Apolipoprotein E-promoter single-nucleotide polymorphisms affect the phenotype of primary open-angle glaucoma and demonstrate interaction with the myocilin gene

Exploring the role of apolipoprotein E gene promoter polymorphisms in susceptibility to normal-tension glaucoma in a Korean population

Glaucoma, particularly primary open-angle glaucoma (POAG), poses a significant global health concern. Distinguished by intraocular pressure (IOP), POAG encompasses high-tension glaucoma (HTG) and normal-tension glaucoma (NTG). Apolipoprotein E (APOE) is a multifaceted protein with roles in lipid metabolism, neurobiology, and neurodegenerative diseases. However, controversies persist regarding the impact of APOE single-nucleotide polymorphisms (SNPs) on open-angle glaucoma and NTG. This study aimed to identify APOE-specific SNPs influencing NTG risk. A cohort of 178 patients with NTG recruited from Uijeongbu St. Mary's Hospital and 32,858 individuals from the Korean Genome and Epidemiology Study (KoGES) cohort were included in the analysis. Genotype and haplotype analyses were performed on three promoter SNPs (rs449647, rs769446, and rs405509) and two exonic SNPs (rs429358 and rs7412) located on chromosome 19. Among the five SNPs, rs769446 genotypes exhibited significant differences between cases and controls. The minor allele C of rs769446 emerged as a protective factor against NTG. Furthermore, haplotype analysis of the five SNPs revealed that the A-T-G-T-T haplotype was a statistically significant risk factor for NTG. This study indicated an association between APOE promoter SNPs and NTG in the Korean population. Further studies are required to understand how APOE promoter SNPs contribute to NTG pathogenesis.

Normal-Tension Glaucoma and Potential Clinical Links to Alzheimer's Disease

Glaucoma is a group of optic neuropathies and the world's leading cause of irreversible blindness. Normal-tension glaucoma (NTG) is a subtype of glaucoma that is characterized by a typical pattern of peripheral retinal loss, in which the patient's intraocular pressure (IOP) is considered within the normal range (<21 mmHg). Currently, the only targetable risk factor for glaucoma is lowering IOP, and patients with NTG continue to experience visual field loss after IOP-lowering treatments. This demonstrates the need for a better understanding of the pathogenesis of NTG and underlying mechanisms leading to neurodegeneration. Recent studies have found significant connections between NTG and cerebral manifestations, suggesting NTG as a neurodegenerative disease beyond the eye. Gaining a better understanding of NTG can potentially provide new Alzheimer's Disease diagnostics capabilities. This review identifies the epidemiology, current biomarkers, altered fluid dynamics, and cerebral and ocular manifestations to examine connections and discrepancies between the mechanisms of NTG and Alzheimer's Disease.

Region-resolved multi-omics of the mouse eye

The eye is a complex organ consisting of multiple compartments with unique and specialized properties, and small disturbances in one eye region can result in impaired vision and blindness. Although there have been advancements in ocular research, the hierarchical molecular network in region-wide resolution, indicating the division of labor and crosstalk among different eye regions, is not yet comprehensively illuminated. Here, we present an atlas of region-resolved proteome and lipidome of mouse eye. Multiphoton microscopy-guided laser microdissection combined with in-depth label-free proteomics identifies 13,536 proteins across various mouse eye regions. Further integrative analysis of spectral imaging, label-free proteome, and imaging mass spectrometry of the lipidome and phosphoproteome reveals distinctive molecular features, including proteins and lipids of various anatomical mouse eye regions. These deposited datasets and our open proteome server integrating all information provide a valuable resource for future functional and mechanistic studies of mouse eye and ocular disease.

"Association of APOE gene polymorphisms with primary open angle glaucoma in Brazilian patients"

Background: Primary open-angle glaucoma (POAG) is a multifactorial disease that affects 65.5 million people worldwide. In addition to the genetic variants already established as indicators of greater risk for POAG, the apolipoprotein (APOE) gene has been studied in some populations, with controversial results. The aim of this study is to investigate the frequency of the genetic variants of APOE in the Brazilian population, and to evaluate the association between these polymorphisms and the risk of POAG. Methods: APOE variants (rs429358; rs7412) were genotyped in 402 POAG patients and 401 controls. We evaluated the association between APOE genetic variants and the risk for POAG, as well as the correlation between the requirement of glaucoma surgery and the APOE polymorphisms. Results: Among the three APOE gene isoforms, we found a low frequency of APOE alleles ε2 (7.34%) and ε4 (11.76%), but a high frequency of ε3 (80.88%) in our population. When compared to ε3ε3 reference genotype, ε2 allele-carriers (OR = 1.516; p-value = 0.04) and ε2ε3 genotype (OR = 1.655; p-value = 0.02) were associated with a greater risk for POAG. An additive genetic model confirmed the influence of the ε2 allele in the risk of POAG in this sample of the Brazilian population (OR = 1.502; p-value = 0.04). There was no significant association between the analyzed genotypes and the requirement or number of glaucoma surgeries (p > .05). Conclusion: Brazilian individuals carrying the APOEε2 allele may be at an increased risk for the development of POAG.

Neurodegeneration in Alzheimer's disease and glaucoma: overlaps and missing links

The eye is said to be the window into the brain. Alzheimer’s disease (AD) and glaucoma both being diseases of the elderly, have several epidemiological and histological overlaps in pathogenesis. Both these diseases are neurodegenerative conditions. Over the years, a consensus has developed that both may be two ends of a singular spectrum of diseases. Epidemiological studies have shown that more Alzheimer’s patients may be suffering from glaucoma than general healthy population. Retinal ganglion cell damage is a characteristic of both diseases, along with discovery of amyloid-β and tau protein deposition in the retina and aqueous humor of eye. The latter two proteins are known to be pathognomonic of AD. Other pathways such as the insulin receptor pathway also seem to be affected in both diseases similarly. In spite of these overlaps, there are few missing links which still need more evidence, namely, intraocular pressure mechanisms, cerebrospinal fluid pressure and trans-lamina cribrosa pressure gradients, vascular autoregulation factors, etc. Several factors point towards a common pathogenesis at some level for both diseases and prospective studies are necessary to study the natural course of both diseases.

Comparison of two groups for the apolipoprotein E polymorphisms by using next generation sequencing: The first group with three consecutive abortions and the second group with at most one abortion in three consecutive pregnancies

The importance of apolipoprotein E genotypes and allelic polymorphisms in the etiology of recurrent miscarriage is controversial. We plan to investigate this in a two-group study involving more than a thousand participants. In total, 1046 subjects (802 participants in the first group, 244 participants in the second group) were investigated. Women in the first group had a history of ≥3 consecutive spontaneous miscarriage and women in the second group had at most one miscarriage in three consecutive pregnancies. The participants with the following evidence and symptoms were excluded from both groups; structural uterine abnormality, chrosomal abnormalities and polymorphisms, hormonal imbalance, anti-nuclear antibodies, anti-phospholipid antibodies, lupus anticoagulant and homozygous genotype for FV-Leiden, MTHFR C677T, MTHFR A1298C, prothrombin 20210G>A and plasminogen activator inhibitor 4G/5G polymorphisms. We found similar apolipoprotein E allelic frequencies and genotype distributions in both groups. The frequencies of ε2 alleles were 4.1% in the first group and 2.9% in the second group, whereas those of ε3 alleles were 90.8% and 93% in the first group and the second group, respectively and ε4 alleles were 5.1% in the first group and 4.1% in the second group. The genotypes of Apo E observed in the first and the second group respectively were as follows; ε2/ε3 (7.5% and 5.7%), ε3/ε3 (82.7% and 86.5%), ε3/ε4 (8.7% and 7.4%), ε4/ε4 (0.5% and 0.4%) and ε2/ε4 (0.6% and 0). Our data did not support a possible association between apolipoprotein E genotypes and allelic frequencies, and recurrent miscarriages. We believe that the studies excluding the etiological factors that were previously found to be related with any condition are more valuable in the scope of showing the cause-effect relationship.

Neurosteroids and oxysterols as potential therapeutic agents for glaucoma and Alzheimer's disease

Glaucoma is one of the most frequent causes of visual impairment worldwide and involves selective damage to retinal ganglion cells (RGCs) resulting in degeneration of neural pathways connecting retina to visual cortex. It is of interest that similarities in pathological changes have been described in Alzheimer's disease (AD), the most common cause of progressive memory loss and dementia in older people. Accumulation of amyloid-beta (Abeta) and hyperphosphorylated tau is thought to contribute to apoptotic neuronal death in Alzheimer's disease, and similar changes have been linked to apoptotic RGC death in glaucoma. Both glaucoma and Alzheimer's disease also suffer from a lack of effective treatments prompting a search for novel therapeutic interventions. Neurosteroids (NSs) (including oxysterols) are endogenous molecules synthesized in the nervous system from cholesterol that can modulate glutamate and GABA receptors, the primary mediators of fast excitatory and inhibitory neurotransmission in the brain, respectively. Because changes in the glutamate and GABA neurotransmitter systems contribute to the pathogenesis of AD and glaucoma, NSs are possible therapeutic targets for these disorders. In this review, we present recent evidence supporting pathological links between Alzheimer's disease and glaucoma, and focus on the possible role of NSs in these diseases and how NSs might be developed for therapeutic purposes.

Glaucoma in iran and contributions of studies in iran to the understanding of the etiology of glaucoma

Epidemiologic and genetic/molecular research on glaucoma in Iran started within the past decade. A population-based study on the epidemiology of glaucoma in Yazd, a city in central Iran, revealed that 4.4% of studied individuals were affected with glaucoma: 1.6% with high tension primary open angle glaucoma (POAG), 1.6% with normal tension POAG, and 0.4% each with primary angle closure glaucoma (PACG) and pseudoexfoliation glaucoma (PEXG), and other types of secondary glaucoma. Two notable observations were the relatively high frequency of normal tension glaucoma cases (1.6%) and the large fraction of glaucoma affected individuals (nearly 90%) who were unaware of their condition. The first and most subsequent genetic studies on glaucoma in Iran were focused on primary congenital glaucoma (PCG) showing that cytochrome P450 1B1 (CYP1B1) is the cause of PCG in the majority of Iranian patients, many different CYP1B1 mutations are present among Iranian patients but only four mutations constitute the vast majority, and the origins of most mutations in the Iranians are identical by descent (IBD) with the same mutations in other populations. Furthermore, most of the PCG patients are from the northern and northwestern provinces of Iran. A statistically significant male predominance of PCG was observed only among patients without CYP1B1 mutations. Clinical investigations on family members of PCG patients revealed that CYP1B1 mutations exhibit variable expressivity, but almost complete penetrance. A great number of individuals harboring CYP1B1 mutations become affected with juvenile onset POAG. Screening of JOAG patients showed that an approximately equal fraction of the patients harbor CYP1B1 and (myocilin) MYOC mutations; MYOC is a well-known adult onset glaucoma causing gene. Presence of CYP1B1 mutations in JOAG patients suggests that in some cases, the two conditions may share a common etiology. Further genetic analysis of Iranian PCG patients led to identification of Latent-transforming growth factor beta-binding protein 2 (LTBP2) as a causative gene for both PCG and several diseases which are often accompanied by glaucomatous presentations, such as Weill-Marchesani syndrome 3 (WMS3). The findings on LTBP2 have contributed to recognize the importance of the extracellular matrix in pathways leading to glaucoma.

Analysis of the expression and polymorphism of APOE, HSP, BDNF, and GRIN2B genes associated with the neurodegeneration process in the pathogenesis of primary open angle glaucoma

Glaucoma is characterized by optic neuropathy of the RGC or retinal nerve fiber. The aim of this study was to evaluate a relationship between the neurodegenerative genes' polymorphisms of the APOE (rs449647), BDNF (rs2030324), GRIN2B (rs3764028), and HSP70-1 (rs1043618) and the occurrence risk of POAG and to investigate its effect on allele-specific gene expression. Genomic DNA was extracted from peripheral blood. Analysis of the genes' polymorphisms was performed using PCR-RFLP. The level of mRNA expression was determined by QRT-PCR. We showed a statistically significant association of BDNF and APOE genes' polymorphisms with a risk of POAG occurrence. There was a statistically significant association of the rs2030324 polymorphism with progression of POAG based on cup disc ratio value and rs1043618 polymorphism based on nerve fiber index and rim area. Furthermore, we found that mean HSP70-1 mRNA expression was significantly lower in the case of individuals with the G/G genotype than in the case of minor allele carriers, that is, G/C and C/C. We also found that BDNF and HSP70-1 expression level are associated with the progression of POAG based on rim area value. In conclusion, our results suggest that BDNF, APOE, and HSP70-1 genes might be associated with a risk of POAG occurrence in the Polish population.

Association of MYOC and APOE promoter polymorphisms and primary open-angle glaucoma: a meta-analysis

BACKGROUND

Primary open-angle glaucoma (POAG) is the most common form of glaucoma with a genetic predisposition. The relationship between polymorphisms in MYOC or APOE promoter region and POAG has been addressed in many case-control studies, but the published results were not consistent.

METHODS

A meta-analysis assessing the association between five single nucleotide polymorphisms (SNPs) (in MYOC promoter: rs12035719 and rs2075648; in APOE promoter: rs405509, rs769446 and rs449647) and the risk of POAG was performed based on included studies from literature research. In fixed effect model or random effect model, the Mantel-Haenszel (M-H) pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were used to evaluate the genetic association. Stratification analysis was also conducted to test the association within Asian or Caucasian populations.

RESULTS

Twenty five case-control studies within multiple populations were identified and no publish bias was observed. Significant association was detected between POAG risk and MYOC rs2075648 in Caucasian (GA+AA vs. GG, OR=0.587, 95% CI=0.437-0.788, P < 0.001). For other SNPs and in other ethnic populations, no statistic evidence was detected for significant association between them and the development of POAG.

CONCLUSIONS

This meta-analysis suggested a genetic association between one of MYOC polymorphism (rs2075648) and the risk of POAG only in Caucasian population. The significant heterogeneity for this locus might imply the different POAG genetic basis among different populations.

BDNF and HSP gene polymorphisms and their influence on the progression of primary open-angle glaucoma in a Polish population

INTRODUCTION

Glaucoma is a neurodegenerative disease that is often associated with high intraocular pressure (IOP). One of the effects of elevated IOP is disorder of neurotrophic molecules transport, including brain-derived neurotrophic factor (BDNF) and recruit specific cellular proteins called "heat shock proteins" (HSPs). The aim of this study was to evaluate a relationship between the BDNF and HSP70-1 gene polymorphisms with risk occurrence of primary open-angle glaucoma (POAG).

MATERIAL AND METHODS

The study consisted of 167 patients with POAG (mean age: 73 ±9) and 193 healthy subjects (mean age: 64 ±13). Genomic DNA was extracted from peripheral blood. Analysis of the gene polymorphisms was performed using PCR-RFLP, using the following restriction enzymes: NlaIII (rs6265) and BsrBI (rs1043618). The Heidelberg retinal tomography (HRT) clinical parameters were also analyzed. The odds ratios (ORs) and 95% confidence intervals (CIs) for each genotype and allele were calculated.

RESULTS

Comparison of the distributions of genotypes and alleles of the 196G/A polymorphism of the BDNF gene as well as 190G/C polymorphism of the HSP70-1 gene and analysis of the odds ratio (OR) showed no statistically significant differences between POAG patients and controls (p > 0.05). However, there was a statistically significant association of the 196G/A of BDNF and 190G/C of HSP70-1 gene polymorphisms with progression of POAG depending on values of clinical parameters. 196G/A of BDNF correlated with the parameters GDx and RA (p = 0.03; p = 0.002, respectively), while 190G/C of HSP70-1 correlated with c/d and RA (p = 0.014, p = 0.024, respectively).

CONCLUSIONS

The BDNF 196G/A and HSP70-1 190G/C gene polymorphisms may be related to progression of POAG.

Glaucoma and Alzheimer's disease: Their clinical similarity and future therapeutic strategies for glaucoma

Glaucoma refers to a group of diseases characterized by optic neuropathies that are commonly associated with degeneration of the retinal ganglion cells. Although intraocular pressure (IOP) is the only proven treatable factor, several studies indicate that other factors are involved in the pathogenesis of glaucoma. Since normal tension glaucoma (NTG) is the most common glaucoma at least in Japan and South Korea, development of new therapeutic strategies for glaucoma, besides reduction of IOP, is crucial. The clinical characteristics and mechanisms underlying neuronal degeneration in Alzheimer’s disease, a progressive neurodegenerative disease, are similar to those of glaucoma. Impaired cerebral blood flow (CBF) is common to both these diseases; therefore, improving CBF may be considered a new treatment for glaucoma, especially for NTG. In addition, targeting the formation and aggravation pathway for amyloid-β and administration of apolipoprotein E-containing lipoproteins may be potential strategies for glaucoma treatment.

An updated meta-analysis: apolipoprotein E genotypes and risk of primary open-angle glaucoma

PURPOSE

To study the association of apolipoprotein E (APOE) polymorphisms and primary open-angle glaucoma (POAG).

METHODS

After a systematic literature search, all relevant studies evaluating the association between APOE polymorphisms and POAG were included. All statistical tests were calculated with Stata 11.0.

RESULTS

Twelve independent studies on the APOE gene (1,971 cases, 1,756 controls) and POAG were included. A significant association between the APOE gene and POAG was found in the genetic model of ε4/ε4 versus ε3/ε3 (odds ratio [OR] = 2.09, 95% confidence interval [CI] = 1.12-3.88, p = 0.02). However, no association was detected in the models of ε2/ε2 versus ε3/ε3, ε2/ε3 versus ε3/ε3, ε2/ε4 versus ε3/ε3, ε3/ε4 versus ε3/ε3, allele ε2 versus allele ε3, and allele ε4 versus allele ε3. Subgroup analyses showed that a statistically significant association between the APOE gene and the risk of POAG existed in the genetic model of ε4/ε4 versus ε3/ε3 in Asians (OR = 3.55, 95% CI = 1.06-11.87, p = 0.04). No association was identified between the APOE gene and the risk of POAG in Caucasians.

CONCLUSIONS

The present meta-analysis indicated that the ε4/ε4 genotype is associated with increased risk of POAG in Asians.

Association of apolipoprotein E-219T>G promoter polymorphism with primary open angle glaucoma in Turkish population

AIM

To investigate the association between apolipoprotein E (APOE) -219 T>G promoter polymorphism and primary open angle glaucoma (POAG).

METHODS

Patients and healthy subjects were genotyped with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Genotype/allele frequencies were compared between 122 healthy subjects and in 75 POAG patients using Chi-square test.

RESULTS

Although the frequency of APOE -219 GG genotype was higher in POAG group (13.3%) than in control group (6.6%), this finding was not statistically significant (P=0.09). In glaucoma patients carrying GG genotype, mean linear C/D ratio was higher and progression was more compared to glaucoma patients with GT genotype.

CONCLUSION

APOE -219 T>G polymorphism does not seem to be a risk factor for the presence of glaucoma, but might play a role in deterioration of the disease, which needs further evaluation.

Apolipoprotein E gene ε4ε4 is associated with elevated risk of primary open angle glaucoma in Asians: a meta-analysis

Background

Epidemiological studies have evaluated the association between Apolipoprotein E (APOE) gene ε2/ε3/ε4 polymorphism and glaucoma susceptibility. However, the published data are still inconclusive. The aim of the present study is to evaluate the impact of APOE gene ε2/ε3/ε4 polymorphism on glaucoma risk by using meta-analysis.

Methods

A comprehensive literature search of PubMed, EMBASE, Cochrane, Elsevier Science Direct and CNKI databases was conducted to identify relevant articles, with the last report up to January 5, 2014. Pooled odds ratio (OR) and 95% confidence interval (CI) were used to assess the strength of association by using the fixed or random effect model.

Results

Fifteen separate studies including 2,700 cases and 2,365 controls were included in the meta-analysis. We did not detect a significant association between APOE gene ε2/ε3/ε4 polymorphism and glaucoma in overall population (P > 0.0083). In Asians, we detected an association of the ε4ε4 genotype with elevated risk for glaucoma (OR = 5.22, 95% CI = 1.85-14.68, P = 0.002), mainly for primary open angle glaucoma (OR = 4.98, 95% CI = 1.75-14.20, P = 0.003).

Conclusions

The meta-analysis suggests that APOE gene ε4ε4 may be associated with elevated risk for primary open angle glaucoma in Asians. However, more epidemiologic studies based on larger sample size, case–control design and stratified by ethnicity as well as types of glaucoma are suggested to further clarify the relationship between APOE gene ε2/ε3/ε4 polymorphism and genetic predisposition to glaucoma.

Regulation of intraocular pressure by soluble and membrane guanylate cyclases and their role in glaucoma

Glaucoma is a progressive optic neuropathy characterized by visual field defects that ultimately lead to irreversible blindness (Alward, 2000; Anderson et al., 2006). By the year 2020, an estimated 80 million people will have glaucoma, 11 million of which will be bilaterally blind. Primary open-angle glaucoma (POAG) is the most common type of glaucoma. Elevated intraocular pressure (IOP) is currently the only risk factor amenable to treatment. How IOP is regulated and can be modulated remains a topic of active investigation. Available therapies, mostly geared toward lowering IOP, offer incomplete protection, and POAG often goes undetected until irreparable damage has been done, highlighting the need for novel therapeutic approaches, drug targets, and biomarkers (Heijl et al., 2002; Quigley, 2011). In this review, the role of soluble (nitric oxide (NO)-activated) and membrane-bound, natriuretic peptide (NP)-activated guanylate cyclases that generate the secondary signaling molecule cyclic guanosine monophosphate (cGMP) in the regulation of IOP and in the pathophysiology of POAG will be discussed.

Differential expression of genes in cells cultured from juxtacanalicular trabecular meshwork and Schlemm's canal

PURPOSE

The purpose of this study was to distinguish differences in gene expression between cells cultured from the juxtacanalicular trabecular meshwork (JCTM) and those from Schlemm's canal (SC), to gain clues to differences between those cell types, and to add to our baseline knowledge of gene expression differences in these cell types for later comparison between cells from nonprimary open-angle glaucoma (POAG) and POAG outflow tissues.

METHODS

A set of JCTM and SC cells was cultured from each of 2 donor eyes by an explant method, grown to passage 3, and frozen in liquid nitrogen. The cells were thawed, total RNA was extracted, and the probes made from total RNAs were hybridized to MICROMAX human cDNA microarray slides in 2 separate trials. Differentially expressed genes were analyzed using PubMed, Prosite, and IPA software, and the expression of several of the genes including intercellular adhesion molecule-1 (ICAM-1), tenascin, and β-spectrin was assessed by immunofluorescence.

RESULTS

Schlemm's canal cells differentially expressed ICAM-1, spectrin, complement, fibulin-1, and several genes consistent with an endothelial origin in both arrays, while the JCTM cells more often overexpressed genes consistent with contractile, matrix function, and neural character. At the same time, many genes highly expressed in the first array were not highly overexpressed in the second. One highly overexpressed gene in the JCTM in both arrays, that for heparan sulfate 3-O-sulfotransferase-1 precursor, is thought to be somewhat unique, and could affect the glycosaminoglycan functionality in the extracellular matrix (ECM).

CONCLUSIONS

We found generally good agreement between the 2 array trials, but some contradictions as well. Many of the genes overexpressed in each cell type had been described in earlier work, but several were new. Tables of genes, grouped by cellular function, and the complete datasets are provided for the development of new hypotheses.

Role of the APOE ε2/ε3/ε4 polymorphism in the development of primary open-angle glaucoma: evidence from a comprehensive meta-analysis

Primary open-angle glaucoma (POAG) is one of the leading causes of blindness worldwide. The association between the APOE ε2/ε3/ε4 polymorphism and the risk of POAG has been widely reported, but the results of previous studies remain controversial. To comprehensively evaluate the APOE ɛ2/ɛ3/ε4 polymorphism on the genetic risk for POAG, we performed a systematic review and meta-analysis of previously published studies. The PubMed and Web of Science databases were systematically searched to identify relevant studies. Data were extracted from these studies and odds ratios with corresponding 95% confidence intervals were computed to estimate the strength of the association. Stratified analyses according to ethnicity and sensitivity analyses were also conducted for further confirmation. A total of nine studies were eligible for the meta-analysis, and these studies included data on 1928 POAG cases and 1793 unrelated match controls. The combined results showed that there were no associations between the APOE ε2/ε3/ε4 polymorphism and POAG risk in any of the 10 comparison models. The analysis that was stratified by ethnicity subgroups also failed to reveal a significant association. The sensitivity analysis confirmed the stability and reliability of the findings. There was no risk of publication bias. Our meta-analysis provides strong evidence that the APOE ε2/ε3/ε4 polymorphism is not associated with POAG susceptibility in any populations.

Neurodegenerative Genes Polymorphisms of the -491A/T APOE, the -877T/C APP and the Risk of Primary Open-angle Glaucoma in the Polish Population

BACKGROUND

Glaucoma is characterized by optic neuropathy of the retinal ganglion cell. It may be possible that β-amyloid (Aβ) and apolipoprotein E (APOE), the main proteins of the pathogenesis of AD, play a role in glaucoma development. The aim of this study was to evaluate a relationship between the APP and APOE gene polymorphisms and the risk of primary open-angle glaucoma (POAG) occurrence.

MATERIALS AND METHODS

The study consisted of 183 patients with POAG and 209 healthy subjects. Genomic DNA was extracted from peripheral blood. Analysis of the gene polymorphisms was performed using PCR-RFLP.

RESULTS

We found a statistically significant increase of the -491 T allele frequency (p=0.02; OR=1.48; 95% CI=1.06-2.08) of APOE in POAG compared to healthy controls. There were no differences in the genotype and allele distributions and odds ratios of the APP polymorphism between patients and controls group. We also found an association between APOE polymorphic variant and retinal nerve fiber layer (RNFL). There was a statistically significant difference in the APOE gene A/T genotype frequency in the early POAG stage and middle-advanced POAG stage in comparison to the advanced POAG stage (p=0.04; OR=3.38; 95% CI=1.04-10.97).

CONCLUSIONS

The -491 T allele of APOE polymorphism may be associated with a risk of POAG occurrence in the Polish population.

Glaucoma, Alzheimer disease and other dementia: a longitudinal analysis

PURPOSE

To evaluate the risk of developing Alzheimer disease (AD) or other dementia in patients diagnosed with open-angle glaucoma (OAG) in a nationally representative longitudinal sample of elderly persons.

METHODS

This retrospective cohort study (January 1, 1994-December 31, 2007) used Medicare 5% claims data. We identified beneficiaries aged 68+ years who had at least two claims with diagnoses of OAG and no Alzheimer or other dementia in 1994, using a 3-year look-back period between 1991 and 1993 (n = 63,235) and beneficiaries matched on age, sex, race, and Charlson index without a diagnosis of OAG throughout the observational period (n = 63,235), using propensity score matching. Using a Cox Proportional Hazards model, we analyzed time to AD diagnosis and time to AD or other dementia diagnosis.

RESULTS

Elderly individuals diagnosed with OAG did not have an increased rate of AD and other dementia diagnosis compared to those without OAG during a 14-year follow-up period, even after controlling for relevant covariates present at baseline.

CONCLUSIONS

Individuals aged 68+ years diagnosed with OAG have a decreased rate of AD or other dementia diagnosis compared to control patients without an OAG diagnosis. Although OAG and AD are both age-related neurodegenerative diseases, our findings do not support a positive association.

Current concepts on primary open-angle glaucoma genetics: a contribution to disease pathophysiology and future treatment

Glaucoma is a common, complex, heterogenous disease and it constitutes the major cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG) is the most common type of glaucoma in all populations. Most of the molecular mechanisms leading to POAG development are still unknown. Gene mutations in various populations have been identified by genetic studies and a genetic basis for glaucoma pathogenesis has been established. Linkage analysis and association studies are genetic approaches in the investigation of the genetic basis of POAG. Genome-wide association studies (GWAS) are more powerful compared with linkage analysis in discovering genes of small effect that might contribute to the development of the disease. POAG links to at least 20 genetic loci, but only 2 genes identified in these loci, myocilin and optineurin, are considered as well-established glaucoma-causing genes, whereas the role of other loci, genes, and variants implicated in the development of POAG remains controversial. Gene mutations associated with POAG result in retinal ganglion cell death, which is the common outcome of pathogenetic mechanisms in glaucoma. In future, if the sensitivity and specificity of genotyping increases, it may be possible to screen individuals routinely for disease susceptibility. This review is an update on the latest progress of genetic studies associated with POAG. It emphasizes the correlation of recent achievements in genetics with glaucoma pathophysiology, glaucoma treatment perspectives, and the possibility of future prevention of irreversible visual loss caused by the disease.

Keeping an eye on myocilin: a complex molecule associated with primary open-angle glaucoma susceptibility

MYOC encodes a secretary glycoprotein of 504 amino acids named myocilin. MYOC is the first gene to be linked to juvenile open-angle glaucoma (JOAG) and some forms of adult-onset primary open-angle glaucoma (POAG). The gene was identified as an up-regulated molecule in cultured trabecular meshwork (TM) cells after treatment with dexamethasone and was originally referred to as trabecular meshwork-inducible glucocorticoid response (TIGR). Elevated intraocular pressure (IOP), due to decreased aqueous outflow, is the strongest known risk factor for POAG. Increasing evidence showed that the modulation of the wild-type (wt) myocilin protein expression is not causative of glaucoma while some misfolded and self-assembly aggregates of mutated myocilin may be associated with POAG in related or unrelated populations. The etiology of the disease remains unclear. Consequently, a better understanding of the molecular mechanisms underlyingPOAG is required to obtain early diagnosis, avoid potential disease progression, and develop new therapeutic strategies. In the present study, we review and discuss the most relevant studies regarding structural characterizations, expressions, molecular interactions, putative functions of MYOC gene and/or its corresponding protein in POAG etiology.

Complex genetic mechanisms in glaucoma: an overview

Glaucomas comprise a group of hereditary optic neuropathies characterized by progressive and irreversible visual field loss and damage to the optic nerve head. It is a complex disease with multiple molecular mechanisms underlying its pathogenesis. Genetic heterogeneity is the hallmark of all glaucomas and multiple chromosomal loci have been linked to the disease, but only a few genes have been characterized, viz. myocilin (MYOC), optineurin (OPTN), WDR36 and neurotrophin-4 (NTF4) in primary open angle glaucoma (POAG) and CYP1B1 and LTBP2 in congenital and developmental glaucomas. Case-control-based association studies on candidate genes involved in different stages of glaucoma pathophysiology have indicated a very limited involvement. The complex mechanisms leading to glaucoma pathogenesis indicate that it could be attributed to multiple genes with varying magnitudes of effect. In this review, we provide an appraisal of the various efforts in unraveling the molecular mystery in glaucoma and also some future directions based on the available scientific knowledge and technological developments.

Myocilin mt.1 gene promoter single nucleotide polymorphism (-1000C>G) in Brazilian patients with primary open angle glaucoma

BACKGROUND

The myocilin (MYOC) gene promoter polymorphism -1000C>G (MYOC mt.1) can be associated with faster progression of primary open angle glaucoma (POAG). The purpose of this study was to investigate the MYOC mt.1 in Brazilian patients with POAG and to evaluate its possible role on the phenotype and the severity of the disease.

MATERIAL AND METHODS

One hundred sixty-seven POAG patients and 130 normal controls were enrolled. DNA samples were prepared and the MYOC mt.1 polymorphism was screened by real-time polymerase chain reaction (RT-PCR) in an Single-nucleotide polymorphism (SNP) assay. Frequencies of the MYOC mt.1 promoter polymorphism were determined for both groups and compared by Fisher's exact test and Chi-square test with Yate's correction. Intraocular pressure (IOP), cup-to-disc ratio (C/D), number of glaucoma medications, and number of glaucoma surgeries were compared between MYOC mt.1 carriers and non-carriers.

RESULTS

MYOC mt.1 genotype frequencies did not differ between POAG and controls (P  =  0.420); 14.6% of controls and 16.4% of POAG patients were MYOC mt.1 carriers (CG or GG). Frequencies of the G allele were similar between glaucomatous patients and controls (7.3% and 9.2%, respectively; P  =  0.477). Among POAG patients, there were no differences in mean C/D ratio, IOP, number of glaucoma medications, and surgical procedures for IOP control between carries and non-carriers of the MYOC mt.1 promoter polymorphism (p>0.05).

CONCLUSION

The G allele of the MYOC mt.1 promoter polymorphism was equally distributed among POAG patients and healthy subjects and it is possibly unrelated to the risk and severity of disease in the Brazilian population.

Apolipoprotein E and central nervous system disorders: reviews of clinical findings

Dementia is a major health problem in developed countries with over 25 million people affected worldwide and probably over 75 million people at risk during the next 20 years. Alzheimer's disease (AD) is the most frequent cause of dementia (50-70%), followed by vascular dementia (30-40%), and mixed dementia (15-20%). AD pathogenesis is still to be elucidated but it is believed to be the complex interaction between genetic and environmental factors in later life. Three causative genes for familial AD have been identified: amyloid precursor protein, presenilin-1, and presenilin-2. There are 150 genes involved with increased neuronal vulnerability to premature death in the AD brain. Among these susceptibility genes, the apolipoprotein E (ApoE) gene is the most prevalent as a risk for AD pathogenic process in which complex interactions between genetic and environmental factors are involved, leading to a cascade of pathogenic events converging in final pathways to premature neuronal death. Some of these mechanisms are common to several neurodegenerative disorders that differ depending upon the genes affected and the involvement of environmental conditions. ApoE is a key lipoprotein in lipid and cholesterol metabolism and it is also the major risk gene for AD and many other central nervous system disorders. The pathogenic role of ApoE-4 is still to be clarified; however, diverse evidence suggests that ApoE may play pleiotropic functions in dementia and central nervous system disorders.

Identification of a novel mutation in the NTF4 gene that causes primary open-angle glaucoma in a Chinese population

PURPOSE

Neurotrophin-4 protein (NT-4) plays a role in the protection of retinal ganglion cells by activating tyrosine kinase B (TrkB) receptors. A recent study identified mutations within the neurotrophin-4 (NTF4) gene to account for 1.7% of primary open-angle glaucoma (POAG) in Europeans. The aim of this study was to investigate the frequency of NTF4 mutations in Chinese POAG patients.

METHODS

One hundred-seventy-four Chinese subjects with POAG and 91 normal Chinese subjects were recruited. POAG was defined by the presence of glaucomatous optic neuropathy, open angles on gonioscopy, and absence of secondary causes of glaucoma. The single coding exon of NTF4 was PCR amplified and subjected to bidirectional sequencing in all subjects.

RESULTS

The mean age of POAG patients was 66.0+/-13.0 years (range 25-96 years) and that of controls was 67.1+/-4.6 years (range 60-85 years). We identified a novel NTF4 missense mutation substituting leucine by serine at codon 113 (Leu113Ser) caused by a c.338T>C mutation in a single patient with unilateral POAG, who presented with a baseline intraocular pressure of 25 mmHg, a vertical cup-to-disc ratio of 0.9 and an inferior hemifield defect in the affected eye. Structural analysis indicated that the Leu113Ser mutation is likely to alter the NT-4 protein structure near the TrkB binding site and disrupts the formation of the NT-4-TrkB complex required for the activation of TrkB.

CONCLUSIONS

Identification of a single mutation in our study suggests that NTF4 mutations are a rare cause of POAG (0.6%, 95%CI 0.02%-3.16%) in Chinese people.

Genetic bases for glaucoma

Glaucoma is the leading cause of visual impairment and blindness throughout the world. Primary open angle glaucoma (POAG; MIM 137760) is the main type of glaucoma in most populations, and more than 20 genetic loci for POAG have been reported. Only three causative genes have been identified in these loci, viz. myocilin (MYOC), optineurin (OPTN), and WD repeat domain 36 (WDR36). However, mutations in these genes account for only a small percentage of the patients with POAG. Some of these glaucoma cases have a Mendelian inheritance pattern, and a considerable fraction of the cases result from a large number of variants in several genes each contributing small effects. Glaucoma is considered to be a common disease such as diabetes mellitus, coronary disease, Crohn disease, and several( )common cancers. The main technological approaches used to identify the genes associated with glaucoma are the candidate gene approach, linkage analysis, case-control association study, and genome-wide association study. Association studies have found about 27 genes related to POAG, but the glaucoma-causing effects of these genes need to be investigated in more detail. The current trend is to use case-control association studies or genome-wide association studies to map the genes associated with glaucoma. Such studies are expected to greatly advance our understanding of the genetic basis of glaucoma, and to provide information on the effectiveness of glaucoma therapy. This review gives an overview on the genetic aspects of glaucoma.

Molecular complexity of primary open angle glaucoma: current concepts

Glaucoma is a group of heterogeneous optic neuropathies with complex genetic basis. Among the three principle subtypes of glaucoma, primary open angle glaucoma (POAG) occurs most frequently. Till date, 25 loci have been found to be linked to POAG. However, only three underlying genes (Myocilin, Optineurin and WDR36) have been identified. In addition, at least 30 other genes have been reported to be associated with POAG. Despite strong genetic influence in POAG pathogenesis, only a small part of the disease can be explained in terms of genetic aberration. Current concepts of glaucoma pathogenesis suggest it to be a neurodegenerative disorder which is triggered by different factors including mechanical stress due to intra-ocular pressure, reduced blood flow to retina, reperfusion injury, oxidative stress, glutamate excitotoxicity, and aberrant immune response. Here we present a mechanistic overview of potential pathways and crosstalk between them operating in POAG pathogenesis.

Induction of amyloid precursor protein by the neurotoxic peptide, amyloid-beta 25-35, causes retinal ganglion cell death

Patients with Alzheimer's disease (AD) show a significantly increased incidence of glaucoma. AD is also associated with the occurrence of the neurotoxic peptide amyloid beta (Abeta). Therefore, we investigated whether Abeta is associated with retinal cell death in a retinal ganglion cell line (RGC-5). Treatment with Abeta(25-35), a neurotoxic fragment of Abeta, induced cell death in RGC-5 in both a concentration- and time-dependent manner. The amount of amyloid precursor protein was increased by treatment of RGC-5 and primary culture of mouse cortical neurons with fibril Abeta(25-35) and Abeta(1-42), which is a putative physiological neurotoxic fragment of Abeta present in AD. Amyloid precursor protein knockdown inhibited the cell death induced by Abeta(25-35). Treatment with Abeta(25-35) increased the amount of intracellular Abeta(1-40) and Abeta(1-42), while beta- and gamma-secretase inhibitors reduced cell death. Thus, the regulation of Abeta can be viewed as a new therapeutic target for glaucoma, especially in patients with coincident AD.

Methylenetetrahydrofolate Reductase Genetic Polymorphisms in Patients with Primary Open-Angle Glaucoma

PURPOSE

Hyperhomocysteinemia has been found in patients with primary open-angle glaucoma. The purpose of the present study was to determine if hyperhomocysteinemia-associated polymorphisms of the methylenetetrahydrofolate reductase gene (MTHFR) are overrepresented in primary open-angle glaucoma.

METHODS

Patients with primary open-angle glaucoma (n = 243) and controls (n = 187) were analyzed for the MTHFR 677 C > T and 1298 A > C polymorphisms using minisequencing technique.

RESULTS

No significant differences were observed in allele and genotype frequencies of the MTHFR 677C > T and 1298A > C polymorphisms between controls and the primary open-angle glaucoma group.

CONCLUSIONS

If hyperhomocysteinemia is important in the pathogenesis of glaucoma, this study does not support a role for MTHFR polymorphisms in this context.

Association of polymorphisms in APOE, p53, and p21 with primary open-angle glaucoma in Turkish patients

PURPOSE

To investigate the association between Apolipoprotein E (APOE), tumor suppressor protein p53 (p53), and cyclin-dependent kinase inhibitor 1A (p21) genes and primary open-angle glaucoma (POAG) in a cohort of Turkish subjects.

METHODS

Seventy-five POAG patients (49 women, 26 men) and 119 healthy subjects (67 women, 52 men) were genotyped with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Allele and genotype frequencies between healthy subjects and glaucoma patients were compared by the chi(2) test, and intraocular pressure (IOP), cup/disc ratio (C/D) and visual field indices (MD and PSD) were compared among different APOE, p53, and p21 genotypes in POAG group. A p value <0.05 was considered as statistically significant.

RESULTS

The mean ages were 63.8+/-9.5 and 61.8+/-10.2 years in POAG and control groups, respectively (p=0.18). There were no significant differences in the distribution of APOE, p53, and p21 genotypes between the healthy subjects and POAG patients (p=0.38, p=0.12, and p=0.2, respectively). There were no significant differences in maximum IOP, MD, and PSD values among different groups of p53 and p21 genotypes (p>0.05). POAG subjects with the epsilon2epsilon3 genotype had a worse PSD value (median=2.2) than those with the epsilon3epsilon4 genotype (median=1.77; p=0.01) and POAG subjects with the epsilon3epsilon3 genotype had worse MD and PSD values (median= -7.4 and 3.4, respectively) than those with the epsilon3epsilon4 genotype (median= -4.1 and 1.77, respectively; p=0.034 and 0.028, respectively).

CONCLUSIONS

Our study found no link between polymorphisms in APOE, p53, and p21 genes and POAG in Turkish patients, although a larger sample is required to elucidate the role of these polymorphisms in the pathogenesis and course of glaucoma.

Glaucoma-associated myocilin: a better understanding but much more to learn

Over a decade has passed since myocilin was identified as the first gene linked to early and late-onset primary open-angle glaucoma. During this time, considerable effort has been put forth to understand the functional role myocilin has in normal and glaucomatous eyes. Myocilin is expressed in many ocular and non-ocular tissues, is found in both intracellular and extracellular spaces, and has been linked to elevations in intraocular pressure. Mutations in the myocilin gene that have been associated with glaucoma appear to confer a gain-of-functional activity rather than loss of function. Unfortunately, what the normal function of myocilin is and how alterations in the function can confer a glaucoma phenotype have yet to be elucidated. We will review the current understanding of myocilin with special emphasis on the structural makeup of the myocilin gene and protein, its possible physiological roles internal and external to ocular cells, the regulation of intraocular pressure as evidenced through the use of perfusion culture systems and animal models, and as a causative agent in some forms of glaucoma.

Multiple gene polymorphisms analysis revealed a different profile of genetic polymorphisms of primary open-angle glaucoma in northern Chinese

PURPOSE

To evaluate the individual and interactive effects of polymorphisms in the myocilin (MYOC),optineurin (OPTN), WD repeat domain 36 (WDR36), and apolipoprotein E (APOE) genes on primary open-angle glaucoma (POAG) in northern Chinese.

METHODS

Northern Chinese study subjects, 176 POAG patients and 200 controls, were recruited for screening of the coding exons and splicing regions of MYOC. Five single nucleotide polymorphisms (SNPs) in OPTN (M98K, R545Q, IVS5+38T>G, IVS8-53T>C, and IVS15+10G>A), one SNP in WDR36 (IVS5+30C>T) as well as the APOE promoter and epsilon2/epsilon3/epsilon4 polymorphisms were also examined. Association analysis was performed by using chi(2) analysis. High-order gene-gene interaction was also analyzed using the multifactor dimensionality reduction (MDR) method.

RESULTS

In MYOC, 22 variants were identified. Four of them were novel but found in controls only. The missense mutation, Val53Ala, is likely a glaucoma causing mutation, accounting for 0.6% of cases. No individual polymorphism in OPTN, WDR36, or APOE was associated with POAG. MDR analysis identified a best 6-factor model for POAG: MYOC IVS2+35A>G, OPTN Met98Lys, OPTN IVS5+38T>G, OPTN IVS8-53T>C, WDR36 IVS5+30C>T, and APOE -491A>T.

CONCLUSIONS

The association pattern between the genes, MYOC, OPTN, WDR36, and APOE, and POAG in northern Chinese is different from that of southern Chinese. Disease-causing mutations in MYOC accounted for a small proportion of northern Chinese POAG patients. Common polymorphisms in these genes were not associated with POAG individually but might interactively contribute to the disorder, supporting a polygenic etiology.

The genetics of primary open-angle glaucoma: a review

Glaucoma is the major cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG), as the most prevalent form of glaucoma, is a complex inherited disorder and affects more than 2 million individuals in the United States. It has become increasingly clear that a host of genetic as well as environmental factors are likely to contribute to the phenotype. A number of chromosomal and genetic associations have been reported for POAG. This review examines what is currently known about the underlying genetic structure, what remains to be learned, and how this may affect our medical management of this major blinding disease.

Contributions of MYOC and CYP1B1 mutations to JOAG

PURPOSE

To investigate the role of MYOC and CYP1B1 in Iranian juvenile open angle glaucoma (JOAG) patients.

METHODS

Twenty-three JOAG probands, their available affected and unaffected family members, and 100 ethnically matched control individuals without history of ocular disease were recruited. Clinical examinations of the probands included slit lamp biomicroscopy, intraocular pressure (IOP) measurement, gonioscopic evaluation, fundus examination, and perimetry measurement. Familial cases were classified according to the mode of inheritance. Exons of MYOC and CYP1B1 were sequenced, and novel variations assessed in the control individuals. Potential disease-associated variations were tested for segregation with disease status in available family members.

RESULTS

The mode of inheritance of the disease in the families of four probands (17.4%) appeared to be autosomal dominant and in at least eight (34.8%) to be autosomal recessive. Four patients carried MYOC mutations, and an equal number carried CYP1B1 mutations. The MYOC mutations were heterozygous; two of them (p.C8X and p.L334P) are novel, and one codes for the shortest truncated protein so far reported. Autosomal recessive inheritance was consistent with inheritance observed in families of patients carrying CYP1B1 mutations. All these patients carried homozygous mutations.

CONCLUSIONS

MYOC and CYP1B1 contributed equally to the disease status of the Iranian JOAG patients studied. The contribution of the two genes appeared to be independent in that no patient carried mutations in both genes. The fraction of Iranian patients carrying MYOC mutations was comparable to previously reported populations.

Role of CYP1B1 in Glaucoma

Glaucoma is a leading cause of blindness, estimated to affect 60 million people by 2010, and represents a heterogeneous group of neurodegenerative disease. The two major types of glaucoma include primary open-angle glaucoma (POAG) and primary congenital glaucoma (PCG). A genetically heterogeneous group of developmental disorders known as anterior segment dysgenesis (ASD) have been reported to be associated with increased intraocular pressure (IOP) and glaucoma. These include Peters' anomaly, Rieger's anomaly, aniridia, iris hypoplasia, and iridogoniodysgenesis. Genetic linkage analysis and mutation studies have identified CYP1B1 as a causative gene in PCG, as a modifier gene in POAG, and, on rare occasions, as causative gene in POAG as well as in several ASD disorders. CYP1B1-deficient mice exhibit abnormalities in their ocular drainage structure and trabecular meshwork that are similar to those reported in human PCG patients. Accordingly, it is speculated that diminished or absent metabolism of key endogenous CYP1B1 substrates adversely affects the development of the trabecular meshwork. CYP1B1 protein is involved in the metabolism of steroids, retinol and retinal, arachidonate, and melatonin. The conserved expression of CYP1B1 in both murine and human eyes, its higher expression in fetal than adult eyes, and its biochemical properties are consistent with this hypothesis. The exact role of CYP1B1 in the pathogenesis of glaucoma and other ASD disorders remains to be elucidated.

Association between open-angle glaucoma and gene polymorphism for heat-shock protein 70-1

PURPOSE

Heat-shock proteins (HSPs) or antibodies against them may contribute to glaucomatous optic neuropathy. We investigated the associations of HSP70-1 polymorphisms with open-angle glaucoma (OAG) in a Japanese population.

METHODS

In 241 normal Japanese controls and 501 Japanese OAG patients, including 211 with primary open-angle glaucoma (POAG) and 290 with normal-tension glaucoma (NTG), two single-nucleotide polymorphisms, A-110C and G+190C, of HSP70-1 were identified by using an Invader assay and polymerase chain reaction-restriction fragment length polymorphism, respectively. Genotype distributions were compared between controls and OAG patients. Age at diagnosis, untreated maximum intraocular pressure, and visual field defects at diagnosis were examined for associations with the polymorphisms.

RESULTS

Distribution of the A-110C genotype (AA versus AC+CC) differed significantly between controls and OAG patients (P = 0.007), POAG patients (P = 0.007), or NTG patients (P = 0.032). The genotype distribution of the G+190C polymorphism did not differ significantly between the controls and any patient group. No significant differences in the clinical characteristics of the patients were detected between genotype-defined groups by logistic regression analysis.

CONCLUSION

The A-110C polymorphism of HSP70-1 may be associated with OAG pathogenesis in Japanese patients.

[Primary open-angle glaucoma and systemic diseases]

The exact pathomechanism of primary open-angle glaucoma (POAG) is still not completely understood. Besides elevated intraocular pressure, which has been identified as a major risk factor, there is mounting evidence for the involvement of systemic factors in the development of glaucomatous damage. Systemic peculiarities described in POAG include cardiovascular, endocrine, neurodegenerative, and sleep alterations. However, some of the studies available on systemic findings in glaucoma patients are contradictory, making further research necessary to identify the exact role of such disturbances in the pathogenesis of the damage. Another difficulty is that many studies are limited by their small sample size, their retrospective nature, and potential selection bias, thus making data interpretation more difficult. Moreover, it is not always clear whether we are dealing with coincidence or a true association between glaucoma and a particular systemic disease. Nevertheless, there is ample evidence for the involvement of vascular factors such as vascular dysregulation and blood pressure in the pathogenesis of POAG.

Interaction between two glaucoma genes, optineurin and myocilin

Myocilin (MYOC) and optineurin (OPTN) are two genes linked to glaucoma, a major blinding disease. To investigate the possible molecular interactions between MYOC and OPTN genes, we over-expressed MYOC and examined its effect on the level of endogenous OPTN in human trabecular meshwork (TM) cells and vice versa. We noted that over-expressing MYOC did not affect the OPTN level, whereas OPTN over-expression induced an up-regulation of the endogenous MYOC. This induction was also observed in other ocular and non-ocular cell types including PC12 cells. The endogenous levels of both OPTN and MYOC genes were in addition found increased when PC12 cells underwent differentiation upon treatment with nerve growth factor (NGF). Over-expression of OPTN resulted in prolonged turnover rate of MYOC mRNA but had little effect on the promoter activity of the MYOC gene. The over-expressed OPTN was localized in the cytoplasm, not translocated into the nucleus. These results indicate that interaction exists between OPTN and MYOC genes. Regulation of MYOC expression by OPTN is achieved primarily through control of the mRNA stability.

Effects of APOE and CHRNA4 genotypes on retinal nerve fibre layer thickness at the optic disc and on risk for developing exfoliation syndrome

PURPOSE

To investigate whether CHRNA4 and APOE genotypes influence retinal nerve fibre layer (RNFL) thickness at the optic disc, intraocular pressure (IOP) and the development of exfoliation syndrome (XFS).

METHODS

A sample of 88 healthy adults (aged 50-75 years) genotyped for polymorphisms of APOE and CHRNA4 underwent an eye examination including slit-lamp examination and fundus photography, as well as measurements of visual acuity, refraction, IOP and RNFL thickness at the optic disc by optical coherence tomography. The Fisher-Boschloo unconditional full multinomial test and two sample t-tests were used in the statistical analyses.

RESULTS

There was no correlation between CHRNA4 and APOE genotypes and average RNFL thickness at the optic disc in the two eyes. Mean IOP in the eyes of APOE2 carriers was 13.18 mmHg, whereas that in the eyes of non-APOE2 carriers, at 14.82 mmHg, was significantly higher (p = 0.014). Exfoliation syndrome was found in one or both eyes in 15 persons. The presence of XFS was less likely in CC carriers of the CHRNA4 gene than in TT and TC carriers (p = 0.049).

CONCLUSIONS

We found no significant difference in RNFL thickness at the optic disc in the different genotype carriers of the APOE and CHRNA4 genes, and thereby no evidence for increased loss of ganglion cells in the retina as an effect of these genes. APOE2 carriers had significantly lower IOP than non-APOE2 carriers. However, both values are within the normal range and RNFL thickness measurements at the optic disc showed no difference between these two groups. In our study population, CC carriers of the CHRNA4 gene were less likely to develop XFS.

Complex genetics of complex traits: the case of primary open-angle glaucoma

Glaucoma, which is a complex heterogeneous disease, presents an ideal case for genetic investigation. Primary open-angle glaucoma (POAG) is the commonest subtype and will be the focus of this review. When detected early, POAG is amenable to therapeutic intervention. Unfortunately, current population-based clinical screening lacks efficacy. If individuals with a genetic predisposition for developing POAG can be identified, then efficient and cost-effective population-based screening programs could be designed. Although considerable inroads have been made in understanding the natural history of POAG caused by mutations in the myocilin and optineurin genes, other POAG genes accounting for most cases remain to be identified. This review explores the genetic mechanisms that have been unequivocally linked to the glaucomatous process and then discusses potential avenues for future breakthroughs.

Association of Apolipoprotein E Polymorphisms With Normal Tension Glaucoma in a Chinese Population

PURPOSE

To evaluate the role of apolipoprotein E (APOE) polymorphisms in primary open angle glaucoma (POAG).

METHODS

A cohort of 400 unrelated Chinese POAG patients was examined, including 294 cases of high tension glaucoma (HTG) and 106 with normal tension glaucoma (NTG). Also studied were 300 unrelated Chinese control subjects. The genotypes of the APOE polymorphisms in exon 4 and in the promoter at positions -491, -427, and -219 were determined by polymerase chain reaction and restriction endonuclease analysis. Frequencies of the genotypes were compared between patients and controls by chi test or Fisher exact test. The association of APOE polymorphisms with POAG phenotypes including age at diagnosis, intraocular pressure (IOP) at diagnosis, highest IOP, cup-disc ratio, and visual field score was investigated by the Kruskal-Wallis test.

RESULTS

No significant difference was detected in the frequencies of APOE promoter polymorphisms between POAG patients and control subjects (P>0.0125). For the exon 4 polymorphism, when compared with control subjects, the frequency of epsilon 4 carriers was significantly lower in patients with NTG (P=0.008; odds ratio=0.36, 95% confidence interval=0.17, 0.79) but not in HTG (P=0.07). Compared with -219TT, the -219G carriers had a significant higher age at diagnosis (P=0.0046). No significant association was found between other APOE polymorphisms and POAG phenotypes (P>0.07).

CONCLUSIONS

Our findings suggest that the APOE epsilon 4 allele confers a protective effect against NTG, whereas the APOE promoter polymorphisms do not contribute to POAG risk. However, the APOE -219G carriers tended to have later-onset POAG.

A Sick Eye in a Sick Body? Systemic Findings in Patients with Primary Open-angle Glaucoma

Despite intense research, the pathogenesis of primary open-angle glaucoma (POAG) is still not completely understood. There is ample evidence for a pathophysiological role of elevated intraocular pressure; however, several systemic factors may influence onset and progression of the disease. Systemic peculiarities found in POAG include alterations of the cardiovascular system, autonomic nervous system, immune system, as well as endocrinological, psychological, and sleep disturbances. An association between POAG and other neurodegenerative diseases, such as Alzheimer disease and Parkinson disease, has also been described. Furthermore, the diagnosis of glaucoma can affect the patient's quality of life. By highlighting the systemic alterations found in POAG, this review attempts to bring glaucoma into a broader medical context.