Education influences the role of genetics in myopia

Myopia is a complex inherited ocular trait resulting from an interplay of genes and environmental factors, most of which are currently unknown. In two independent population-based cohorts consisting of 5,256 and 3,938 individuals from European descent, we tested for biological interaction between genetic predisposition and level of education on the risk of myopia. A genetic risk score was calculated based on 26 myopia-associated single nucleotide polymorphisms recently discovered by the Consortium for Refractive Error and Myopia. Educational level was obtained by questionnaire and categorized into primary, intermediate, and higher education. Refractive error was measured during a standardized ophthalmological examination. Biological interaction was assessed by calculation of the synergy index. Individuals at high genetic risk in combination with university-level education had a remarkably high risk of myopia (OR 51.3; 95 % CI 18.5–142.6), while those at high genetic risk with only primary schooling were at a much lower increased risk of myopia (OR 7.2, 95 % CI 3.1–17.0). The combined effect of genetic predisposition and education on the risk of myopia was far higher than the sum of these two effects (synergy index 4.2, 95 % CI 1.9–9.5). This epidemiological study provides evidence of a gene-environment interaction in which an individual’s genetic risk of myopia is significantly affected by his or her educational level.

Prediction of age-related macular degeneration in the general population: the Three Continent AMD Consortium

PURPOSE

Prediction models for age-related macular degeneration (AMD) based on case-control studies have a tendency to overestimate risks. The aim of this study is to develop a prediction model for late AMD based on data from population-based studies.

DESIGN

Three population-based studies: the Rotterdam Study (RS), the Beaver Dam Eye Study (BDES), and the Blue Mountains Eye Study (BMES) from the Three Continent AMD Consortium (3CC).

PARTICIPANTS

People (n = 10,106) with gradable fundus photographs, genotype data, and follow-up data without late AMD at baseline.

METHODS

Features of AMD were graded on fundus photographs using the 3CC AMD severity scale. Associations with known genetic and environmental AMD risk factors were tested using Cox proportional hazard analysis. In the RS, the prediction of AMD was estimated for multivariate models by area under receiver operating characteristic curves (AUCs). The best model was validated in the BDES and BMES, and associations of variables were re-estimated in the pooled data set. Beta coefficients were used to construct a risk score, and risk of incident late AMD was calculated using Cox proportional hazard analysis. Cumulative incident risks were estimated using Kaplan-Meier product-limit analysis.

MAIN OUTCOME MEASURES

Incident late AMD determined per visit during a median follow-up period of 11.1 years with a total of 4 to 5 visits.

RESULTS

Overall, 363 participants developed incident late AMD, 3378 participants developed early AMD, and 6365 participants remained free of any AMD. The highest AUC was achieved with a model including age, sex, 26 single nucleotide polymorphisms in AMD risk genes, smoking, body mass index, and baseline AMD phenotype. The AUC of this model was 0.88 in the RS, 0.85 in the BDES and BMES at validation, and 0.87 in the pooled analysis. Individuals with low-risk scores had a hazard ratio (HR) of 0.02 (95% confidence interval [CI], 0.01-0.04) to develop late AMD, and individuals with high-risk scores had an HR of 22.0 (95% CI, 15.2-31.8). Cumulative risk of incident late AMD ranged from virtually 0 to more than 65% for those with the highest risk scores.

CONCLUSIONS

Our prediction model is robust and distinguishes well between those who will develop late AMD and those who will not. Estimated risks were lower in these population-based studies than in previous case-control studies.

Corticosteroids and open-angle glaucoma in the elderly: a population-based cohort study

BACKGROUND

It is largely unknown if corticosteroid-induced open-angle glaucoma (OAG) is an entity that is limited to a few susceptible individuals or whether it contributes significantly to the overall population burden of OAG.

OBJECTIVE

The aim of this study was to determine whether there is an association between corticosteroid use and the incidence of OAG in the general elderly population.

METHODS

A prospective population-based cohort study was conducted in a general community setting. 3,939 participants of the Rotterdam Study aged 55 years and older for whom data from ophthalmic examinations at baseline and follow-up were available and who did not have glaucoma at baseline were included (baseline examination from 1991 to 1993; follow-up examinations from 1997 to 1999 and from 2002 to 2006). Ophthalmic examinations, including measurement of the intraocular pressure, assessment of the optic nerve head and perimetry, were performed at baseline and follow-up. The use of corticosteroids was monitored continuously during follow-up. Corticosteroids were stratified into five groups: ophthalmic steroids, inhaled steroids, nasal steroids, oral steroids and steroid ointments. Associations between the use of corticosteroids and incident OAG were assessed using logistic regression models. The study outcome measures were the odds ratios (ORs) of associations between the use of corticosteroids and incident OAG.

RESULTS

During a mean follow-up of 9.8 years, 108 participants (2.8%) developed OAG. The median number of steroid prescriptions during follow-up was 2 for ophthalmic, 7 for inhaled, 2 for nasal and 2 for oral steroids, and 3 for steroid ointments. The OR of the use of ophthalmic steroids was 1.04 [95% confidence interval (CI) 0.66, 1.65; p = 0.86], inhaled steroids 0.79 (95% CI 0.42, 1.48; p = 0.46), nasal steroids 1.26 (95% CI 0.74, 2.13; p = 0.40), oral steroids 1.03 (95% CI 0.65, 1.64; p = 0.89) and steroid ointments 0.70 (95% CI 0.47, 1.05; p = 0.086). These analyses were adjusted for age, sex, high myopia and family history of glaucoma. The small median numbers of prescriptions made it difficult to evaluate dose-response relationships.

CONCLUSION

None of the classes of steroids were associated with the incidence of OAG in this elderly population.

Meta-analysis of genome-wide association studies in five cohorts reveals common variants in RBFOX1, a regulator of tissue-specific splicing, associated with refractive error

Visual refractive errors (REs) are complex genetic traits with a largely unknown etiology. To date, genome-wide association studies (GWASs) of moderate size have identified several novel risk markers for RE, measured here as mean spherical equivalent (MSE). We performed a GWAS using a total of 7280 samples from five cohorts: the Age-Related Eye Disease Study (AREDS); the KORA study ('Cooperative Health Research in the Region of Augsburg'); the Framingham Eye Study (FES); the Ogliastra Genetic Park-Talana (OGP-Talana) Study and the Multiethnic Study of Atherosclerosis (MESA). Genotyping was performed on Illumina and Affymetrix platforms with additional markers imputed to the HapMap II reference panel. We identified a new genome-wide significant locus on chromosome 16 (rs10500355, P = 3.9 × 10(-9)) in a combined discovery and replication set (26 953 samples). This single nucleotide polymorphism (SNP) is located within the RBFOX1 gene which is a neuron-specific splicing factor regulating a wide range of alternative splicing events implicated in neuronal development and maturation, including transcription factors, other splicing factors and synaptic proteins.

Genetic loci for retinal arteriolar microcirculation

Narrow arterioles in the retina have been shown to predict hypertension as well as other vascular diseases, likely through an increase in the peripheral resistance of the microcirculatory flow. In this study, we performed a genome-wide association study in 18,722 unrelated individuals of European ancestry from the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium and the Blue Mountain Eye Study, to identify genetic determinants associated with variations in retinal arteriolar caliber. Retinal vascular calibers were measured on digitized retinal photographs using a standardized protocol. One variant (rs2194025 on chromosome 5q14 near the myocyte enhancer factor 2C MEF2C gene) was associated with retinal arteriolar caliber in the meta-analysis of the discovery cohorts at genome-wide significance of P-value <5×10⁻⁸. This variant was replicated in an additional 3,939 individuals of European ancestry from the Australian Twins Study and Multi-Ethnic Study of Atherosclerosis (rs2194025, P-value = 2.11×10⁻¹² in combined meta-analysis of discovery and replication cohorts). In independent studies of modest sample sizes, no significant association was found between this variant and clinical outcomes including coronary artery disease, stroke, myocardial infarction or hypertension. In conclusion, we found one novel loci which underlie genetic variation in microvasculature which may be relevant to vascular disease. The relevance of these findings to clinical outcomes remains to be determined.

Seven new loci associated with age-related macular degeneration

Age-related macular degeneration (AMD) is a common cause of blindness in older individuals. To accelerate the understanding of AMD biology and help design new therapies, we executed a collaborative genome-wide association study, including >17,100 advanced AMD cases and >60,000 controls of European and Asian ancestry. We identified 19 loci associated at P < 5 × 10(-8). These loci show enrichment for genes involved in the regulation of complement activity, lipid metabolism, extracellular matrix remodeling and angiogenesis. Our results include seven loci with associations reaching P < 5 × 10(-8) for the first time, near the genes COL8A1-FILIP1L, IER3-DDR1, SLC16A8, TGFBR1, RAD51B, ADAMTS9 and B3GALTL. A genetic risk score combining SNP genotypes from all loci showed similar ability to distinguish cases and controls in all samples examined. Our findings provide new directions for biological, genetic and therapeutic studies of AMD.

Genome-wide meta-analyses of multiancestry cohorts identify multiple new susceptibility loci for refractive error and myopia

Refractive error is the most common eye disorder worldwide and is a prominent cause of blindness. Myopia affects over 30% of Western populations and up to 80% of Asians. The CREAM consortium conducted genome-wide meta-analyses, including 37,382 individuals from 27 studies of European ancestry and 8,376 from 5 Asian cohorts. We identified 16 new loci for refractive error in individuals of European ancestry, of which 8 were shared with Asians. Combined analysis identified 8 additional associated loci. The new loci include candidate genes with functions in neurotransmission (GRIA4), ion transport (KCNQ5), retinoic acid metabolism (RDH5), extracellular matrix remodeling (LAMA2 and BMP2) and eye development (SIX6 and PRSS56). We also confirmed previously reported associations with GJD2 and RASGRF1. Risk score analysis using associated SNPs showed a tenfold increased risk of myopia for individuals carrying the highest genetic load. Our results, based on a large meta-analysis across independent multiancestry studies, considerably advance understanding of the mechanisms involved in refractive error and myopia.

Identification of a candidate gene for astigmatism

PURPOSE

Astigmatism is a common refractive error that reduces vision, where the curvature and refractive power of the cornea in one meridian are less than those of the perpendicular axis. It is a complex trait likely to be influenced by both genetic and environmental factors. Twin studies of astigmatism have found approximately 60% of phenotypic variance is explained by genetic factors. This study aimed to identify susceptibility loci for astigmatism.

METHODS

We performed a meta-analysis of seven genome-wide association studies that included 22,100 individuals of European descent, where astigmatism was defined as the number of diopters of cylinder prescription, using fixed effect inverse variance-weighted methods.

RESULTS

A susceptibility locus was identified with lead single nucleotide polymorphism rs3771395 on chromosome 2p13.3 (meta-analysis, P = 1.97 × 10(-7)) in the VAX2 gene. VAX2 plays an important role in the development of the dorsoventral axis of the eye. Animal studies have shown a gradient in astigmatism along the vertical plane, with corresponding changes in refraction, particularly in the ventral field.

CONCLUSIONS

This finding advances the understanding of refractive error, and provides new potential pathways to be evaluated with regard to the development of astigmatism.

Insights into the genetic architecture of early stage age-related macular degeneration: a genome-wide association study meta-analysis

Genetic factors explain a majority of risk variance for age-related macular degeneration (AMD). While genome-wide association studies (GWAS) for late AMD implicate genes in complement, inflammatory and lipid pathways, the genetic architecture of early AMD has been relatively under studied. We conducted a GWAS meta-analysis of early AMD, including 4,089 individuals with prevalent signs of early AMD (soft drusen and/or retinal pigment epithelial changes) and 20,453 individuals without these signs. For various published late AMD risk loci, we also compared effect sizes between early and late AMD using an additional 484 individuals with prevalent late AMD. GWAS meta-analysis confirmed previously reported association of variants at the complement factor H (CFH) (peak P = 1.5×10⁻³¹) and age-related maculopathy susceptibility 2 (ARMS2) (P = 4.3×10⁻²⁴) loci, and suggested Apolipoprotein E (ApoE) polymorphisms (rs2075650; P = 1.1×10⁻⁶) associated with early AMD. Other possible loci that did not reach GWAS significance included variants in the zinc finger protein gene GLI3 (rs2049622; P = 8.9×10⁻⁶) and upstream of GLI2 (rs6721654; P = 6.5×10⁻⁶), encoding retinal Sonic hedgehog signalling regulators, and in the tyrosinase (TYR) gene (rs621313; P = 3.5×10⁻⁶), involved in melanin biosynthesis. For a range of published, late AMD risk loci, estimated effect sizes were significantly lower for early than late AMD. This study confirms the involvement of multiple established AMD risk variants in early AMD, but suggests weaker genetic effects on the risk of early AMD relative to late AMD. Several biological processes were suggested to be potentially specific for early AMD, including pathways regulating RPE cell melanin content and signalling pathways potentially involved in retinal regeneration, generating hypotheses for further investigation.

Optimizing the information yield of 3-D OCT in glaucoma

PURPOSE

To determine, first, which regions of 3-D optical coherence tomography (OCT) volumes can be segmented completely in the majority of subjects and, second, the relationship between analyzed area and thickness measurement test-retest variability.

METHODS

Three-dimensional OCT volumes (6 × 6 mm) centered around the fovea and optic nerve head (ONH) of 925 Rotterdam Study participants were analyzed; 44 participants were scanned twice. Volumes were segmented into 10 layers, and we determined the area where all layers could be identified in at least 95% (macula) or 90% (ONH) of subjects. Macular volumes were divided in 2 × 2, 4 × 4, 6 × 6, 8 × 8, or 68 blocks. We placed two circles around the ONH; the ONH had to fit into the smaller circle, and the larger circle had to fit into the segmentable part of the volume. The area between the circles was divided in 3 to 12 segments. We determined the test-retest variability (coefficient of repeatability) of the retinal nerve fiber layer (RNFL) and ganglion cell layer (RGCL) thickness measurements as a function of size of blocks/segments.

RESULTS

Eighty-two percent of the macular volume could be segmented in at least 95% of subjects; for the ONH, this was 65% in at least 90%. The radii of the circles were 1.03 and 1.84 mm. Depending on the analyzed area, median test-retest variability ranged from 8% to 15% for macular RNFL, 11% to 22% for macular RGCL, 5% to 11% for the two together, and 18% to 22% for ONH RNFL.

CONCLUSIONS

Test-retest variability hampers a detailed analysis of 3-D OCT data. Combined macular RNFL and RGCL thickness averaged over larger areas had the best test-retest variability.

Heritability and genome-wide association study to assess genetic differences between advanced age-related macular degeneration subtypes

PURPOSE

To investigate whether the 2 subtypes of advanced age-related macular degeneration (AMD), choroidal neovascularization (CNV), and geographic atrophy (GA) segregate separately in families and to identify which genetic variants are associated with these 2 subtypes.

DESIGN

Sibling correlation study and genome-wide association study (GWAS).

PARTICIPANTS

For the sibling correlation study, 209 sibling pairs with advanced AMD were included. For the GWAS, 2594 participants with advanced AMD subtypes and 4134 controls were included. Replication cohorts included 5383 advanced AMD participants and 15 240 controls.

METHODS

Participants had the AMD grade assigned based on fundus photography, examination, or both. To determine heritability of advanced AMD subtypes, a sibling correlation study was performed. For the GWAS, genome-wide genotyping was conducted and 6 036 699 single nucleotide polymorphisms (SNPs) were imputed. Then, the SNPs were analyzed with a generalized linear model controlling for genotyping platform and genetic ancestry. The most significant associations were evaluated in independent cohorts.

MAIN OUTCOME MEASURES

Concordance of advanced AMD subtypes in sibling pairs and associations between SNPs with GA and CNV advanced AMD subtypes.

RESULTS

The difference between the observed and expected proportion of siblings concordant for the same subtype of advanced AMD was different to a statistically significant degree (P = 4.2 × 10(-5)), meaning that in siblings of probands with CNV or GA, the same advanced subtype is more likely to develop. In the analysis comparing participants with CNV to those with GA, a statistically significant association was observed at the ARMS2/HTRA1 locus (rs10490924; odds ratio [OR], 1.47; P = 4.3 × 10(-9)), which was confirmed in the replication samples (OR, 1.38; P = 7.4 × 10(-14) for combined discovery and replication analysis).

CONCLUSIONS

Whether CNV versus GA develops in a patient with AMD is determined in part by genetic variation. In this large GWAS meta-analysis and replication analysis, the ARMS2/HTRA1 locus confers increased risk for both advanced AMD subtypes, but imparts greater risk for CNV than for GA. This locus explains a small proportion of the excess sibling correlation for advanced AMD subtype. Other loci were detected with suggestive associations that differ for advanced AMD subtypes and deserve follow-up in additional studies.

Large scale international replication and meta-analysis study confirms association of the 15q14 locus with myopia. The CREAM consortium

Myopia is a complex genetic disorder and a common cause of visual impairment among working age adults. Genome-wide association studies have identified susceptibility loci on chromosomes 15q14 and 15q25 in Caucasian populations of European ancestry. Here, we present a confirmation and meta-analysis study in which we assessed whether these two loci are also associated with myopia in other populations. The study population comprised 31 cohorts from the Consortium of Refractive Error and Myopia (CREAM) representing 4 different continents with 55,177 individuals; 42,845 Caucasians and 12,332 Asians. We performed a meta-analysis of 14 single nucleotide polymorphisms (SNPs) on 15q14 and 5 SNPs on 15q25 using linear regression analysis with spherical equivalent as a quantitative outcome, adjusted for age and sex. We calculated the odds ratio (OR) of myopia versus hyperopia for carriers of the top-SNP alleles using a fixed effects meta-analysis. At locus 15q14, all SNPs were significantly replicated, with the lowest P value 3.87 × 10(-12) for SNP rs634990 in Caucasians, and 9.65 × 10(-4) for rs8032019 in Asians. The overall meta-analysis provided P value 9.20 × 10(-23) for the top SNP rs634990. The risk of myopia versus hyperopia was OR 1.88 (95 % CI 1.64, 2.16, P < 0.001) for homozygous carriers of the risk allele at the top SNP rs634990, and OR 1.33 (95 % CI 1.19, 1.49, P < 0.001) for heterozygous carriers. SNPs at locus 15q25 did not replicate significantly (P value 5.81 × 10(-2) for top SNP rs939661). We conclude that common variants at chromosome 15q14 influence susceptibility for myopia in Caucasian and Asian populations world-wide.

Retinopathy and risk of dementia: the Rotterdam Study

OBJECTIVE

To investigate the relation between retinopathy and the risk of dementia.

METHODS

We investigated the associations between retinopathy and dementia and its subtypes Alzheimer disease (AD) and vascular dementia both cross-sectionally and prospectively in the Rotterdam Study, a large population-based cohort study. Digitized retinal images were available for 195 participants with prevalent dementia and 6,078 participants without dementia at baseline (1990-1993). Participants were reexamined in 1993-1994, 1997-1999, and 2002-2004 and were continuously monitored for development of dementia until January 1, 2007. Retinopathy was graded on fundus photographs and was defined as the presence of one or more dot/blot hemorrhages, microaneurysms, cotton wool spots, or evidence of laser treatment for retinopathy.

RESULTS

Retinopathy was associated with prevalent dementia (age and sex-adjusted odds ratio 2.04, 95% confidence interval [CI] 1.34-3.09). Results were similar for AD and vascular dementia. During a mean follow-up of 11.4 years, 735 participants developed incident dementia, of whom 583 had AD and 80 had vascular dementia. There was no association of retinopathy at baseline with the risk of incident dementia during follow-up (age- and sex-adjusted hazard ratio 1.15, 95% CI 0.88-1.48) or the risk of incident AD or vascular dementia.

CONCLUSIONS

Retinopathy is more prevalent in persons with dementia but is not associated with an increased risk of dementia over time.

Antithrombotic medication and incident open-angle glaucoma

PURPOSE

To determine the associations between the use of antithrombotic drugs and incident open-angle glaucoma (OAG).

METHODS

Ophthalmic examinations including measurements of the IOP and perimetry were performed at baseline and follow-up in 3939 participants of the prospective population-based Rotterdam Study who did not have OAG at baseline. The use of antithrombotic drugs was monitored continuously during follow-up. Antithrombotic drugs were stratified into anticoagulants and platelet aggregation inhibitors. Associations between incident OAG and the use of antithrombotic drugs were assessed using Cox regression; the model was adjusted for age, sex, baseline IOP and IOP-lowering treatment, family history of glaucoma, and myopia. Associations between antithrombotic drugs and IOP at follow-up were analyzed with multiple linear regression.

RESULTS

During a mean follow-up of 9.8 years, 108 participants (2.7%) developed OAG. The hazard ratio for anticoagulant use was 0.90 (95% confidence interval [CI], 0.55-1.48; P = 0.69) and for platelet aggregation inhibitors 0.80 (0.53-1.21; P = 0.28). There was no trend towards a reduced or increased risk of incident OAG with prolonged anticoagulant use (P value for trend 0.84) or platelet aggregation inhibitor use (0.59). There was a significant IOP-lowering effect of anticoagulants (-0.31 mm Hg; 95% CI, -0.58 to -0.04 mm Hg; P = 0.025) but not of platelet aggregation inhibitors (P = 0.06). The IOP-lowering effect of anticoagulants disappeared after additional adjustment for the use of systemic beta-blockers.

CONCLUSIONS

Use of anticoagulants or platelet aggregation inhibitors appears not to be associated with incident OAG.

Nutrient intake and risk of open-angle glaucoma: the Rotterdam Study

Open-angle glaucoma (OAG) is the commonest cause of irreversible blindness worldwide. Apart from an increased intraocular pressure (IOP), oxidative stress and an impaired ocular blood flow are supposed to contribute to OAG. The aim of this study was to determine whether the dietary intake of nutrients that either have anti-oxidative properties (carotenoids, vitamins, and flavonoids) or influence the blood flow (omega fatty acids and magnesium) is associated with incident OAG. We investigated this in a prospective population-based cohort, the Rotterdam Study. A total of 3502 participants aged 55 years and older for whom dietary data at baseline and ophthalmic data at baseline and follow-up were available and who did not have OAG at baseline were included. The ophthalmic examinations comprised measurements of the IOP and perimetry; dietary intake of nutrients was assessed by validated questionnaires and adjusted for energy intake. Cox proportional hazard regression analysis was applied to calculate hazard ratios of associations between the baseline intake of nutrients and incident OAG, adjusted for age, gender, IOP, IOP-lowering treatment, and body mass index. During an average follow-up of 9.7 years, 91 participants (2.6%) developed OAG. The hazard ratio for retinol equivalents (highest versus lowest tertile) was 0.45 (95% confidence interval 0.23–0.90), for vitamin B1 0.50 (0.25–0.98), and for magnesium 2.25 (1.16–4.38). The effects were stronger after the exclusion of participants taking supplements. Hence, a low intake of retinol equivalents and vitamin B1 (in line with hypothesis) and a high intake of magnesium (less unambiguous to interpret) appear to be associated with an increased risk of OAG.

A genetic epidemiologic study of candidate genes involved in the optic nerve head morphology

PURPOSE

The size of the optic nerve head, referred to as disc area (DA), and the vertical cup-disc ratio (VCDR), are clinically relevant parameters for glaucomatous optic neuropathy. Although these measures have a high heritability, little is known about the underlying genes. Previously, the genes SALL1 and SIX1 were found to be genome-wide significantly associated with DA and VCDR. The purpose of the present study was to investigate whether genes encoding protein known to interact with protein encoded by SALL1 and SIX1 are also associated with either DA or VCDR.

METHODS

A total of 38 candidate genes were chosen covering all known proteins interacting with SALL1 and SIX1. These were initially studied in the Rotterdam Study (RS)-I, including 5312 Caucasian subjects characterized for DA and VCDR. Positive findings were further investigated in two independent cohorts (RS-II and RS-III) and finally replicated in a fourth population (ERF). Bonferroni correction was applied to the meta-analyses.

RESULTS

Three loci were found to be associated with DA. The only locus significant after correcting for multiple testing is located on chromosome 11p13. Three single nucleotide polymorphisms (SNPs) in ELP4, a gene which neighbors and plays a crucial role in the expression of PAX6, show association in meta-analysis of the four cohorts yielding P values of respectively 4.79 × 10(-6), 3.92 × 10(-6), and 4.88 × 10(-6) which is below the threshold dictated by the most conservative Bonferroni correction (P = 5.2 × 10(-6)).

CONCLUSIONS

This study suggests that the ELP4-PAX6 region plays a role in the DA. Further research to confirm this finding is needed.

Multicenter cohort association study of SLC2A1 single nucleotide polymorphisms and age-related macular degeneration

PURPOSE

Age-related macular degeneration (AMD) is a major cause of blindness in older adults and has a genetically complex background. This study examines the potential association between single nucleotide polymorphisms (SNPs) in the glucose transporter 1 (SLC2A1) gene and AMD. SLC2A1 regulates the bioavailability of glucose in the retinal pigment epithelium (RPE), which might influence oxidative stress-mediated AMD pathology.

METHODS

Twenty-two SNPs spanning the SLC2A1 gene were genotyped in 375 cases and 199 controls from an initial discovery cohort (the Amsterdam-Rotterdam-Netherlands study). Replication testing was performed in The Rotterdam Study (the Netherlands) and study populations from Würzburg (Germany), the Age Related Eye Disease Study (AREDS; United States), Columbia University (United States), and Iowa University (United States). Subsequently, a meta-analysis of SNP association was performed.

RESULTS

In the discovery cohort, significant genotypic association between three SNPs (rs3754219, rs4660687, and rs841853) and AMD was found. Replication in five large independent (Caucasian) cohorts (4,860 cases and 4,004 controls) did not yield consistent association results. The genotype frequencies for these SNPs were significantly different for the controls and/or cases among the six individual populations. Meta-analysis revealed significant heterogeneity of effect between the studies.

CONCLUSIONS

No overall association between SLC2A1 SNPs and AMD was demonstrated. Since the genotype frequencies for the three SLC2A1 SNPs were significantly different for the controls and/or cases between the six cohorts, this study corroborates previous evidence that population dependent genetic risk heterogeneity in AMD exists.

Cholesterol-lowering drugs and incident open-angle glaucoma: a population-based cohort study

Background

Open-angle glaucoma (OAG) is a progressive neurodegenerative disease that may lead to blindness. An elevated intraocular pressure (IOP) is its major risk factor. OAG treatment is currently exclusively directed towards the lowering of the IOP. IOP lowering does not prevent disease progression in all patients and thus other treatment modalities are needed. Earlier studies reported cholesterol-lowering drugs to have neuroprotective properties. The aim of this study was to determine the associations between the use of cholesterol-lowering drugs and incident OAG.

Methodology/Principal Findings

Participants in a prospective population-based cohort study underwent ophthalmic examinations, including IOP measurements and perimetry, at baseline and follow-up. The use of statins and non-statin cholesterol-lowering drugs was monitored continuously during the study. Associations between the use of cholesterol-lowering drugs and incident OAG were analyzed with Cox regression; associations between cholesterol-lowering drugs and IOP at follow-up were analyzed with multiple linear regression. During a mean follow-up of 9.8 years, 108 of 3939 eligible participants (2.7%) developed OAG. The hazard ratio for statin use was 0.54 (95% confidence interval 0.31–0.96; P = 0.034) and for non-statin cholesterol-lowering drugs 2.07 (0.81–5.33; P = 0.13). The effect of statins was more pronounced with prolonged use (hazard ratio 0.89 [0.41–1.94; P = 0.77] for use two years or less; 0.46 [0.23–0.94; P = 0.033] for use more than two years; P-value for trend 0.10). The analyzes were adjusted for age and gender, baseline IOP and IOP-lowering treatment, the family history of glaucoma, and myopia. There was no effect of statins on the IOP.

Conclusions/Significance

Long-term use of statins appears to be associated with a reduced risk of OAG. The observed effect was independent of the IOP. These findings are in line with the idea that statins have neuroprotective properties and may open a way to a new OAG treatment modality.

Heidelberg Retina Tomograph (HRT3) in population-based epidemiology: normative values and criteria for glaucomatous optic neuropathy

PURPOSE

To establish normative values for Heidelberg Retina Tomograph (HRT3) variables and to develop HRT3-based criteria for glaucomatous optic neuropathy for epidemiological research in a white population.

METHODS

Consecutive participants in the Rotterdam Study were examined with HRT and simultaneous stereoscopic fundus photography (ImageNet) in addition to other ophthalmic examinations including intraocular pressure (IOP) measurements and perimetry. Normative values for all HRT3 variables were determined in participants who met all the following criteria: no glaucomatous visual field loss (GVFL), an IOP of 21mmHg or less, no IOP lowering treatment, and a negative family history of glaucoma. Sensitivity was determined in participants with glaucomatous visual field loss at a fixed high specificity of 97.5% - a value commonly used in population-based epidemiology.

RESULTS

A total of 2516 participants were included in this study of whom 66 had glaucomatous visual field loss in at least one eye and 1680 fulfilled the criteria for contributing to the normative values. The HRT3 linear cup-disc ratio (LCDR) variable, adjusted for disc area, showed the highest sensitivity, 35%, at the required specificity of 97.5%. The 97.5th percentile of the LCDR was 0.67 for small discs (up to 1.5 mm(2)), 0.71 [corrected] for medium-sized discs and 0.76 [corrected] for large discs (above 2.0 mm(2)).The HRT3 Glaucoma Probability Score and previously published linear discriminant functions showed a lower sensitivity than LCDR at this specificity.

CONCLUSIONS

At the high specificity of 97.5% as is commonly used in population-based epidemiology, the sensitivity of the HRT3 is low - albeit not lower than that of the vertical cup-disc ratio as assessed with simultaneous stereoscopic fundus photography and analyzed with the ImageNet software. The LCDR variable, stratified for disc area, seems to be the most suitable variable to develop criteria for glaucomatous optic neuropathy for epidemiological purposes.

Defining glaucomatous optic neuropathy from a continuous measure of optic nerve damage - the optimal cut-off point for risk-factor analysis in population-based epidemiology

PURPOSE

Diseases characterized by a continuous trait can be defined by setting a cut-off point for the disease measure in question, accepting some misclassification. The 97.5th percentile is commonly used as a cut-off point. However, it is unclear whether this percentile is the optimal cut-off point from the point of view of risk-factor analysis. The optimal cut-off point for risk-factor analysis can be found with a statistical method that minimizes the effect of misclassification. We applied this method to glaucomatous optic neuropathy. Here, the continuous trait is the cup-disc ratio. The aim of this study was to determine the optimal cup-disc ratio cut-off point for risk-factor analysis in population-based epidemiology.

METHODS

All participants in the population-based Rotterdam Study underwent intraocular pressure (IOP) measurements, assessment of the cup-disc ratio with the Heidelberg Retina Tomograph (HRT) and visual field testing. In the statistical method, the cup-disc ratio (the continuous trait) and the IOP (a major risk factor) were independent variables and glaucomatous visual field loss (the true glaucoma endpoint) the dependent variable in a logistic regression model. The optimal cup-disc ratio cut-off point was found by minimizing the influence of IOP in this model. Variability of the approach was assessed by using a bootstrap resampling technique.

RESULTS

Of 2444 included participants, 93 had glaucomatous visual field loss. The median optimal cup-disc ratio cut-off point was the 97.0th percentile with a 95% central range from 95.5 to 98.5.

CONCLUSION

The optimal cup-disc ratio cut-off point for risk-factor analysis is close to the commonly used 97.5th percentile.

Sifting the wheat from the chaff: prioritizing GWAS results by identifying consistency across analytical methods

The curse of multiple testing has led to the adoption of a stringent Bonferroni threshold for declaring genome-wide statistical significance for any one SNP as standard practice. Although justified in avoiding false positives, this conservative approach has the potential to miss true associations as most studies are drastically underpowered. As an alternative to increasing sample size, we compare results from a typical SNP-by-SNP analysis with three other methods that incorporate regional information in order to boost or dampen an otherwise noisy signal: the haplotype method (Schaid et al. [2002] Am J Hum Genet 70:425-434), the gene-based method (Liu et al. [2010] Am J Hum Genet 87:139-145), and a new method (interaction count) that uses genome-wide screening of pairwise SNP interactions. Using a modestly sized case-control study, we conduct a genome-wide association studies (GWAS) of age-related macular degeneration, and find striking agreement across all methods in regions of known associated variants. We also find strong evidence of novel associated variants in two regions (Chromosome 2p25 and Chromosome 10p15) in which the individual SNP P-values are only suggestive, but where there are very high levels of agreement between all methods. We propose that consistency between different analysis methods may be an alternative to increasingly larger sample sizes in sifting true signals from noise in GWAS.

Linkage and association analyses of glaucoma related traits in a large pedigree from a Dutch genetically isolated population

BACKGROUND

Despite extensive research on the genetic determinants of glaucoma, the genes identified to date explain only a small proportion of cases in the general population.

METHODS

Genome-wide linkage and association analyses of quantitative traits related to glaucoma were performed: intraocular pressure, size and morphology of the optic disc (individual and combined by method of principal components) and thickness of the retinal nerve fibre layer (RNFL), in a large pedigree from a genetically isolated Dutch population.

RESULTS

For the size of the optic disc, the study demonstrated a significant linkage signal (logarithm of odds (LOD)=3.6) at the LRP1B region on chromosome 2q21.2-q22.2 and significant association (p=8.95×10(-12)) with the previously reported CDC7/TGFBR3 locus at 1p22. For parameters describing morphology of the optic disc, the study obtained significant linkage signal (LOD=4.6) at regions SIRPA and RNF24/PANK2 at 20p13 (false discovery rate (FDR) based q value <0.05) and genome-wide significant association (p=2.38×10(-9)) with a common variant in the RERE gene at 1p36. Suggestive linkage and association signals indicated loci for morphology of the optic disc at 2q31-q33 (IGFBP2 locus) and for RNFL thickness at 3p22.2 (DCLK3 locus) and 14q22-q23 (SIX1 locus).

CONCLUSION

This study identified new linkage regions at 20p13 (SIRPA and RNF24/PANK2 loci) and 2q33-q34 (IGFBP2 locus) for parameters describing morphology of the optic disc. The results of the study also suggested common genetic control of these parameters and RNFL thickness by SIX1 and doublecotin family genes. Finally, association signals for the recently reported RERE and LRP1B loci and the well known CDC7, TGFBR3, and ATOH7 loci were replicated.

Visual impairment and quality of life in the older European population, the EUREYE study

PURPOSE

To determine the prevalence of visual impairment (VI) in populations 65 year or older from six European countries and describe the association with vision-related quality of life. VI was defined according to WHO as best corrected visual acuity <6/18/log MAR >0,48 (World Health Organization (1992): International Statistical Classification of Diseases and Related Health Problems, 10th revised ed. Vol 1. Geneva).

METHODS

4166 participants in The European Eye study, 65 years and older selected randomly from the general census in the participating centres, were interviewed for vision-related quality of life and underwent an eye exam including distance visual acuity, refraction and fundus photography.

RESULTS

The prevalence of VI rose with increasing age and more so in women. There was a pattern of a higher prevalence of VI in the Mediterranean countries compared to Northern European countries with the exception of Tallinn (Estonia) which had higher VI prevalence rates than the other north European centres. The prevalence of low vision was 3% or less in all centres. Blindness prevalence varied from 2% to less than half a per cent. Vision-related quality of life was strongly associated with visual acuity and the presence of bilateral age-related macular degeneration.

CONCLUSION

The prevalence of visual impairment in the examined ageing European populations shows a definite increasing trend from north to south.

Evidence of association of APOE with age-related macular degeneration: a pooled analysis of 15 studies

Age-related macular degeneration (AMD) is the most common cause of incurable visual impairment in high-income countries. Previous studies report inconsistent associations between AMD and apolipoprotein E (APOE), a lipid transport protein involved in low-density cholesterol modulation. Potential interaction between APOE and sex, and smoking status has been reported. We present a pooled analysis (n = 21,160) demonstrating associations between late AMD and APOε4 (odds ratio [OR] = 0.72 per haplotype; confidence interval [CI]: 0.65-0.74; P = 4.41×10(-11) ) and APOε2 (OR = 1.83 for homozygote carriers; CI: 1.04-3.23; P = 0.04), following adjustment for age group and sex within each study and smoking status. No evidence of interaction between APOE and sex or smoking was found. Ever smokers had significant increased risk relative to never smokers for both neovascular (OR = 1.54; CI: 1.38-1.72; P = 2.8×10(-15) ) and atrophic (OR = 1.38; CI: 1.18-1.61; P = 3.37×10(-5) ) AMD but not early AMD (OR = 0.94; CI: 0.86-1.03; P = 0.16), implicating smoking as a major contributing factor to disease progression from early signs to the visually disabling late forms. Extended haplotype analysis incorporating rs405509 did not identify additional risks beyond ε2 and ε4 haplotypes. Our expanded analysis substantially improves our understanding of the association between the APOE locus and AMD. It further provides evidence supporting the role of cholesterol modulation, and low-density cholesterol specifically, in AMD disease etiology.

Ocular perfusion pressure and the incidence of glaucoma: real effect or artifact? The Rotterdam Study

PURPOSE

To determine the association between the ocular perfusion pressure (OPP; essentially the difference between the blood pressure and the intraocular pressure [IOP]) and incident open-angle glaucoma (OAG).

METHODS

A subset of 3882 participants of the population-based Rotterdam Study for whom data from ophthalmic examinations at baseline and follow-up and blood pressure measurements at baseline were available, and who did not have OAG at baseline, were included. Associations between the mean, systolic and diastolic OPP, and incident OAG were assessed using Cox regression models adjusted for age and sex, with and without adjustment for IOP.

RESULTS

During a mean follow-up of 9.8 years, 103 participants (2.7%) developed OAG. The association between the mean OPP and incident OAG was not significant (hazard ratio 0.995 per mm Hg increase in mean OPP; 95% confidence interval 0.971-1.019) when adjusted for IOP, but became significant if not adjusted for IOP (0.968; 0.945-0.992). The systolic and diastolic OPP showed a pattern similar to that of the mean OPP, though less significant.

CONCLUSIONS

The OPP appears to be associated with incident OAG but this association seems to be due to the fact that the IOP, a strong risk factor for OAG, is part of the OPP, rather than that OPP is an independent OAG risk factor itself.

Clinical implications of old and new genes for open-angle glaucoma

OBJECTIVE

Genome-wide association studies have revealed new insights into the genetic determinants of open-angle glaucoma (OAG). This study was performed to determine to what extent variants within established genes (MYOC, OPTN, and WDR36) and newly identified common genetic variants (ATOH7, CDKN2B, and SIX1) contribute to the risk of OAG.

DESIGN

Population-based setting, family-based setting, and a case-control study.

PARTICIPANTS

The Rotterdam Study I cohort (N = 5312; mean age±standard deviation [SD], 68.0±8.4 years). Findings were replicated in the Genetic Research in Isolated Populations combined with the Erasmus Rucphen Family study (N = 1750; mean age±SD, 48.3±15.2 years), and a cohort from Southampton (N = 702; mean age±SD, 72.5±10.7 years).

METHODS

After identifying common variants associated with OAG within the established genes, the risk of OAG was analyzed using logistic regression. Discriminative accuracy was assessed by comparing the area under the receiver operator characteristic curve (AUC) for models, including the number of risk alleles, intraocular pressure, age, and gender, with the AUC for the same model but without the risk alleles.

MAIN OUTCOME MEASURES

Odds ratios and AUCs of individual and combined risk alleles.

RESULTS

No consistent significant associations for the established genes (MYOC, OPTN, and WDR36) with OAG were found. However, when comparing the load of risk variants between cases and controls, 2 of 3 studies showed a significant increased risk of OAG for participants carrying more risk alleles of the 3 established genes. When combining all 6 genes, participants carrying a high number of risk alleles (highest tertile) had a 2.29-fold to 3.19-fold increase in risk of OAG compared with those carrying only a few risk alleles. The addition of the newly identified genes to IOP, age, and gender resulted in a higher AUC compared with the AUC without the newly identified genes (P = 0.027).

CONCLUSIONS

A significant contribution to the risk of OAG was found for the new common variants identified by recent genome-wide association studies, but not for variants within the established genes. Participants carrying a high number of risk alleles had an approximately 3-fold increase in the risk of OAG compared with those with a low number of risk alleles.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Reducing the genetic risk of age-related macular degeneration with dietary antioxidants, zinc, and ω-3 fatty acids: the Rotterdam study

OBJECTIVE

To investigate whether dietary nutrients can reduce the genetic risk of early age-related macular degeneration (AMD) conferred by the genetic variants CFH Y402H and LOC387715 A69S in a nested case-control study.

METHODS

For 2167 individuals (≥55 years) from the population-based Rotterdam Study at risk of AMD, dietary intake was assessed at baseline using a semiquantitative food frequency questionnaire and genetic variants were determined using TaqMan assay. Incident early AMD was determined on fundus photographs at 3 follow-up visits (median follow-up, 8.6 years). The synergy index was used to evaluate biological interaction between risk factors; hazard ratios were calculated to estimate risk of early AMD in strata of nutrient intake and genotypes.

RESULTS

Five hundred seventeen participants developed early AMD. Significant synergy indices supported the possibility of biological interaction between CFH Y402H and zinc, β-carotene, lutein/zeaxanthin, and eicosapentaenoic/docosahexaenoic acid (EPA/DHA) and between LOC387715 A69S and zinc and EPA/DHA (all P < .05). Homozygotes of CFH Y402H with dietary intake of zinc in the highest tertile reduced their hazard ratio of early AMD from 2.25 to 1.27. For intakes of β-carotene, lutein/zeaxanthin, and EPA/DHA, these risk reductions were from 2.54 to 1.47, 2.63 to 1.72, and 1.97 to 1.30, respectively. Carriers of LOC387715 A69S with the highest intake of zinc and EPA/DHA reduced their risk from 1.70 to 1.17 and 1.59 to 0.95, respectively (all P trends <.05).

CONCLUSIONS

High dietary intake of nutrients with antioxidant properties reduces the risk of early AMD in those at high genetic risk. Therefore, clinicians should provide dietary advice to young susceptible individuals to postpone or prevent the vision-disabling consequences of AMD.

DNA-based eye colour prediction across Europe with the IrisPlex system

The ability to predict Externally Visible Characteristics (EVCs) from DNA, also referred to as Forensic DNA Phenotyping (FDP), is an exciting new chapter in forensic genetics holding great promise for tracing unknown individuals who are unidentifiable via standard forensic short tandem repeat (STR) profiling. For the purpose of DNA-based eye colour prediction, we previously developed the IrisPlex system consisting of a multiplex genotyping assay and a prediction model based on genotype and phenotype data from 3804 Dutch Europeans. Recently, we performed a forensic developmental validation study of the highly sensitive IrisPlex assay, which currently represents the only validated tool available for DNA-based prediction of eye colour in forensic applications. In the present study, we validate the IrisPlex prediction model by extending our initially described model towards genotype and phenotype data from multiple European populations. We performed IrisPlex analysis on 3840 individuals from seven sites across Europe as part of the European Eye (EUREYE) study for which DNA and high-resolution eye images were available. The accuracy rate of correctly predicting an individual's eye colour as being blue or brown, above the empirically established probability threshold of 0.7, was on average 94% across all seven European populations, ranging from 91% to 98%, despite the large variation in eye colour frequencies between the populations. The overall prediction accuracies expressed by the area under the receiver characteristic operating curves (AUC) were 0.96 for blue and 0.96 for brown eyes, which is considerably higher than those established before. The IrisPlex prediction model parameters generated from this multi-population European dataset, and thus its prediction capabilities, were highly comparable to those previously established. Therefore, the increased information regarding eye colour phenotype and genotype distributions across Europe, and the system's ability to provide eye colour predictions across Europe accurately, both highlight additional evidence for the utility of the IrisPlex system in forensic casework.

Automated 3-D method for the correction of axial artifacts in spectral-domain optical coherence tomography images

The 3-D spectral-domain optical coherence tomography (SD-OCT) images of the retina often do not reflect the true shape of the retina and are distorted differently along the x and y axes. In this paper, we propose a novel technique that uses thin-plate splines in two stages to estimate and correct the distinct axial artifacts in SD-OCT images. The method was quantitatively validated using nine pairs of OCT scans obtained with orthogonal fast-scanning axes, where a segmented surface was compared after both datasets had been corrected. The mean unsigned difference computed between the locations of this artifact-corrected surface after the single-spline and dual-spline correction was 23.36 ± 4.04 μm and 5.94 ± 1.09 μm, respectively, and showed a significant difference (p < 0.001 from two-tailed paired t-test). The method was also validated using depth maps constructed from stereo fundus photographs of the optic nerve head, which were compared to the flattened top surface from the OCT datasets. Significant differences (p < 0.001) were noted between the artifact-corrected datasets and the original datasets, where the mean unsigned differences computed over 30 optic-nerve-head-centered scans (in normalized units) were 0.134 ± 0.035 and 0.302 ± 0.134, respectively.

Variations in apolipoprotein E frequency with age in a pooled analysis of a large group of older people

Variation in the apolipoprotein E gene (APOE) has been reported to be associated with longevity in humans. The authors assessed the allelic distribution of APOE isoforms ε2, ε3, and ε4 among 10,623 participants from 15 case-control and cohort studies of age-related macular degeneration (AMD) in populations of European ancestry (study dates ranged from 1990 to 2009). The authors included only the 10,623 control subjects from these studies who were classified as having no evidence of AMD, since variation within the APOE gene has previously been associated with AMD. In an analysis stratified by study center, gender, and smoking status, there was a decreasing frequency of the APOE ε4 isoform with increasing age (χ(2) for trend = 14.9 (1 df); P = 0.0001), with a concomitant increase in the ε3 isoform (χ(2) for trend = 11.3 (1 df); P = 0.001). The association with age was strongest in ε4 homozygotes; the frequency of ε4 homozygosity decreased from 2.7% for participants aged 60 years or less to 0.8% for those over age 85 years, while the proportion of participants with the ε3/ε4 genotype decreased from 26.8% to 17.5% across the same age range. Gender had no significant effect on the isoform frequencies. This study provides strong support for an association of the APOE gene with human longevity.

Common variants near FRK/COL10A1 and VEGFA are associated with advanced age-related macular degeneration

Despite significant progress in the identification of genetic loci for age-related macular degeneration (AMD), not all of the heritability has been explained. To identify variants which contribute to the remaining genetic susceptibility, we performed the largest meta-analysis of genome-wide association studies to date for advanced AMD. We imputed 6 036 699 single-nucleotide polymorphisms with the 1000 Genomes Project reference genotypes on 2594 cases and 4134 controls with follow-up replication of top signals in 5640 cases and 52 174 controls. We identified two new common susceptibility alleles, rs1999930 on 6q21-q22.3 near FRK/COL10A1 [odds ratio (OR) 0.87; P = 1.1 × 10⁻⁸] and rs4711751 on 6p12 near VEGFA (OR 1.15; P = 8.7 × 10⁻⁹). In addition to the two novel loci, 10 previously reported loci in ARMS2/HTRA1 (rs10490924), CFH (rs1061170, and rs1410996), CFB (rs641153), C3 (rs2230199), C2 (rs9332739), CFI (rs10033900), LIPC (rs10468017), TIMP3 (rs9621532) and CETP (rs3764261) were confirmed with genome-wide significant signals in this large study. Loci in the recently reported genes ABCA1 and COL8A1 were also detected with suggestive evidence of association with advanced AMD. The novel variants identified in this study suggest that angiogenesis (VEGFA) and extracellular collagen matrix (FRK/COL10A1) pathways contribute to the development of advanced AMD.

Common genetic variants associated with open-angle glaucoma

Open-angle glaucoma (glaucoma) is a major eye disorder characterized by optic disc pathology. Recent genome-wide association studies identified new loci associated with clinically relevant optic disc parameters, such as the optic disc area and vertical cup-disc ratio (VCDR). We examined to what extent these loci are involved in glaucoma. The loci studied include ATOH7, CDC7/TGFBR3 and SALL1 for optic disc area, and CDKN2B, SIX1, SCYL1/LTBP3, CHEK2, ATOH7 and DCLK1 for VCDR. We performed a meta-analysis using data from six independent studies including: the Rotterdam Study (n= 5736), Genetic Research in Isolated Populations combined with Erasmus Rucphen Family study (n= 1750), Amsterdam Glaucoma Study (n= 296) and cohorts from Erlangen and Tübingen (n= 1363), Southampton (n= 702) and deCODE (n= 36 151) resulting in a total of 3161 glaucoma cases and 42 837 controls. Of the eight loci, we found significant evidence (P= 1.41 × 10(-8)) for the association of CDKN2B with glaucoma [odds ratio (OR) for those homozygous for the risk allele: 0.76; 95% confidence interval (CI): 0.70-0.84], for the role of ATOH7 (OR: 1.28; 95% CI: 1.12-1.47) and for SIX1 (OR: 1.20; 95% CI: 1.10-1.31) when adjusting for the number of tested loci. Furthermore, there was a borderline significant association of CDC7/TGFBR3 and SALL1 (both P= 0.04) with glaucoma. In conclusion, we found consistent evidence for three common variants (CDKN2B, ATOH7 and SIX1) significantly associated with glaucoma. These findings may shed new light on the pathophysiological protein pathways leading to glaucoma, and point to pathways involved in the growth and development of the optic nerve.

Lifestyle and risk of developing open-angle glaucoma: the Rotterdam study

OBJECTIVE

To determine whether lifestyle-related risk factors, such as socioeconomic status, smoking, alcohol consumption, and obesity, are associated with open-angle glaucoma (OAG).

METHODS

Participants from the Rotterdam Study, a prospective population-based cohort study, were considered eligible if they participated at both baseline and follow-up and if they had no OAG at baseline. All participants underwent an identical ophthalmologic examination at all visits, including intraocular pressure measurements, optic nerve head assessment, and perimetry. Lifestyle-related factors were assessed by questionnaires by trained research assistants or measured during the examinations (body mass index and waist to hip ratio). Cox proportional hazard regression analysis was applied to calculate hazard ratios.

RESULTS

Of 3939 eligible participants, 108 (2.7%) developed OAG during 9.7 years' mean follow-up. No statistically significant effect of socioeconomic status, smoking, or alcohol intake was found. In women, each unit increase in body mass index resulted in a 7% decrease in the risk of developing OAG (P = .04). There was a significant increasing effect of body mass index on intraocular pressure (P < .001) in women.

CONCLUSIONS

Obesity appears to be associated with a higher intraocular pressure and a lower risk of developing OAG. These associations were only present in women. Other lifestyle-related factors, such as socioeconomic status, smoking, and alcohol consumption, were not associated with OAG.

Genome-wide association studies in Asians confirm the involvement of ATOH7 and TGFBR3, and further identify CARD10 as a novel locus influencing optic disc area

Damage to the optic nerve (e.g. from glaucoma) has an adverse and often irreversible impact on vision. Earlier studies have suggested that the size of the optic nerve head could be governed by hereditary factors. We conducted a genome-wide association study (GWAS) on 4445 Singaporean individuals (n = 2132 of Indian and n = 2313 of Malay ancestry, respectively), with replication in Rotterdam, the Netherlands (n = 9326 individuals of Caucasian ancestry) using the most widely reported parameter for optic disc traits, the optic disc area. We identified a novel locus on chromosome 22q13.1, CARD10, which strongly associates with optic disc area in both Singaporean cohorts as well as in the Rotterdam Study (RS; rs9607469, per-allele change in optic disc area = 0.051 mm(2); P(meta) = 2.73×10(-12)) and confirmed the association between CDC7/TGFBR3 (lead single nucleotide polymorphism (SNP) rs1192415, P(meta) = 7.57×10(-17)) and ATOH7 (lead SNP rs7916697, P(meta) = 2.00 × 10(-15)) and optic disc area in Asians. This is the first Asian-based GWAS on optic disc area, identifying a novel locus for the optic disc area, but also confirming the results found in Caucasian persons suggesting that there are general genetic determinants applicable to the size of the optic disc across different ethnicities.

Retinal vascular caliber and risk of dementia: the Rotterdam study

BACKGROUND

Retinal vessels provide a unique opportunity to study both systemic and cerebrovascular disease. Smaller retinal arteriolar calibers are strongly related to hypertension, whereas larger retinal venular calibers are more related to inflammation, cerebral hypoperfusion, and cerebrovascular disease. Whether retinal vessel calibers are related to dementia remains unclear.

METHODS

We investigated whether retinal arteriolar and venular calibers are associated with risk of dementia, and its subtypes Alzheimer disease (AD) and vascular dementia, in the prospective population-based Rotterdam Study. Digitized retinal images were available in 5,553 participants aged 55 years or over and dementia-free at baseline (1990-1993). Participants were re-examined in 1993-1994, 1997-1999, and 2002-2004 and were continuously monitored for development of dementia.

RESULTS

During a mean follow-up of 11.6 years, 655 participants developed dementia. AD was diagnosed in 519 and vascular dementia in 73 participants. Larger venular calibers were associated with an increased risk of dementia, in particular vascular dementia (age- and sex-adjusted hazard ratio per SD increase: 1.31; 95% confidence interval 1.06-1.64), but not AD. The association remained significant after adjustment for stroke and cardiovascular risk factors. Smaller arteriolar calibers were also associated with an increased risk of vascular dementia, yet only when adjusted for venular calibers.

CONCLUSIONS

Retinal venular widening is associated with an increased risk of vascular dementia. Our findings are in line with previous observations in stroke and cerebral small-vessel disease and suggest that the association between larger retinal venular calibers and dementia may reflect cerebral hypoperfusion and subsequent ischemia.

Genetic architecture of open angle glaucoma and related determinants

BACKGROUND

Although the vertical cup-disc ratio (VCDR) and intraocular pressure (IOP) are important determinants of open angle glaucoma (OAG), it is unclear to what extent the genetic origin of these traits overlap with those of OAG. We evaluated whether the same genes that determine VCDR and IOP also predict OAG.

METHODS

Genetic risk scores were constructed from single nucleotide polymorphisms (SNPs) using genome wide association data of 9326 participants from the Rotterdam Study cohorts (mean ± SD age: 64.6 ± 9.1 years). These risk scores were used to calculate the explained variance of VCDR and IOP in an independent cohort (Erasmus Rucphen Family study) consisting of 1646 participants (mean ± SD age: 46.8 ± 14.1 years) and the OAG risk in a subset of the Rotterdam Study cohorts. To evaluate false positive findings, we generated two new variables containing randomly sampled values to serve as a negative control.

RESULTS

The explained variance of VCDR increased when increasing the number of SNPs included in the risk score, suggesting a polygenic model. We found no clear evidence for a similar model for IOP, suggesting that a small number of SNPs determine the susceptibility to IOP. The SNPs related to IOP in terms of p values contributed little to VCDR. The risk scores associated with VCDR were also associated significantly with OAG. This suggests a common polygenic background for VCDR and OAG CONCLUSIONS: We found evidence for a polygenic model underlying one of the major traits of OAG, VCDR, and OAG itself. The IOP did not show any evidence for such a model.

The ERCC6 gene and age-related macular degeneration

Background

Age-related macular degeneration (AMD) is the leading cause of irreversible visual loss in the developed countries and is caused by both environmental and genetic factors. A recent study (Tuo et al., PNAS) reported an association between AMD and a single nucleotide polymorphism (SNP) (rs3793784) in the ERCC6 (NM_000124) gene. The risk allele also increased ERCC6 expression. ERCC6 is involved in DNA repair and mutations in ERCC6 cause Cockayne syndrome (CS). Amongst others, photosensitivity and pigmentary retinopathy are hallmarks of CS.

Methodology/Principal Findings

Separate and combined data from three large AMD case-control studies and a prospective population-based study (The Rotterdam Study) were used to analyse the genetic association between ERCC6 and AMD (2682 AMD cases and 3152 controls). We also measured ERCC6 mRNA levels in retinal pigment epithelium (RPE) cells of healthy and early AMD affected human donor eyes. Rs3793784 conferred a small increase in risk for late AMD in the Dutch population (The Rotterdam and AMRO-NL study), but this was not replicated in two non-European studies (AREDS, Columbia University). In addition, the AMRO-NL study revealed no significant association for 9 other variants spanning ERCC6. Finally, we determined that ERCC6 expression in the human RPE did not depend on rs3793784 genotype, but, interestingly, on AMD status: Early AMD-affected donor eyes had a 50% lower ERCC6 expression than healthy donor eyes (P = 0.018).

Conclusions/Significance

Our meta-analysis of four Caucasian cohorts does not replicate the reported association between SNPs in ERCC6 and AMD. Nevertheless, our findings on ERCC6 expression in the RPE suggest that ERCC6 may be functionally involved in AMD. Combining our data with those of the literature, we hypothesize that the AMD-related reduced transcriptional activity of ERCC6 may be caused by diverse, small and heterogeneous genetic and/or environmental determinants.

Four novel Loci (19q13, 6q24, 12q24, and 5q14) influence the microcirculation in vivo

There is increasing evidence that the microcirculation plays an important role in the pathogenesis of cardiovascular diseases. Changes in retinal vascular caliber reflect early microvascular disease and predict incident cardiovascular events. We performed a genome-wide association study to identify genetic variants associated with retinal vascular caliber. We analyzed data from four population-based discovery cohorts with 15,358 unrelated Caucasian individuals, who are members of the Cohort for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium, and replicated findings in four independent Caucasian cohorts (n = 6,652). All participants had retinal photography and retinal arteriolar and venular caliber measured from computer software. In the discovery cohorts, 179 single nucleotide polymorphisms (SNP) spread across five loci were significantly associated (p<5.0×10⁻⁸) with retinal venular caliber, but none showed association with arteriolar caliber. Collectively, these five loci explain 1.0%–3.2% of the variation in retinal venular caliber. Four out of these five loci were confirmed in independent replication samples. In the combined analyses, the top SNPs at each locus were: rs2287921 (19q13; p = 1.61×10⁻²⁵, within the RASIP1 locus), rs225717 (6q24; p = 1.25×10⁻¹⁶, adjacent to the VTA1 and NMBR loci), rs10774625 (12q24; p = 2.15×10⁻¹³, in the region of ATXN2,SH2B3 and PTPN11 loci), and rs17421627 (5q14; p = 7.32×10⁻¹⁶, adjacent to the MEF2C locus). In two independent samples, locus 12q24 was also associated with coronary heart disease and hypertension. Our population-based genome-wide association study demonstrates four novel loci associated with retinal venular caliber, an endophenotype of the microcirculation associated with clinical cardiovascular disease. These data provide further insights into the contribution and biological mechanisms of microcirculatory changes that underlie cardiovascular disease.

The microcirculation plays an important role in the development of cardiovascular diseases. Retinal vascular caliber changes reflect early microvascular disease and predict incident cardiovascular events. In order to identify genetic variants associated with retinal vascular caliber, we performed a genome-wide association study and analyzed data from four population-based discovery cohorts with 15,358 unrelated Caucasian individuals, who are members of the Cohort for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium, and replicated findings in four independent Caucasian cohorts (n = 6,652). We found evidence for association of four loci with retinal venular caliber: on chromosomes 19q13 within the RASIP1 locus, 6q24 adjacent to the VTA1 and NMBR loci, 12q24 in the region of ATXN2,SH2B3 and PTPN11 loci, and 5q14 adjacent to the MEF2C locus. In two independent samples, locus 12q24 was also associated with coronary heart disease and hypertension. In the present study, we demonstrate that four novel loci were associated with retinal venular caliber, an endophenotype of the microcirculation associated with clinical cardiovascular disease. Our findings will help focus research on novel genes and pathways involving the microcirculation and its role in the development of cardiovascular disease.

Retinal vascular calibers and the risk of intracerebral hemorrhage and cerebral infarction: the Rotterdam Study

BACKGROUND AND PURPOSE

Narrower retinal arteriolar calibers and wider venular calibers are associated with cardiovascular disease, including cerebral infarction. We investigated the association between retinal vascular calibers and the long-term risk for stroke and its subtypes with particular focus on intracerebral hemorrhage.

METHODS

We included 5518 participants (aged ≥ 55 years) from the prospective population-based Rotterdam Study who were stroke-free at baseline (1990-1993) and of whom digital retinal images were available. Follow-up for incident stroke was complete up to January 1, 2007. Data were analyzed with Cox proportional hazards models adjusted for age and sex and additionally for potential confounders. Arteriolar and venular calibers were entered both separately and simultaneously in the models.

RESULTS

During an average follow-up of 11.5 years, 623 participants developed a first-ever stroke (50 hemorrhagic, 361 ischemic, 212 unspecified). Larger venular caliber was independently associated with an increased risk for stroke (hazard ratio [HR] per SD increase: 1.20; 95% confidence interval [CI]: 1.09 to 1.33), cerebral infarction (HR: 1.28; 95% CI: 1.13 to 1.46), and intracerebral hemorrhage (HR: 1.53; 95% CI: 1.09 to 2.15). Much weaker, only borderline significant associations were found between arteriolar caliber and risk for stroke (HR per SD decrease: 1.12; 95% CI: 0.99 to 1.23), cerebral infarction (HR: 1.12; 95% CI, 0.98 to 1.27), and intracerebral hemorrhage (HR: 1.25; 95% CI: 0.87 to 1.79). Retinal vascular calibers were strongly associated with lobar hemorrhages and oral anticoagulant-related hemorrhages.

CONCLUSIONS

Larger retinal venular caliber is associated with an increased risk for stroke in the general population and, in particular, with an increased risk for intracerebral hemorrhage.

A genome-wide association study identifies a susceptibility locus for refractive errors and myopia at 15q14

Refractive errors are the most common ocular disorders worldwide and may lead to blindness. Although this trait is highly heritable, identification of susceptibility genes has been challenging. We conducted a genome-wide association study for refractive error in 5,328 individuals from a Dutch population-based study with replication in four independent cohorts (combined 10,280 individuals in the replication stage). We identified a significant association at chromosome 15q14 (rs634990, P = 2.21 × 10⁻¹⁴). The odds ratio of myopia compared to hyperopia for the minor allele (minor allele frequency = 0.47) was 1.41 (95% CI 1.16-1.70) for individuals heterozygous for the allele and 1.83 (95% CI 1.42-2.36) for individuals homozygous for the allele. The associated locus is near two genes that are expressed in the retina, GJD2 and ACTC1, and appears to harbor regulatory elements which may influence transcription of these genes. Our data suggest that common variants at 15q14 influence susceptibility for refractive errors in the general population.

A genome-wide association study for myopia and refractive error identifies a susceptibility locus at 15q25

Myopia and hyperopia are at opposite ends of the continuum of refraction, the measure of the eye's ability to focus light, which is an important cause of visual impairment (when aberrant) and is a highly heritable trait. We conducted a genome-wide association study for refractive error in 4,270 individuals from the TwinsUK cohort. We identified SNPs on 15q25 associated with refractive error (rs8027411, P = 7.91 × 10⁻⁸). We replicated this association in six adult cohorts of European ancestry with a combined 13,414 individuals (combined P = 2.07 × 10⁻⁹). This locus overlaps the transcription initiation site of RASGRF1, which is highly expressed in neurons and retina and has previously been implicated in retinal function and memory consolidation. Rasgrf1(-/-) mice show a heavier average crystalline lens (P = 0.001). The identification of a susceptibility locus for refractive error on 15q25 will be important in characterizing the molecular mechanism responsible for the most common cause of visual impairment.

A genome-wide association study of optic disc parameters

The optic nerve head is involved in many ophthalmic disorders, including common diseases such as myopia and open-angle glaucoma. Two of the most important parameters are the size of the optic disc area and the vertical cup-disc ratio (VCDR). Both are highly heritable but genetically largely undetermined. We performed a meta-analysis of genome-wide association (GWA) data to identify genetic variants associated with optic disc area and VCDR. The gene discovery included 7,360 unrelated individuals from the population-based Rotterdam Study I and Rotterdam Study II cohorts. These cohorts revealed two genome-wide significant loci for optic disc area, rs1192415 on chromosome 1p22 (p = 6.72×10⁻¹⁹) within 117 kb of the CDC7 gene and rs1900004 on chromosome 10q21.3-q22.1 (p = 2.67×10⁻³³) within 10 kb of the ATOH7 gene. They revealed two genome-wide significant loci for VCDR, rs1063192 on chromosome 9p21 (p = 6.15×10⁻¹¹) in the CDKN2B gene and rs10483727 on chromosome 14q22.3-q23 (p = 2.93×10⁻¹⁰) within 40 kbp of the SIX1 gene. Findings were replicated in two independent Dutch cohorts (Rotterdam Study III and Erasmus Rucphen Family study; N = 3,612), and the TwinsUK cohort (N = 843). Meta-analysis with the replication cohorts confirmed the four loci and revealed a third locus at 16q12.1 associated with optic disc area, and four other loci at 11q13, 13q13, 17q23 (borderline significant), and 22q12.1 for VCDR. ATOH7 was also associated with VCDR independent of optic disc area. Three of the loci were marginally associated with open-angle glaucoma. The protein pathways in which the loci of optic disc area are involved overlap with those identified for VCDR, suggesting a common genetic origin.

Morphologic characteristics of the optic nerve head are involved in many ophthalmic diseases. Its size, called the optic disc area, is an important measure and has been associated with e.g. myopia and open-angle glaucoma (OAG). Another important and clinical parameter of the optic disc is the vertical cup-disc ratio (VCDR). Although studies have shown a high heritability of optic disc area and VCDR, its genetic determinants are still undetermined. We therefore conducted a genome-wide association (GWA) study on these quantitative traits, using data of over 11,000 Caucasian participants, and related the findings to myopia and OAG. We found evidence for association of three loci with optic disc area: CDC7/TGFBR3 region, ATOH7, and SALL1; and six with VCDR: CDKN2B, SIX1, SCYL1, CHEK2, ATOH7, and DCLK1; and additionally one borderline significant locus: BCAS3. None of the loci could be related to myopia. There was marginal evidence for association of ATOH7, CDKN2B, and SIX1 with OAG, which remains to be confirmed. The present study reveals new insights into the physiological development of the optic nerve and may shed light on the pathophysiological protein pathways leading to (neuro-) ophthalmologic diseases such as OAG.

Digital quantification of human eye color highlights genetic association of three new loci

Previous studies have successfully identified genetic variants in several genes associated with human iris (eye) color; however, they all used simplified categorical trait information. Here, we quantified continuous eye color variation into hue and saturation values using high-resolution digital full-eye photographs and conducted a genome-wide association study on 5,951 Dutch Europeans from the Rotterdam Study. Three new regions, 1q42.3, 17q25.3, and 21q22.13, were highlighted meeting the criterion for genome-wide statistically significant association. The latter two loci were replicated in 2,261 individuals from the UK and in 1,282 from Australia. The LYST gene at 1q42.3 and the DSCR9 gene at 21q22.13 serve as promising functional candidates. A model for predicting quantitative eye colors explained over 50% of trait variance in the Rotterdam Study. Over all our data exemplify that fine phenotyping is a useful strategy for finding genes involved in human complex traits.

We measured human eye color to hue and saturation values from high-resolution, digital, full-eye photographs of several thousand Dutch Europeans. This quantitative approach, which is extremely cost-effective, portable, and time efficient, revealed that human eye color varies along more dimensions than the one represented by the blue-green-brown categories studied previously. Our work represents the first genome-wide study of quantitative human eye color. We clearly identified 3 new loci, LYST, 17q25.3, TTC3/DSCR9, in contributing to the natural and subtle eye color variation along multiple dimensions, providing new leads towards a more detailed understanding of the genetic basis of human eye color. Our quantitative prediction model explained over 50% of eye color variance, representing the highest accuracy achieved so far in genomic prediction of human complex and quantitative traits, with relevance for future forensic applications.