DNA sequence variants in the LOXL1 gene are associated with pseudoexfoliation glaucoma in a U.S. clinic-based population with broad ethnic diversity

Eurasian and Sub-Saharan African mitochondrial DNA haplogroup influences pseudoexfoliation glaucoma development in Saudi patients

PURPOSE

To investigate whether different mitochondrial DNA (mtDNA) haplogroups have a role on the development of pseudoexfoliation glaucoma (PEG) in the Saudi Arab population.

METHODS

The mtDNA regulatory region and coding regions comprising mtDNA haplogroup diagnostic polymorphisms were sequenced in patients with PEG (n=94), healthy matched controls (free of PEG; n=112) and a healthy Saudi Arab population group (n=810).

RESULTS

The Eurasian haplogroup T and the Sub-Saharan African Haplogroup L2 confer susceptibility to PEG, whereas the Eurasian haplogroup N1 was associated with reduced risk to develop PEG in the Saudi Arab population.

CONCLUSIONS

Mitochondrial haplogroups T and L2 may play a role in the development of PEG in the Saudi Arabian population.

Analysis of LOXL1 single nucleotide polymorphisms in Polish population with pseudoexfoliation syndrome

PURPOSE

To assess the possible association of lysyl oxidase-like 1 (LOXL1) gene variants with pseudoexfoliation syndrome (PEX) in Polish population.

METHODS

The group studied comprised of 36 patients with PEX (men and women) who presented to Department of Ophthalmology Collegium Medicum UMK in Bydgoszcz, Poland, and 30 control subjects. Blood samples were obtained from each patient via peripheral venipuncture, and genomic DNA was isolated according to the standard procedures. Three LOXL1 single nucleotide polymorphisms (SNPs) rs1048661 (R141L), rs3825942 (G153D) and rs216524 were genotyped in patient sample.

RESULTS

The significant association with PEX was found for the G allele of rs3825942 (p = 0.0047) and for the T allele of rs216541 (p = 0.021). The haplotype (GGT) consisting of all three risk alleles was significantly overrepresented (87.5%) in patients with PEX.

CONCLUSION

Single nucleotide polymorphisms in LOXL1 are associated with PEX in Polish population which confirms the association previously reported for Icelandic, Swedish, Indian and other populations.

Analysis of LOXL1 polymorphisms in a Saudi Arabian population with pseudoexfoliation glaucoma

PURPOSE

To investigate whether single nucleotide polymorphisms (SNPs) in the lysyl oxidase-like 1 (LOXL1) gene are associated with pseudoexfoliation glaucoma (PEG) in the Saudi Arabian population.

METHODS

The coding regions of LOXL1 were fully sequenced in 93 clinically diagnosed PEG patients and 101 healthy controls. Both groups were Saudi Arabs. Previously reported and newly identified SNPs were evaluated for possible association with PEG and their pathological consequences on the gene were assessed.

RESULTS

The "G" allele frequencies of both rs1048661 and rs3825942 SNPs differed between PEG patients and control subjects from Saudi Arabia (p=0.0056 and p=0.000005, respectively). This significance remained after applying the Bonferroni correction. Two non-synonymous novel SNPs in LOXL1 were detected in the PEG patients and not in the controls. One of these SNPs was in exon 4 (g.25722 C>G; codon change D484E) of LOXL1 and was predicted to be non-pathological; the other was in exon 6 of LOXL1 (g.28084 T>G; codon change Y559D) and was predicted to be probably damaging. All alleles of SNPs (rs28706550, rs35203737, rs41429348, rs12906373, rs41435250, and rs13329473) were monoallelic in this population. No allele frequency difference for rs8818 and rs3522 SNP between patients and controls (p values were 0.126 and 0.994 respectively).

CONCLUSIONS

Similar to almost all non-African populations tested thus far, the "G" allele of both rs1048661 and rs3825942 SNPs were associated with the risk of PEG in the Saudi Arab population.

Lack of association of polymorphisms in elastin with pseudoexfoliation syndrome and glaucoma

PURPOSE

To evaluate the elastin gene (ELN) as a secondary risk factor for pseudoexfoliation syndrome (PXFS) and the associated glaucoma pseudoexfoliation glaucoma (PXFG).

METHODS

One hundred seventy-eight unrelated patients with PXFS, including 132 patients with PXFG, and 113 unrelated controls were recruited from the Massachusetts Eye and Ear Infirmary. All the patients and controls were white of European ancestry. Three tag SNPs (rs2071307, rs3823879, and rs3757587) that capture the majority of alleles in ELN were genotyped. Single-SNP association was analyzed using Fisher exact test. Haplotype analysis and the set-based test were used to assess the association for the whole gene. Interaction analysis was done between the ELN SNP rs2071307 and LOXL1 SNP rs2165241 using logistic regression. Multiple comparisons were corrected using the Bonferroni method.

RESULTS

All 3 ELN tag SNPs were not significantly associated with PXFS and PXFG (P>0.20). The minor allele frequencies in PXFS, PXFG, and controls were 40.7%, 39.8%, and 45.6%, respectively for rs2071307, 6.7%, 6.3%, and 5.4% for rs3823879, and 14.8%, 16.2%, and 13.6% for rs3757587. Haplotype analysis and the set-based test did not find significant association of ELN with PXFS (P=0.94 and 0.99, respectively). No significant interaction effects on PXFS were identified between the ELN and LOXL1 SNPs (P=0.55).

CONCLUSIONS

Our results suggest that common polymorphisms of ELN are not associated with PXFS and PXFG in white populations. Further studies are required to identify secondary genetic factors that contribute to PXFS.

LOXL1 expression in lens capsule tissue specimens from individuals with pseudoexfoliation syndrome and glaucoma

PURPOSE

To study lysyl oxidase-like 1 (LOXL1) expression in freshly collected lens capsules from pseudoexfoliation syndrome (XFS), pseudoexfoliation glaucoma (XFG), and normal cataract control individuals. We also investigated the effects of four glaucoma drug medications on LOXL1 expression in primary human lens epithelial cell cultures to see if they could affect LOXL1 expression.

METHODS

Lens capsules were collected at the time of cataract surgery. Controls were matched to age, sex, and ethnicity. Total RNA was isolated from individual lens capsule samples and real-time PCR was performed on each sample using primers flanking the sixth exon of the LOXL1 gene. Cell cultures were grown to confluence in four separate six-well plates at 37 °C in 5% CO2. Each plate was then treated with one of four different glaucoma drugs (brinzolamide 1%, brimonidine tartrate 0.1%, timolol maleate 0.5%, and latanoprost 0.005%) once daily for seven days (at both 1:1,000 and 1:100 concentrations relative to media). Controls were not treated with any drug but media was changed in the same manner. After one week of treatment, cells were harvested and total RNA isolated. Real-time PCR was performed on each group of cells.

RESULTS

Seven XFS, seven XFG, and ten cataract control specimens were analyzed. LOXL1 expression was detected in the lens capsule specimens from each of the four groups. Significant expression differences were found between the control and XFG groups and XFS and XFG groups. No significant difference was observed between the control and XFS group. No significant decrease in LOXL1 expression was seen with drug incubation of the four medications (Brinzolamide, Timolol, Latanoprost, and Brimonidine) at the 1:1,000 drug:media concentrations versus controls. At 10-fold higher concentrations (1:100 drug:media), brinzolamide, timolol maleate, and latanoprost showed small increases in LOXL1 expression relative to controls. This effect was not observed with brimonidine tartrate.

CONCLUSIONS

These results establish that LOXL1 expression is reduced in lens capsule specimens from XFG individuals but not XFS. The drug treatment incubation studies suggest that the change in LOXL1 expression observed in XFG is not attributable to glaucoma drug therapy. If a causative functional relationship can be validated, modification of LOXL1 expression in affected tissues may represent a novel treatment strategy for this disorder.

Glaucoma: genes, phenotypes, and new directions for therapy

Glaucoma, a leading cause of blindness worldwide, is characterized by progressive optic nerve damage, usually associated with intraocular pressure. Although the clinical progression of the disease is well defined, the molecular events responsible for glaucoma are currently poorly understood and current therapeutic strategies are not curative. This review summarizes the human genetics and genomic approaches that have shed light on the complex inheritance of glaucoma genes and the potential for gene-based and cellular therapies that this research makes possible.

Genome-wide association study with DNA pooling identifies variants at CNTNAP2 associated with pseudoexfoliation syndrome

Genetic and nongenetic factors contribute to development of pseudoexfoliation (PEX) syndrome, a complex, age-related, generalized matrix process frequently associated with glaucoma. To identify specific genetic variants underlying its etiology, we performed a genome-wide association study (GWAS) using a DNA-pooling approach. Therefore, equimolar amounts of DNA samples of 80 subjects with PEX syndrome, 80 with PEX glaucoma (PEXG) and 80 controls were combined into separate pools and hybridized to 500K SNP arrays (Affymetrix). Array probe intensity data were analyzed and visualized with expressly developed software tools GPFrontend and GPGraphics in combination with GenePool software. For replication, independent German cohorts of 610 unrelated patients with PEX/PEXG and 364 controls as well as Italian cohorts of 249 patients and 190 controls were used. Of 19, 17 SNPs showing significant allele frequency difference in DNA pools were confirmed by individual genotyping. Further single genotyping at CNTNAP2 locus revealed association between PEX/PEXG for two SNPs, which was confirmed in an independent German but not the Italian cohort. Both SNPs remained significant in the combined German cohorts even after Bonferroni correction (rs2107856: P(c)=0.0108, rs2141388: P(c)=0.0072). CNTNAP2 was found to be ubiquitously expressed in all human ocular tissues, particularly in retina, and localized to cell membranes of epithelial, endothelial, smooth muscle, glial and neuronal cells. Confirming efficiency of GWAS with DNA-pooling approach by detection of the known LOXL1 locus, our study data show evidence for association of CNTNAP2 with PEX syndrome and PEXG in German patients.

Role of functional single nucleotide polymorphisms of MMP1, MMP2, and MMP9 in open angle glaucomas

PURPOSE

Matrix metalloproteinases (MMPs) play an essential role in the turnover of the extracellular matrix and cellular behavior. MMP1, MMP2, and MMP9 have previously been implicated in the pathogenesis of primary open angle glaucoma (POAG) and open angle glaucoma secondary to exfoliation syndrome (XFG), respectively. Functional gene polymorphisms of these MMPs such as MMP1 -1607 1G/2G (rs1799750), MMP2 -1306 C/T (rs243865), MMP2 -1575 G/A (rs243866), and MMP9 Q279R (rs17576) are thus plausible candidates as risk factors for open angle glaucomas. The purpose of the present study was to investigate hypothesized associations between these polymorphisms and the presence of POAG and XFG in a Caucasian population.

METHODS

The present case-control study included 322 patients with POAG, 202 patients with XFG, and 248 control subjects. Genotyping of polymorphisms was done using polymerase chain reaction.

RESULTS

No significant differences in either genotype distributions or allelic frequencies of MMP1 -1607 1G/2G, MMP2 -1306 C/T, MMP2 -1575 G/A, and MMP9 Q279R were found between patients with POAG and control subjects and patients with XFG and control subjects, respectively (p>0.05). The presence of POAG or XFG was not predicted by any of the investigated polymorphisms.

CONCLUSIONS

Our data suggest that the MMP1 -1607 1G/2G, MMP2 -1306 C/T, MMP2 -1575 G/A, and MMP9 Q279R polymorphisms themselves are unlikely major risk factors among Caucasian patients with either POAG or XFG.

Lysyl oxidase-like 1 gene polymorphisms in German patients with normal tension glaucoma, pigmentary glaucoma and exfoliation glaucoma

PURPOSE

To evaluate the association between lysyl-oxidase-like 1 (LOXL1) gene polymorphisms and exfoliation glaucoma, pigmentary glaucoma and normal tension glaucoma in a case-control cohort of German patients.

METHODS

Six single nucleotide polymorphisms in a 22 kb genomic region encompassing the LOXL1 gene plus an additional "outlier" single nucleotide polymorphism located approximately 1.1 Mb upstream of LOXL1 were genotyped in 128 exfoliation glaucoma patients, 88 pigmentary glaucoma patients, 273 normal tension glaucoma patients, and 280 healthy control subjects either with TaqMan allelic discrimination assays or by direct sequencing, and a genetic association study was performed.

RESULTS

For the exfoliation glaucoma cases, case-control allelic association for 6 single nucleotide polymorphisms were highly significant. In contrast, there were no genotypic differences between pigmentary glaucoma cases, normal tension glaucoma cases and controls. However, an association between rs1048661 genotype and age at disease onset was suggested for pigmentary glaucoma patients.

CONCLUSIONS

Our study reveals that in the German population the LOXL1 genetic predisposition is limited to exfoliation glaucoma and does not include normal tension glaucoma. In addition, our study implicates that LOXL1 polymorphisms are not likely to have a major influence on the pathophysiology of pigmentary glaucoma. However, 1 nonsynonymous polymorphism may serve as a predictor of age at disease onset in pigmentary glaucoma.

Whole genome association studies in complex diseases: where do we stand?

Hundreds of genome-wide association studies have been performed in recent years in order to try to identify common variants that associate with complex disease. These have met with varying success. Some of the strongest effects of common variants have been found in lateonset diseases and in drug response. The major histocompatibility complex has also shown very strong association with a variety of disorders. Although there have been some notable success stories in neuropsychiatric genetics, on the whole, common variation has explained little of the high heritability of these traits. In contrast, early studies of rare copy number variants have led rapidly to a number of genes and loci that strongly associate with neuropsychiatric disorders. It is likely that the use of whole-genome sequencing to extend the study of rare variation in neuropsychiatry will greatly advance our understanding of neuropsychiatric genetics.

Major LOXL1 risk allele is reversed in exfoliation glaucoma in a black South African population

PURPOSE

To investigate whether variants in the lysyl oxidase-like 1 (LOXL1) gene are associated with exfoliation glaucoma (XFG) and primary open-angle glaucoma (POAG) in an ancestral population from South Africa.

METHODS

Black South African subjects with XFG, POAG, and age matched unaffected controls were recruited from the St. John Eye Hospital in Soweto, Johannesburg, South Africa, using standard clinical examination techniques. Fifty individuals were collected for each of the three groups: XFG, POAG, and normal controls. The complete coding region of LOXL1 was sequenced using the PCR-based Sanger method. The allele frequencies of the identified sequence variants were compared between XFG or POAG and controls using Fisher's exact test.

RESULTS

A large number of coding variants were identified, including rs1048661 (R141L), rs3825942 (G153D), S159A, S161L, rs41435250 (A320A), rs13329473 (F489F), and T567A. The allele frequencies of both rs3825942 and rs1048661 differed significantly between the XFG and control subjects from South Africa (p=5.2 x 10(-13) and 1.7 x 10(-5), respectively). The G allele for rs1048661 (encoding arginine) was the risk allele which is similar to other populations. The A allele of rs3825942 (encoding aspartic acid) was the risk allele, in sharp contrast to the G allele (encoding glycine) reported in multiple other populations. There was no significant difference in the allele frequencies of coding variants in LOXL1 between POAG and control subjects.

CONCLUSIONS

This represents the first genetic association study of LOXL1 in an ancestral African population with XFG. We have confirmed the association between variants of LOXL1 and XFG. To date, the G allele of the major susceptibility variant rs3825942 has consistently been shown in multiple populations to increase the risk of XFG. Surprisingly, we have found a strong association with the opposite allele in the South African population. This suggests that other as yet unknown causal variants of LOXL1 contribute to the genetic risk of XFG.

Ethnicity-based subgroup meta-analysis of the association of LOXL1 polymorphisms with glaucoma

PURPOSE

To investigate the association and ethnic heterogeneity of lysyl oxidase-like 1 (LOXL1) single nucleotide polymorphisms (SNPs) with exfoliation syndrome (XFS)/exfoliation glaucoma (XFG) and other types of glaucoma.

METHODS

We performed meta-analysis and ethnicity-based subgroup analyses according to published studies. Allele and genotype frequencies of SNPs rs1048661, rs2165241, and rs3825942 were extracted for analysis in Reviewer Manager: (1) comparison of the allelic distributions between XFS and XFG, (2) allelic association of LOXL1 SNPs with XFS/XFG, (3) associations in homozygote, heterozygote, and dominant and recessive models, and (4) allelic association with primary open angle glaucoma (POAG).

RESULTS

In total 24 reported articles were retrieved, including Caucasian, African, Japanese, Indian, and Chinese populations. There was no significant difference in the distributions of rs1048661, rs2165241, and rs3825942 between XFS and XFG. The G allele of rs3825942 was the common at-risk allele for XFS/XFG in all populations with a total odds ratio (OR) of 10.89. The total homozygote OR of rs3825942 was 9.06 for XFS/XFG combined, but the total heterozygote OR was not significant. We also found that in the recessive model, the total OR was 14.70. There was no association of the three SNPs with POAG.

CONCLUSIONS

The association of rs3825942, but not rs2165241 or rs1048661, with XFS/XFG is consistent in different ethnic populations in the recessive model. LOXL1 is not associated with POAG in all study populations.

Evaluation of LOXL1 polymorphisms in exfoliation syndrome in a Chinese population

PURPOSE

To evaluate the association profiles of the lysyl oxidase-like 1 (LOXL1) gene polymorphisms with exfoliation syndrome in a Chinese population.

METHODS

Fifty unrelated patients with exfoliation syndrome and 125 control subjects were included. Genotypes of the three single nucleotide polymorphisms (SNPs) of LOXL1 (rs1048661, rs3825942, and rs2165241) were analyzed by direct sequencing, and a case-control association study was performed.

RESULTS

The three SNPs were significantly associated with exfoliation syndrome (XFS) and exfoliation glaucoma (XFG) individually. After controlling for rs3825942 and rs2165241, the association between rs1048661 and XFS/XFG remained significant (p=3.6 x 10(-7)). At this SNP, the T allele and TT genotype conferred a 7.59-(95% confidence interval [CI]: 3.87-14.89, p=6.95 x 10(-11)) and 8.69-(95% CI: 4.15-18.20, p<1.00 x 10(-7)) fold increased risk to the disease. The alleles of T at rs1048661 and C at rs2165241 were found to be risk alleles in Chinese subjects, which were opposite to Caucasian individuals. The haplotypes T-G, defined by SNPs rs1048661 and rs3825942, and T-C by SNPs rs1048661 and rs2165241, were also significantly associated with the disorder. However when the genotypic or allelic frequencies of the three SNPs were compared between XFS and XFG, no significant difference was detected.

CONCLUSIONS

LOXL1 is a susceptibility gene of XFS/XFG in the Chinese population, and the association is mainly attributed to SNP rs1048661. The risk alleles of rs1048661 and rs2165241 in Chinese subjects were found to be opposite to that of Caucasians. The genotypic and allelic distributions of these SNPs are similar between XFS and XFG.

From epidemiology to lysyl oxidase like one (LOXL1) polymorphisms discovery: phenotyping and genotyping exfoliation syndrome and exfoliation glaucoma in Iceland

The first Icelandic articles on exfoliation syndrome (XFS) and exfoliation glaucoma (XFG) appeared some 35 years ago in 1974. Articles since then have included epidemiology, pedigree-based and twin-studies as well as investigations into XFG response to medical therapy and XFS/XFG genetics. All studies found XFS/XFG to be common in Iceland and to be age-related. The Reykjavik Eye Study (RES), a population-based epidemiological study, was first conducted in 1996. The RES found that XFS and XFG prevalence in patients aged 50 years and older was 11% and that XFS/XFG was more common in women than in men. These results were confirmed in 5- and 12-year incidence studies that also suggested that detailed characterization of the phenotype is important, including pupil dilation. In the RES, eyes with XFS were found to be clinically unilateral in about half of cases and to have higher mean intraocular pressure (IOP) than non-XFS eyes. However, XFS was not found to be associated with central corneal thickness, corneal curvature, anterior chamber depth, lens thickness, lens opacification or optic disc morphology. About 15% of persons with XFS had XFG, and XFG eyes had higher risk of developing visual impairment and blindness than eyes with primary open-angle glaucoma. The first genetic studies on Icelanders, conducted about 12 years ago, were linkage studies and were unsuccessful in discovering the genetics behind XFS/XFG. However, in 2007 a genome-wide association study in Iceland using more than 300 000 markers [single nucleotide polymorphisms (SNPs)] on a relatively small number of patients did discover that lysyl oxidase like 1 (LOXL1) on chromosome 15q24 is a major gene for XFS/XFG. These results have now largely been replicated world-wide.

Three susceptible loci associated with primary open-angle glaucoma identified by genome-wide association study in a Japanese population

Primary open-angle glaucoma (POAG) is the major type of glaucoma. To discover genetic markers associated with POAG, we examined a total of 1,575 Japanese subjects in a genome-wide association study (stage 1) and a subsequent study (stage 2). Both studies were carried out at a single institution. In the stage 1 association study, we compared SNPs between 418 POAG patients and 300 control subjects. First, low-quality data were eliminated by a stringent filter, and 331,838 autosomal SNPs were selected for analysis. Poorly clustered SNPs were eliminated by a visual assessment, leaving 255 that showed a significant deviation (P < 0.001) in the allele frequency comparison. In the stage 2 analysis, we tested these 255 SNPs for association in DNA samples from a separate group of 409 POAG and 448 control subjects. High-quality genotype data were selected and used to calculate the combined P values of stages 1 and 2 by the Mantel-Haenszel test. These analyses yielded 6 SNPs with P < 0.0001. All 6 SNPs showed a significant association (P < 0.05) in stage 2, demonstrating a confirmed association with POAG. Although we could not link the SNPs to the annotated gene(s), it turned out that we have identified 3 genetic loci probably associated with POAG. These findings would provide the foundation for future studies to build on, such as for the metaanalysis, to reveal the molecular mechanism of the POAG pathogenesis.

Genetics of pseudoexfoliation syndrome

PURPOSE OF REVIEW

Pseudoexfoliation syndrome (XFS) is a late-onset and complex disorder that is strongly associated with the development of glaucoma. The purpose of this review is to discuss the inheritance patterns and recent genetic advances in the study of this disorder.

RECENT FINDINGS

XFS has a strong familial association and recently, the lysyl oxidase-like 1 gene has been strongly associated with this disorder. This gene is involved in the synthesis and maintenance of elastic fibers and therefore has a strong biological rationale for being involved in this disorder. However, the exact relationship between lysyl oxidase-like 1 polymorphisms and the development of XFS has not been elucidated. Also, the value of genetic testing for this disorder has not been validated.

SUMMARY

XFS is an important risk factor for glaucoma and lysyl oxidase-like 1 polymorphisms are strongly associated with XFS. The mechanisms behind glaucoma development and the value of genetic testing are not clear and further study is needed.

Association of LOXL1 gene with Finnish exfoliation syndrome patients

In this study, three single-nucleotide polymorphisms (SNPs) on the lysyl oxidase-like 1 (LOXL1) gene associated with exfoliation syndrome (XFS) and exfoliation glaucoma (XFG) were investigated in the Finnish population. A case-control study of 59 sporadic patients with XFS, 82 with XFG, 71 with primary open-angle glaucoma (POAG) and 26 individuals without these disorders from the southern Finnish population, and a family study of an extended family with 28 patients with XFS or XFG and 92 unaffected relatives from Kökar islands, Southwestern Finnish archipelago, were conducted. Anonymous blood donors (n=404) were studied as population-based controls. Three SNPs, rs1048661 (R141L), rs3825942 (G153D) and rs2165241, of the LOXL1 gene were genotyped by PCR sequencing. Association and linkage analyses were carried out. In both case-control and family materials, significant association for allele G of rs1048661 (P=2.65 x 10(-5); P=0.0007), allele G of rs3825942 (P=2.24 x 10(-8); P=0.49) and allele T of rs2165241 (P=2.62 x 10(-13); P<0.0001) was found in XFS/XFG. However, linkage was not observed for LOXL1 risk alleles. The corresponding three-locus haplotype GGT increased the risk of XFS/ XFG nearly 15-fold relative to low-risk haplotype GAC (odds ratio (OR): 14.9, P=1.6 x 10(-16)). In conclusion, the earlier reported polymorphisms of the LOXL1 gene showed significant association also in the Finnish population.

Different WDR36 mutation pattern in Chinese patients with primary open-angle glaucoma

PURPOSE

To determine the distribution of WD repeat domain 36 (WDR36) sequence variants in Chinese patients with primary open-angle glaucoma (POAG).

METHODS

One hundred and thirty-five unrelated POAG patients (82 high tension glaucoma [HTG], 42 normal tension glaucoma [NTG], and 11 juvenile-onset POAG [JOAG] patients) and 77 unrelated controls were recruited. All 23 coding exons and splicing junctions of WDR36 were sequenced using BigDye Terminator v3.1 cycle sequencing kit. Single nucleotide polymorphism (SNP) and haplotype associations were analyzed using PLINK (version 1.04).

RESULTS

Nineteen sequence alterations were identified, and eight of them were novel including two novel nonsynonymous SNPs (L240V and I713V). Except the common I264V polymorphism, no other previously reported disease-causing or disease-susceptibility mutations were found. The novel I713V mutation was observed in three (3.7%) patients with HTG. One intronic SNP, IVS5+30C>T (rs10038177), showed significantly higher frequency of minor allele T in HTG patients (16.5%) than in controls (1.3%; Odds ratio [OR]=15.0, p=7.9 x 10(-7), Bonferroni corrected p=1.5 x 10(-5)). Haplotype GTA, which is composed of rs13153937, rs10038177, and rs11241095, was significantly associated with HTG (OR=22.5, p=0.002, Bonferroni corrected p=0.013). Neither the individual SNPs nor haplotypes of WDR36 were associated with NTG or JOAG (Bonferroni corrected p>0.05).

CONCLUSIONS

Findings in this study suggest WDR36 to be associated with sporadic HTG but not with NTG or JOAG. Our results also suggest a different mutation pattern of WDR36 in the Chinese population from other ethnic populations.

TNF-alpha -308 G>A and -238 G>A polymorphisms are not major risk factors in Caucasian patients with exfoliation glaucoma

PURPOSE

TNF-alpha has been suggested to participate in the pathogenesis of exfoliation glaucoma (XFG). The purpose of the present study was to investigate a hypothesized association between two common functional polymorphisms in the promoter region of the TNF-alpha gene (TNF-alpha -308 G>A, rs1800629, and TNF-alpha -238 G>A, rs361525) and the presence of XFG in a Caucasian population.

METHODS

The present case-control study comprised 408 participants (204 patients with XFG and 204 control subjects). Control subjects were matched for age and sex. Genotypes of the TNF-alpha -308 G>A and TNF-alpha -238 G>A polymorphisms were determined by polymerase chain reaction (restriction fragment length polymorphism).

RESULTS

No significant differences regarding genotype distribution or allelic frequencies were found between patients and control subjects (p>0.025). The presence of the TNF-alpha -308 G-allele was associated with an insignificant odds ratio of 0.98 (95% confidence interval [CI]: 0.66-1.46; p=0.99) while the presence of the TNF-alpha -238 G-allele was associated with an insignificant odds ratio of 0.64 (95% CI: 0.33-1.23; p=0.25).

CONCLUSIONS

Our data suggest that both the TNF-alpha -308 G>A and the TNF-alpha -238 G>A polymorphisms are unlikely to be major risk factors for XFG in an European population of Caucasian descent.

Lack of association of polymorphisms in homocysteine metabolism genes with pseudoexfoliation syndrome and glaucoma

PURPOSE

To evaluate genes involved in homocysteine metabolism as secondary risk factors for pseudoexfoliation syndrome (PXFS) and the associated glaucoma (PXFG).

METHODS

One hundred eighty-six unrelated patients with PXFS, including 140 patients with PXFG and 127 unrelated control subjects were recruited from the Massachusetts Eye and Ear Infirmary. All the patients and controls were Caucasian of European ancestry. Seventeen tag SNPs from 5 genes (methylenetetrahydrofolate reductase [MTHFR], methionine synthase [MTR], methionine synthase reductase [MTRR], methylenetetrahydrofolate dehydrogenase [MTHFD1], and cystathionine beta-synthase [CBS]) were genotyped. Single-SNP association was analyzed using Fisher's exact test (unconditional) or logistic regression after conditioning on the effects of age and three LOXL1 SNPs (rs1048661, rs3825942, and rs2165241). Interaction analysis was performed between the homocysteine and LOXL1 SNPs using logistic regression. Haplotype analysis and the set-based test were used to test for association of individual genes. Multiple comparisons were corrected using the Bonferroni method.

RESULTS

One SNP (rs8006686) in MTHFD1 showed a nominally significant association with PXFG (p=0.015, OR=2.23). None of the seventeen SNPs tested were significantly associated with PXFS or PXFG after correcting for multiple comparisons (Bonferroni corrected p>0.25). After controlling for the effects of age and three associated LOXL1 SNPs, none of the seventeen tested SNPs were associated with PXFS (p>0.12). No significant interaction effects on PXFS were identified between the homocysteine and LOXL1 SNPs (p>0.06). Haplotype analysis and the set-based test did not find significant association of individual genes with PXFS (p>0.23 and 0.20, respectively).

CONCLUSIONS

Five genes that are critical components of the homocysteine metabolism pathway were evaluated as secondary factors for PXFS and PXFG. Our results suggest that these genes are not significant risk factors for the development of these conditions.

Lyst mutation in mice recapitulates iris defects of human exfoliation syndrome

PURPOSE

Human eyes with exfoliation syndrome (XFS) exhibit a distinctive pattern of iris transillumination defects that are recapitulated in Lyst mutant mice carrying the beige allele. The purpose of this study was to determine the anatomic basis for Lyst-mediated transillumination defects, test whether Lyst mutant mice develop other features of XFS, and describe the molecular basis of the beige mutation.

METHODS

Lyst mutant mice and strain-matched controls were compared by clinical, histologic, immunohistochemical, and molecular genetic analyses.

RESULTS

Slit-lamp examination showed that Lyst mutant mice uniformly exhibit XFS-like transillumination defects. Histologic analysis showed that these defects correlate with a sawtooth morphology of the iris pigment epithelium. Lyst mutant mice also produce an exfoliative-like material and exhibit pronounced pigment dispersion. Despite these insults, Lyst mutation does not cause increased intraocular pressure or optic nerve damage in the C57BL/6J genetic background. Sequence analysis identified that the beige mutation is predicted to delete a single isoleucine from the WD40 domain of the LYST protein, suggesting that this mutation is likely to disrupt a protein-protein interaction.

CONCLUSIONS

Lyst mutant eyes exhibit multiple features of XFS. Recent human genetic association studies have identified changes occurring in the LOXL1 gene as an important risk factor for XFS but also indicated that other factors contributing to risk likely exist. These results demonstrated that mutation of the Lyst gene can produce ocular features of human XFS and suggested that LYST or LYST-interacting genes may contribute to XFS.

Genotype-correlated expression of lysyl oxidase-like 1 in ocular tissues of patients with pseudoexfoliation syndrome/glaucoma and normal patients

Pseudoexfoliation (PEX) syndrome is a generalized disease of the extracellular matrix and the most common identifiable cause of open-angle glaucoma. Two single nucleotide polymorphisms in the lysyl oxidase-like 1 (LOXL1) gene (rs1048661 and rs3825942) have been recently identified as strong genetic risk factors for both PEX syndrome and PEX glaucoma. Here we investigated the expression and localization of LOXL1, LOXL2, and lysyl oxidase (LOX) in tissues of PEX syndrome/glaucoma patients and controls in correlation with their individual single nucleotide polymorphism genotypes and stages of disease. LOXL1 ocular expression was reduced by approximately 20% per risk allele of rs1048661, whereas risk alleles of rs3825942, which were highly overrepresented in PEX cases, did not affect LOXL1 expression levels. Irrespective of the individual genotype, LOXL1 expression was significantly increased in early PEX stages but was decreased in advanced stages both with and without glaucoma compared with controls, whereas LOX and LOXL2 showed no differences between groups. LOXL1 was also found to be a major component of fibrillar PEX aggregates in both intra- and extraocular locations and to co-localize with various elastic fiber components. These findings provide evidence for LOXL1 involvement in the initial stages of abnormal fibrogenesis in PEX tissues. Alterations of LOXL1 activation, processing, and/or substrate specificity may contribute to the abnormal aggregation of elastic fiber components into characteristic PEX fibrils.

LOXL1 variants in elderly Japanese patients with exfoliation syndrome/glaucoma, primary open-angle glaucoma, normal tension glaucoma, and cataract

PURPOSE

To evaluate the association of lysyl oxidase like 1 (LOXL1) gene variants in Japanese patients with open-angle glaucoma.

METHODS

We evaluated the association of three LOXL1 variants (rs1048661, rs3825942, and rs2165241) in 142 Japanese patients with exfoliation syndrome (EX; n=59) and exfoliation glaucoma (EG; n=83) as well as in 251 control patients aged 70 years or older with primary open-angle glaucoma (PG; n=40), normal tension glaucoma (NG; n=54), and cataract (CT; n=157).

RESULTS

In comparison with the CT group, the single nucleotide polymorphisms (SNPs) showed significant association with EX, EG, and EX+EG. The odds ratio (OR)=19.71-28.23 and p=1.69 x 10(-23) - 3.00 x 10(-45) for allele T of rs1048661; OR=28.21-39.78 and p=1.77 x 10(-8) - 2.42 x 10(-22) for allele G of rs3825942; and OR=16.59-23.40 and p=4.79 x 10(-5) - 1.08 x 10(-9) for allele C of rs2165241. In comparison with the controls (CT+PG+NG), the haplotype rs1048661/rs3825942 (T/G) was significantly associated with EX+EG (p=8.27 x 10(-44)), and haplotype G/A had a significant protective effect (p=2.25 x 10(-14)). None of the three SNPs showed significant differences between the EX and EG groups or between the PG and NG groups.

CONCLUSIONS

These SNPs are associated with exfoliation syndrome/glaucoma in the Japanese population. The risk alleles in rs1048661 and rs2165241 are different from other populations. Additional genetic or environmental risk factors other than these LOXL1 SNPs could be associated with the development of exfoliation syndrome as well as exfoliation glaucoma among exfoliation syndrome patients.

Molecular pathology of pseudoexfoliation syndrome/glaucoma--new insights from LOXL1 gene associations

Pseudoexfoliation (PEX) syndrome is a generalized disease of the extracellular matrix and a major cause of severe open-angle glaucoma. Single nucleotide polymorphisms (SNPs) in exon 1 of the lysyl oxidase-like 1 (LOXL1) gene have been recently identified as strong genetic risk factors for both PEX syndrome and PEX glaucoma. LOXL1 is a pivotal cross-linking enzyme in extracellular matrix metabolism and seems to be specifically required for elastic fiber formation and stabilization. This review outlines our current understanding of the role of LOXL1 in the pathophysiology of PEX syndrome and PEX glaucoma. The available data suggest that LOXL1 is differentially regulated dependent on the phase of progression of the fibrotic process. While increased levels of LOXL1 participate in the formation of abnormal PEX fiber aggregates in the initial phase of fibrogenesis, inadequate tissue levels may promote elastotic processes in advanced stages of the disease. Although the functional significance of LOXL1 in the specific PEX-associated matrix process still has to be determined, elucidation of the underlying molecular pathogenesis has been evolving, and might eventually open new approaches for specific treatment strategies in the future.

Evaluation of LOXL1 polymorphisms in eyes with exfoliation glaucoma in Japanese

PURPOSE

To investigate the lysyl oxidase-like 1 (LOXL1) gene for single nucleotide polymorphism (SNP) variations in Japanese patients with exfoliation syndrome (XFS) and exfoliation glaucoma (XFG) and to examine the phenotypes of the patients with these variations.

METHODS

Fifty-six unrelated Japanese patients with XFS, including 36 patients with XFG, were studied. Genomic DNA was extracted from the leukocytes of peripheral blood, and three SNPs (rs1048661; p.Arg141Leu, rs3825942; p.Gly153Asp, and rs2165241) were identified. These SNPs were amplified by polymerase chain reaction (PCR), directly sequenced, and genotyped.

RESULTS

Two nonsynonymous variants in exon 1 of LOXL1,rs1048661 and rs3825942, were found to be strongly associated with XFS including XFG. The frequency of the T allele (0.964) in rs1048661 in eyes with XFS was much higher in controls (0.507) with a p value of 7.7x10(-18). The odds ratio for the T allele in rs1048661 was 26.0 (95% confidence interval, 18.3-37.1). In the haplotype analysis, T-G was overrepresented in XFS subjects (p=7.7x10(-18)), showing a highly significant difference in frequency between primary open-angle glaucoma (POAG) and the control group (p=0.07), but the G-G and G-A haplotypes were less represented in XFS subjects (p=1.1x10(-11) and p=1.0x10(-4), respectively). However, an earlier study reported the strongest associated SNP with XFS and XFG, rs2165241, showed no association.

CONCLUSIONS

SNPs of LOXL1 (rs1048661; Arg141Leu and rs3825942; Gly153Asp) are highly associated with XFS in the Japanese population. However, unidentified genetic or environmental factors independent of LOXL1 will most likely influence the phenotypic expression of the syndrome.

Lysyl oxidase-like 1 gene polymorphisms in Japanese patients with primary open angle glaucoma and exfoliation syndrome

PURPOSE

To assess whether lysyl oxidase-like 1 (LOXL1) polymorphisms are associated with primary open-angle glaucoma (POAG) and exfoliation syndrome (XFS).

METHODS

Japanese patients with POAG (n=213) or XFS (n=89) and 191 control subjects were analyzed for LOXL1 polymorphisms (rs1048661: 758G/T, Arg141Leu and rs3825942: 794G/A, Gly153Asp). Demographic and clinical features of POAG patients and control subjects were compared in terms of the TT/GG compound genotype of rs1048661 and rs3825942.

RESULTS

There was a significant difference in the genotype frequencies between XFS patients and control subjects (p<0.0001). Frequencies of the T allele of rs1048661 and the G allele of rs3825942 were significantly higher in XFS patients than in control subjects (rs1048661: 99.4% versus 55.0%; rs3825942: 99.4% versus 85.3%; p<0.0001). Except for one who had the TG/AG compound genotype, all XFS patients had the TT/GG compound genotype. An almost 250 fold increase in the risk of XFS (p<0.0001; odds ratio: 252.2; 95% confidence interval: 32.7 to more than 1000) was found in patients with the TT/GG compound genotype compared to those without the genotype. There were no significant differences in the genotype and allele frequencies between POAG patients and control subjects. Furthermore, no significant differences were noted in the demographic and clinical features of POAG patients as well as control subjects with and without the TT/GG high-risk compound genotype.

CONCLUSIONS

LOXL1 polymorphisms were associated with XFS. However, the frequencies of the polymorphisms differed between Japanese and Caucasian XFS patients. These polymorphisms had no influence on the phenotypic features of POAG patients.

Exfoliation syndrome and exfoliation glaucoma-associated LOXL1 variations are not involved in pigment dispersion syndrome and pigmentary glaucoma

PURPOSE

Single nucleotide polymorphisms (SNPs) in the LOXL1 gene have been implicated in exfoliation syndrome (XFS) and exfoliation glaucoma (XFG). We have shown that these SNPs are not associated with the primary glaucomas such as primary open-angle (POAG) glaucoma and primary angle-closure glaucoma (PACG). To further establish the specificity of LOXL1 SNPs for XFS and XFG, we determined whether these SNPs were involved in pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG).

METHODS

Three SNPs of LOXL1 (rs1048661, rs3825942, and rs2165241) were screened in a cohort of 78 unrelated and clinically well characterized glaucoma cases comprising of PG (n=44) and PDS (n=34) patients as well as 108 ethnically matched normal controls of Caucasian origin. The criteria for diagnosis of PDS/PG were Krukenberg spindle, hyperpigmentation of the trabecular meshwork, and wide open angle. Transillumination defects were detected by infrared pupillography, and the presence of a Zentmayer ring was considered as a confirmatory sign. All three SNPs were genotyped in cases and controls by resequencing the genomic region of LOXL1 harboring these variants and were further confirmed by polymerase chain reaction (PCR)-based restriction digestions. Haplotypes were generated from the genotype data, and the linkage disequilibrium (LD) and haplotype analysis were done with Haploview software that uses the expectation maximization (EM) algorithm.

RESULTS

The LOXL1 SNPs showed no significant association with PDS or PG. There was no significant difference in the frequencies of the risk alleles of rs1048661 ('G' allele; p=0.309), rs3825942 ('G' allele' p=0.461), and rs2165241 ('T' allele; p=0.432) between PG/PDS cases and controls. Similarly, there was no involvement of the XFS/XFG-associated haplotypes, 'G-G' (p=0.643; [OR=1.08, 95%CI, 0.59-1.97]) and 'T-G' (p=0.266; [OR=1.35, 95%CI, 0.70-2.60]), with the PDS/PG phenotypes. The risk haplotype 'G-G' was observed in ~55% of the normal controls.

CONCLUSIONS

There was no involvement of the LOXL1 SNPs in patients with PDS and PG. The results further indicate that the associations of these SNPs are specific to XFS/XFG.

Lysyl oxidase-like protein 1 (LOXL1) gene polymorphisms and exfoliation glaucoma in a Central European population

PURPOSE

Exfoliation syndrome (XFS) is characterized by an accumulation of abnormal extracellular material in the anterior part of the eye that frequently leads to increased intraocular pressure and glaucomatous optic neuropathy. Recently, two non-synonymous polymorphisms (rs1048661 G>T and rs3825942 G>A) of lysyl oxidase-like protein 1 (LOXL1), a monoamine oxidase that catalyzes the polymerization of tropoelastin to elastin, were found to be associated with increased risk for XFS and exfoliation glaucoma (XFG). The aim of the present study was to investigate the role of these LOXL1 variants in a Central European cohort of Caucasian patients with XFG.

METHODS

The present case-control study comprised of 167 unrelated patients with XFG and 170 control subjects. Genotyping of the LOXL1 rs1048661 and rs3825942 polymorphisms was done using polymerase chain reaction.

RESULTS

The frequency of allele G of rs1048661 as well as rs3825942 was significantly higher in patients than in controls (rs1048661: 0.841 in patients versus 0.669; p<0.001; rs3825942: 0.994 in patients versus 0.817; p<0.001). Odds ratios of 52.1 (95% confidence interval [CI]: 13.85-195.6) and 14.67 (95% CI: 3.81-56.2), respectively, were calculated for the two high-risk haplotypes GG and TG compared to the haplotype GA.

CONCLUSIONS

Our data confirm the previously reported association between LOXL1 polymorphisms and XFG and extend our knowledge to a Central European population.

Lack of association between LOXL1 variants and primary open-angle glaucoma in three different populations

PURPOSE

Significant association has recently been reported between pseudoexfoliation glaucoma (XFG) and two single-nucleotide polymorphisms (SNPs), rs3825942, and rs1048661, in the lysyl oxidase-like 1 gene (LOXL1). The purpose of this study was to investigate whether XFG-associated variants of LOXL1 play a significant role in primary open-angle glaucoma in the Caucasian, African-American, and Ghanaian (West-African) populations.

METHODS

POAG was defined as the presence of glaucomatous optic nerve damage, associated visual field loss, and elevated intraocular pressure (>22 mm Hg in both eyes). Thirteen tagging SNPs were genotyped by allelic discrimination assays in the Caucasian (279 cases and 227 controls), African-American (193 cases and 97 controls), and Ghanaian (170 cases and 138 controls) populations. Allele and genotype frequencies were compared between the cases and controls from each population.

RESULTS

None of the SNPs associated with XFG in LOXL1 were significantly associated with POAG in these populations. The risk allele frequencies for rs2165241 and rs3825942 were significantly lower in the African-American and Ghanaian populations, compared with Caucasian individuals.

CONCLUSIONS

There was no association between SNPs in the LOXL1 gene and POAG. This is the first analysis of the LOXL1 gene in African-American and West-African populations. LOXL1 gene variants do not appear to play a significant role in the pathogenesis of POAG in populations of either Caucasian or West-African ancestry.

Evaluation of LOXL1 polymorphisms in primary open-angle glaucoma in southern and northern Chinese

PURPOSE

The lysyl oxidase-like protein 1 (LOXL1) gene is strongly associated with exfoliation glaucoma, which is very rare in the Chinese population. The implicated LOXL1 polymorphisms have not been associated with primary open-angle glaucoma (POAG). In this study, we investigated three of the LOXL1 polymorphisms in POAG in a southern Chinese population of Hong Kong and northern Chinese from Beijing.

METHODS

The Hong Kong group included 293 POAG patients and 250 controls, and the Beijing group included 169 POAG patients and 197 controls. LOXL1 single nucleotide polymorphisms (SNPs), rs1048661, rs3825942, and rs2165241, were genotyped by direct DNA sequencing. Individual association was analyzed using the chi(2) test, and haplotype-based association analysis was performed in WHAP.

RESULTS

Each of the candidate SNPs was not statistically associated with POAG in either group (p>0.017, Bonferroni correction). Haplotype-based association analysis had identified a significant omnibus association (Omnibus chi(2)=18.16, p=0.00115) between these SNPs and POAG in the Hong Kong group. A minor haplotype (T-G-T) showed significant statistical association with POAG. It presented in 2.1% of cases and 0.4% of controls, conferring a 5.24 fold of increased risk to the disease (95% CI: 1.17-23.54, P(perm)=0.00108). However, this haplotype was absent in the Beijing group.

CONCLUSIONS

Individual LOXL1 SNPs, rs1048661, rs3825942, and rs2165241, were not associated with POAG in the Chinese population. However, a minor haplotype T-G-T was found to be associated with the disorder in the southern Chinese. The low frequencies of the at-risk alleles at rs1048661 and rs2165241 may be one of the factors that led to the low prevalence of exfoliation syndrome in the general populations of the Chinese.