608 controls across 5 sample collections in Asia. Replication experiments were conducted in 1,917 PACG cases and 8,943 controls collected from a further 6 sample collections. We report significant associations at three new loci: rs11024102 in PLEKHA7 (per-allele odds ratio (OR)=1.22; P=5.33×10(-12)), rs3753841 in COL11A1 (per-allele OR=1.20; P=9.22×10(-10)) and rs1015213 located between PCMTD1 and ST18 on chromosome 8q (per-allele OR=1.50; P=3.29×10(-9)). Our findings, accumulated across these independent worldwide collections, suggest possible mechanisms explaining the pathogenesis of PACG.

Molecular analysis of CHX10 and MFRP in Chinese subjects with primary angle closure glaucoma and short axial length eyes.

PURPOSE: The genetic basis of primary angle closure glaucoma (PACG) has yet to be elucidated. Ocular characteristics related to PACG such as short hyperopic eyes with shallow anterior chambers suggest the involvement of genes that regulate ocular size. CHX10, a retinal homeobox gene associated with microphthalmia, and MFRP, the membrane-type frizzled-related protein gene underlying recessive nanophthalmos, represent good candidate genes for PACG due to the association with small eyes. To investigate the possible involvement of CHX10 and MFRP in PACG, we sequenced both genes in PACG patients with small ocular dimensions. METHODS: One hundred and eight Chinese patients with axial lengths measuring 22.50 mm or less were selected for analysis. Ninety-three age- and ethnically-matched control subjects were also screened. Genomic DNA was extracted from leukocytes of peripheral blood samples, and the exons of CHX10 and MFRP were amplified by polymerase chain reaction (PCR) and subjected to bidirectional sequencing and analysis. RESULTS: All study patients were Chinese with a mean age of 66.2+/-9.1 years (range 46-86). There were 77 females (71.3%). Forty-nine out of the one hundred and eight subjects had previous symptomatic PACG, and 59 had asymptomatic PACG. The mean axial length was 21.90+/-0.50 mm (range 19.98-22.50 mm). We identified a possible disease-causing variant in CHX10 (c.728G>A) resulting in Gly243Asp substitution in one patient. This variant was not found in 215 normal controls. Several CHX10 and MFRP polymorphisms were also identified. CONCLUSIONS: Our results do not support a significant role for CHX10 or MFRP mutations in PACG.

Lack of association between the rs2664538 polymorphism in the MMP-9 gene and primary angle closure glaucoma in Singaporean subjects.

PURPOSE: A recent study identified the single nucleotide polymorphism (SNP) rs2664538 within the MMP-9 gene with risk for acute primary angle closure glaucoma (PACG). The aim of this study was to confirm this association in Singaporean Chinese subjects with both acute and chronic PACG. METHODS: This was an observational cross-sectional study. Genomic DNA was extracted from leukocytes of peripheral blood and genotypes were determined by polymerase chain reaction and direct sequencing. The association of the SNP with PACG was evaluated using chi tests. RESULTS: A total of 217 subjects with PACG (consisting of 85 acute and 132 chronic PACG), and 83 normal control Chinese subjects were studied. There was no significant difference in the rs2664538 SNP allele frequencies for acute or chronic PACG subjects compared with controls. CONCLUSIONS: This study did not find an association between the rs2664538 polymorphism within the MMP-9 gene and PACG in this sample of Chinese subjects.

Analysis of the posterior polymorphous corneal dystrophy 3 gene, TCF8, in late-onset Fuchs endothelial corneal dystrophy.

PURPOSE: Because the endothelial (posterior) corneal dystrophies share common pathologic features and result from primary endothelial dysfunction, it is possible that a proportion of them could be clinical manifestations of different mutations of the same gene. The aim of our study was to determine whether mutations of the TCF8 gene, recently implicated in posterior polymorphous dystrophy, may also play a role in the development of the more common Fuchs endothelial corneal dystrophy (FECD). METHODS: Genomic DNA was extracted from leukocytes of peripheral blood, and the nine exons of the TCF8 gene were PCR amplified and subjected to bidirectional sequencing and analysis. Samples from 74 unrelated Chinese patients (55 women, 19 men) with a diagnosis of late-onset FECD and 93 age- and race-matched controls were studied. RESULTS: The affected probands ranged in age from 52 to 91 years (mean age, 65.1 years); 8 had familial FECD and 66 had sporadic FECD. The authors found two mutations in the coding region of the TCF8 gene: a novel missense mutation in one patient c.2087A>G in exon 7 (Asn696Ser) and a silent mutation in exon 2 c.192T>C (D64D). CONCLUSIONS: The identification of a novel missense mutation in only one of the patients implied that TCF8 does not play a significant role in the pathogenesis of FECD in this Chinese population.

SLC4A11 mutations in Fuchs endothelial corneal dystrophy.

The endothelial (posterior) corneal dystrophies, which result from primary endothelial dysfunction, include Fuchs endothelial corneal dystrophy (FECD), posterior polymorphous corneal dystrophy (PPCD) and congenital hereditary endothelial dystrophy (CHED). Mutations in SLC4A11 gene have been recently identified in patients with recessive CHED (CHED2). In this study, we show that heterozygous mutations in the SLC4A11 gene also cause late-onset FECD. Four heterozygous mutations [three missense mutations (E399K, G709E and T754M) and one deletion mutation (c.99-100delTC)] absent in ethnically matched controls were identified in a screen of 89 FECD patients. Missense mutations involved amino acid residues showing high interspecies conservation, indicating that mutations at these sites would be deleterious. Accordingly, immunoblot analysis, biochemical assay of cell surface localization and confocal immunolocalization showed that missense proteins encoded by the mutants were defective in localization to the cell surface. Our data suggests that SLC4A11 haploinsufficiency and gradual accumulation of the aberrant misfolded protein may play a role in FECD pathology and that reduced levels of SLC4A11 influence the long-term viability of the neural crest derived corneal endothelial cells.

Novel SLC4A11 mutations in patients with recessive congenital hereditary endothelial dystrophy (CHED2). Mutation in brief #958. Online.

Autosomal recessive congenital hereditary endothelial dystrophy (CHED2) is a severe and rare corneal disorder that presents at birth or shortly thereafter, characterized by corneal opacification and nystagmus. Recently the gene for CHED2 was identified and seven different mutations in the SLC4A11 gene were reported. Here, we report seven novel mutations and two previously identified mutations in families from India and the United Kingdom with recessive CHED. The novel changes include two nonsense (p.Trp240X; p.Gln800X) three missense (p.Glu143Lys; p.Cys386Arg; p.Arg755Trp) and two splice site mutations (c.2240+1G>A; c.2437-1G>A). Interestingly, the c.2398C>T (p.Gln800X) and c.2437-1G>A identified in two affected siblings represent the first compound heterozygous mutations in the SLC4A11 gene.

Lack of association between interleukin-1 gene cluster polymorphisms and glaucoma in Chinese subjects.

PURPOSE: A recent study identified single nucleotide polymorphisms (SNPs) within the IL-1 gene cluster at chromosomal locus 2q13 that were associated with reduced risk for primary open-angle glaucoma (POAG) in whites. The purpose of this study was to investigate the association between IL-1 SNPs and glaucoma in Chinese patients with either POAG or primary-angle closure glaucoma (PACG). METHODS: Patients with POAG with a mean IOP without treatment that was consistently <21 mm Hg on diurnal testing were classified as having normal-tension glaucoma (NTG) and those with higher IOP were classified as having high-tension glaucoma (HTG). Subjects with PACG had at least 180 degrees of angle closure on gonioscopy. Genotypes were determined by polymerase chain reaction and restriction digest enzymes at the following loci: IL1A (-889C/T), IL1B (+3953C/T), and IL1B (-511C/T). The association of individual SNPs with glaucoma was evaluated by using chi(2) testing. Haplotype analysis was performed with the PHASE program, with haplotype frequency estimated for combined cases and controls, assuming Hardy-Weinberg equilibrium (HWE) of haplotypes. RESULTS: Of the Chinese subjects studies, 194 had POAG (94 NTG and 100 HTG), 125 had PACG, and 79 were normal control subjects. There was no significant difference in IL-1 SNP or allele frequencies for in subjects with POAG or PACG compared with control subjects, or between NTG and HTG. None of the common haplotypes showed any significant difference between the HTG, NTG, PACG, and normal control subjects. CONCLUSIONS: This study did not find an association between IL-1 gene cluster polymorphisms and glaucoma in this sample of Chinese subjects.

Mutations in sodium-borate cotransporter SLC4A11 cause recessive congenital hereditary endothelial dystrophy (CHED2).

Congenital hereditary endothelial dystrophy (CHED) is a heritable, bilateral corneal dystrophy characterized by corneal opacification and nystagmus. We describe seven different mutations in the SLC4A11 gene in ten families with autosomal recessive CHED. Mutations in SLC4A11, which encodes a membrane-bound sodium-borate cotransporter, cause loss of function of the protein either by blocking its membrane targeting or nonsense-mediated decay.

Characterization of Bietti crystalline dystrophy patients with CYP4V2 mutations.

PURPOSE: Mutations of the CYP4V2 gene, a novel family member of the cytochrome P450 genes on chromosome 4q35, have recently been identified in patients with Bietti crystalline dystrophy (BCD). The aim of this study was to investigate the spectrum of mutations in this gene in BCD patients from Singapore, and to characterize their phenotype. METHODS: Nine patients with BCD from six families were recruited into the study. The 11 exons of the CYP4V2 gene were amplified from genomic DNA of patients by polymerase chain reaction and then sequenced. Detailed characterization of the patients' phenotype was performed with fundal photography, visual field testing, fundal fluorescein angiography, and electroretinography (ERG). RESULTS: Three pathogenic mutations were identified; two mutations, S482X and K386T, were novel and found in three patients. The third mutation, a previously identified 15-bp deletion that included the 3' splice site for exon 7, was found in all nine patients, with six patients carrying the deletion in the homozygous state. Haplotype analysis in patients and controls indicated a founder effect for this deletion mutation in exon 7. Clinical heterogeneity was present in the patients. Compound heterozygotes for the deletion in exon 7 seemed to have more severe disease compared to patients homozygous for the deletion. There was good correlation between clinical stage of disease and ERG changes, but age did not correlate with disease severity. CONCLUSIONS: This study identified novel mutations in the CYP4V2 gene as a cause of BCD. A high carrier frequency for the 15-bp deletion in exon 7 may exist in the Singapore population. Phenotype characterization showed clinical heterogeneity, and age did not correlate with disease severity.

Molecular analysis of the myocilin gene in Chinese subjects with chronic primary-angle closure glaucoma.

PURPOSE: Mutations in the myocilin (MYOC) gene have been implicated in juvenile as well as late-onset primary open-angle glaucoma (POAG). Overall, MYOC mutations account for 3% to 5% of cases of POAG worldwide, making it the most significant gene identified so far in glaucoma. Although there are some similarities in the phenotype of POAG and in particular chronic primary angle-closure glaucoma (PACG), little is known about the role of MYOC in the causation of PACG. To address this, the MYOC gene was screened in a cohort of 106 patients with chronic PACG. METHODS: Genomic DNA was extracted from leukocytes of the peripheral blood and exons 1 to 3 of the MYOC gene were PCR amplified and subjected to bidirectional sequencing and analysis. RESULTS: One hundred six patients with chronic PACG of Chinese ethnicity were studied. Sequencing of the MYOC gene in these patients revealed eight sequence variants. Of these, one was a nonsense change, three were missense changes, two were synonymous codon changes, and two were changes in noncoding sequences. These included the Arg46Stop and Thr353Ile mutations, which have been reported in individuals with POAG. However, all the sequence alterations identified have been found in normal Chinese subjects. CONCLUSIONS: The results of this study do not support a role for MYOC mutations in the pathogenesis of chronic PACG in the Chinese.