Heritability and shared environment estimates for myopia and associated ocular biometric traits: the Genes in Myopia (GEM) family study

Global prevalence of myopia in children using digital devices: a systematic review and meta-analysis

BACKGROUND

The global prevalence of myopia among children has considerably increased over the past few decades, affecting the children's eye health and quality of life. According to the inconsistent reports of myopia among children, the purpose of this systematic review and meta-analysis study was to determine the global prevalence of myopia in children using digital devices.

METHODS

Various databases (PubMed, ScienceDirect, Embase, Web of Science, Scopus, and Google Scholar) were searched systematically (No time limit until September 2023, last updated in May 2024) using keywords of "Myopia Prevalence", "Children", "TV", "Computer", "Video games", and "Smartphone". PRISMA guideline was also used for paper collection based on the Inclusion/Exclusion criteria. The quality of articles was determined based on the STROBE checklist. Data analysis, heterogeneity assessment, publication bias, and all factors influencing heterogeneity were executed using the CMA software (v.2).

RESULTS

Initially, 828 articles were identified through database assessment. 563 and 133 papers were evaluated using primary and secondary assessments, respectively. Ultimately, 17 eligible articles were selected for meta-analysis following paper exclusion. In this era, the global prevalence of myopia among children using computer and video games was reported 28.8% (95%CI:21.1-38), using TV (TV watching) was 35.4% (95%CI:20.6-53.7), and smartphone usage was 31.4% (95%CI:13.5-57.3).

CONCLUSION

Myopia is now recognized as a critical global issue with a daily increasing rate. Technology, along with various digital devices, causes several issues in this era. It is suggested that the application of all digital screens and smart devices can potentially increase the risk of myopia among children. Thus, the reduction of these smart device applications in children can alleviate the potential risk of myopia. The results of this study can be a guide for health policymakers and a useful advertisement for society and families in paying attention to this problem in children, as well as increasing health interventions such as early screening and timely diagnosis for treatment. In this regard, it can be effective in both prevention and increasing the quality of life of children.

Exploring Molecular Pathways in Refractive Errors Associated with Inherited Retinal Dystrophies

The term inherited retinal dystrophies (IRDs) refers to a diverse range of conditions characterized by retinal dysfunction, and mostly deterioration, leading to a gradual decay of the visual function and eventually to total vision loss. IRDs have a global impact on about 1 in every 3000 to 4000 individuals. However, the prevalence statistics might differ significantly depending on the exact type of dystrophy and the demographic being examined. The cellular pathophysiology and genetic foundation of IRDs have been extensively studied, however, knowledge regarding associated refractive errors remain limited. This review aims to clarify the cellular and molecular processes that underlie refractive errors in IRDs. We did a thorough search of the current literature (Pubmed, accession Feb 2024), selecting works describing phenotypic differences among genes-related to IRDs, particularly in relation to refractive errors. First, we summarize the wide range of IRDs and their genetic causes, describing the genes and biological pathways connected to the etiology of the disease. We then explore the complex relationship between refractive errors and retinal dysfunction, including how the impairment of the vision-related mechanisms in the retina can affect ocular biometry and optical characteristics. New data about the involvement of aberrant signaling pathways, photoreceptor degeneration, and dysfunctional retinal pigment epithelium (RPE) in the development of refractive errors in IRDs have been examined. We also discuss the therapeutic implications of refractive defects in individuals with IRD, including possible approaches to treating visual impairments. In addition, we address the value of using cutting-edge imaging methods and animal models to examine refractive errors linked to IRDs and suggest future lines of inquiry for identifying new targets for treatment. In summary, this study presents an integrated understanding of the cellular and molecular mechanisms underlying refractive errors in IRDs. It illuminates the intricacies of ocular phenotypes in these conditions and offers a tool for understanding mechanisms underlying isolated refractive errors, besides the IRD-related forms.

Heritability and Genetic Factors of Astigmatism and Corneal Curvature: A Systematic Review and Meta-analysis

PURPOSE

To systematically review and meta-analyze all reported heritability studies of refractive astigmatism (RA), corneal astigmatism (CA) and corneal curvature (CC), and evaluate the existing genetic associations of RA, CA and CC.

DESIGN

Systematic review and meta-analysis (PROSPERO ID: CRD42023447370).

METHODS

Studies that reported the heritability and genetic associations of RA, CA and/or CC were identified from PubMed, Web of Science and EMBASE (from inception to October 1, 2023). Newcastle-Ottawa Scale criteria was used to assess the risk of bias. Meta-analyses of heritability were conducted using random-effects model for mean difference. All current genetic associations were catalogued according to level of statistical significance.

RESULTS

Pooled heritabilities were moderate for RA (h2 = 0.46, 95% CI: 0.27-0.65), CA (h2 = 0.48, 95% CI: 0.38-0.58) and CC (h2 = 0.64, 95% CI: 0.53-0.76). Subgroup analyses revealed significant differences between analysis methods (CA: P < .01; CC: P = .03) and populations (CA: P < .01; CC: P < .01) in both CA and CC, and between age groups in CA (P < .01). Totally 50 single-nucleotide polymorphisms (SNPs) in 10 genes have been reported with overlapping associations with RA, CA, and/or CC, with BMP3, FMNL2, HERC2, PROX1-AS1, and ZC3H11B associated with RA and CA, FBN1, NHSL1, and PDGFRA with CA and CC, TRAF3IP1 with RA and CC, and CASC15 with RA, CA, and CC.

CONCLUSIONS

This study confirms moderate heritabilities of RA, CA and CC. Through evaluating overlapping SNPs or genes between these three phenotypes, we prioritized 50 SNPs in 10 genes as candidate variants for further validation. These findings highlight the complex genetic architecture of astigmatism and indicate shared and distinct genetic markers for different astigmatism-related corneal parameters. Future studies in different populations and functional studies evaluating the roles of the involved genes in astigmatism are warranted.

Myopia in Children: Epidemiology, Genetics, and Emerging Therapies for Treatment and Prevention

Refractive errors, particularly myopia, are among the most prevalent visual impairments globally, with rising incidence in children and adolescents. This review explores the epidemiology and risk factors associated with the development of refractive errors, focusing on the environmental and lifestyle factors contributing to the current surge in myopia. We provide an overview of key genetic factors and molecular pathways driving the pathogenesis of myopia and other refractive errors, emphasizing the complex interplay between genetic predisposition and environmental triggers. Understanding the underlying mechanisms is crucial for identifying new strategies for intervention. We discuss current approaches to slow myopia progression in pediatric populations, including pharmacological treatment regimens (low-dose atropine), optical interventions, and lifestyle modifications. In addition to established therapies, we highlight emerging innovations, including new pharmacological agents and advanced optical devices, and insights into potential future treatments. Cutting-edge research into gene therapy, molecular inhibitors, and neuroprotective strategies may yield novel therapeutic targets that address the root causes of refractive errors. This comprehensive review underscores the importance of early intervention and highlights promising avenues for future research, aiming to provide pediatricians with guidance to ultimately improve clinical outcomes in managing and preventing myopia progression in children and young adults.

Targeting MicroRNA in myopia: Current insights

Myopia, the most prevalent eye condition, has sparked notable interest regarding its origin and prevention. MicroRNAs (miRNAs) are short, non-coding RNA strands typically consisting of 18-24 nucleotides. They play a central role in post-transcriptional gene regulation and are closely associated with both normal and pathological processes in organisms. Recent advances in next-generation sequencing and bioinformatics have provided novel insights into miRNA expression and its regulatory role in myopia. This review discusses the distinct expression patterns, regulatory functions, and potential pathways of miRNAs involved in the onset and progression of myopia. The primary objective of this review was to provide valuable insights into molecular mechanisms underlying myopia and the contribution of miRNAs. These insights are expected to pave the way for further exploration of the molecular mechanisms, diagnosis, treatment, and clinical applications of myopia.

Identification and characterization of extrachromosomal circular DNA in patients with high myopia and cataract

To explore the presence of extrachromosomal circular DNA (eccDNA) in the anterior capsule of the lens in the eyes of patients with cataract and with high myopia. Circle-Seq was performed to identify differences in the eccDNA and gene expression between the anterior capsule of the lens of patients with simple nuclear cataract (C, n = 6 cases) and patients with nuclear cataract along with high myopia (HM, n = 6 cases). The expression of eccDNA was confirmed using routine quantitative polymerase chain reaction. The eccDNA ranked in C and HM ranged in length from 0.017 kb - 9.9 Mb with two distinctive peaks detected at 0.2 kb and 0.5 kb, while eccDNA that were differentially expressed ranged in size from 0.05 kb - 57.8 kb with two distinctive peaks observed at 0.1 kb and 0.5 kb. Only 2.5% of the eccDNA in C and 2% in HM were>25 kb in size. The gene-rich chromosomes contributed to more number of eccDNA/Mb, while several well-known high myopia candidate genes, including catenin delta 2 (CTNND2) and ubiquitin-like with PHD, exhibited significantly increased levels of eccDNA in the anterior capsule of the lens in patients with high myopia. This study highlighted the topologic analysis of the anterior capsule of eyes with high myopia, which is an emerging direction for research and clinical applications. These findings suggested that eccDNA was commonly detected in eyes with high myopia and cataracts, and the candidate genes for high myopia identified in previous studies were also observed in the eccDNA.

Bayesian linear mixed model with multiple random effects for family-based genetic studies

Motivation: Family-based study design is one of the popular designs used in genetic research, and the whole-genome sequencing data obtained from family-based studies offer many unique features for risk prediction studies. They can not only provide a more comprehensive view of many complex diseases, but also utilize information in the design to further improve the prediction accuracy. While promising, existing analytical methods often ignore the information embedded in the study design and overlook the predictive effects of rare variants, leading to a prediction model with sub-optimal performance. Results: We proposed a Bayesian linear mixed model for the prediction analysis of sequencing data obtained from family-based studies. Our method can not only capture predictive effects from both common and rare variants, but also easily accommodate various disease model assumptions. It uses information embedded in the study design to form surrogates, where the predictive effects from unmeasured/unknown genetic and environmental risk factors can be modelled. Through extensive simulation studies and the analysis of sequencing data obtained from the Michigan State University Twin Registry study, we have demonstrated that the proposed method outperforms commonly adopted techniques. Availability: R package is available at https://github.com/yhai943/FBLMM.

A multiethnic genome-wide analysis of 19,420 individuals identifies novel loci associated with axial length and shared genetic influences with refractive error and myopia

Introduction: Long axial length (AL) is a risk factor for myopia. Although family studies indicate that AL has an important genetic component with heritability estimates up to 0.94, there have been few reports of AL-associated loci. Methods: Here, we conducted a multiethnic genome-wide association study (GWAS) of AL in 19,420 adults of European, Latino, Asian, and African ancestry from the Genetic Epidemiology Research on Adult Health and Aging (GERA) cohort, with replication in a subset of the Consortium for Refractive Error and Myopia (CREAM) cohorts of European or Asian ancestry. We further examined the effect of the identified loci on the mean spherical equivalent (MSE) within the GERA cohort. We also performed genome-wide genetic correlation analyses to quantify the genetic overlap between AL and MSE or myopia risk in the GERA European ancestry sample. Results: Our multiethnic GWA analysis of AL identified a total of 16 genomic loci, of which 5 are novel. We found that all AL-associated loci were significantly associated with MSE after Bonferroni correction. We also found that AL was genetically correlated with MSE (rg = -0.83; SE, 0.04; p = 1.95 × 10-89) and myopia (rg = 0.80; SE, 0.05; p = 2.84 × 10-55). Finally, we estimated the array heritability for AL in the GERA European ancestry sample using LD score regression, and found an overall heritability estimate of 0.37 (s.e. = 0.04). Discussion: In this large and multiethnic study, we identified novel loci, associated with AL at a genome-wide significance level, increasing substantially our understanding of the etiology of AL variation. Our results also demonstrate an association between AL-associated loci and MSE and a shared genetic basis between AL and myopia risk.

Intermixing the OPN1LW and OPN1MW Genes Disrupts the Exonic Splicing Code Causing an Array of Vision Disorders

Light absorption by photopigment molecules expressed in the photoreceptors in the retina is the first step in seeing. Two types of photoreceptors in the human retina are responsible for image formation: rods, and cones. Except at very low light levels when rods are active, all vision is based on cones. Cones mediate high acuity vision and color vision. Furthermore, they are critically important in the visual feedback mechanism that regulates refractive development of the eye during childhood. The human retina contains a mosaic of three cone types, short-wavelength (S), long-wavelength (L), and middle-wavelength (M) sensitive; however, the vast majority (~94%) are L and M cones. The OPN1LW and OPN1MW genes, located on the X-chromosome at Xq28, encode the protein component of the light-sensitive photopigments expressed in the L and M cones. Diverse haplotypes of exon 3 of the OPN1LW and OPN1MW genes arose thru unequal recombination mechanisms that have intermixed the genes. A subset of the haplotypes causes exon 3- skipping during pre-messenger RNA splicing and are associated with vision disorders. Here, we review the mechanism by which splicing defects in these genes cause vision disorders.

Myopia

Myopia, also known as short-sightedness or near-sightedness, is a very common condition that typically starts in childhood. Severe forms of myopia (pathologic myopia) are associated with a risk of other associated ophthalmic problems. This disorder affects all populations and is reaching epidemic proportions in East Asia, although there are differences in prevalence between countries. Myopia is caused by both environmental and genetic risk factors. A range of myopia management and control strategies are available that can treat this condition, but it is clear that understanding the factors involved in delaying myopia onset and slowing its progression will be key to reducing the rapid rise in its global prevalence. To achieve this goal, improved data collection using wearable technology, in combination with collection and assessment of data on demographic, genetic and environmental risk factors and with artificial intelligence are needed. Improved public health strategies focusing on early detection or prevention combined with additional effective therapeutic interventions to limit myopia progression are also needed.

Estimation of heritability and familial correlation in myopia is not affected by past sun exposure

Purpose: To consider the effect of including past sun exposure in estimating heritability and familial correlation of myopia-related traits.Methods: We calculate familial correlation and heritability of anterior chamber depth (ACD), axial length (AL), corneal curvature (CC), and spherical equivalent (SphE), with or without past sun exposure as a covariate, in a large number of unrelated nuclear families from the Raine Study (parents: Gen1, offspring: Gen2) residing in Perth, Australia, a city with a high amount of daily sunlight. Past sun exposure was objectively measured using conjunctival ultraviolet autofluorescence (CUVAF) photography.Results: When sun exposure was not included in the analysis, both familial correlation (correlation±SE; ACD: 0.308 ± 0.065, AL: 0.374 ± 0.061, CC: 0.436 ± 0.063, SphE: 0.281 ± 0.070) and heritability (ACD: 0.606 ± 0.104, AL: 0.623 ± 0.098, CC: 0.793 ± 0.079, SphE: 0.591 ± 0.106) were significant for all traits (all P < .001). However, there was no significant change in both familial correlation and heritability estimates when sun exposure was included as an additional covariate.Conclusions: Past sun exposure does not affect the estimation of the additive genetic component in myopia-related traits.

Accommodation response and spherical aberration during orthokeratology

PURPOSE

To evaluate the changes in the accommodative response and in the corneal and internal spherical aberration during 3 months of wear of orthokeratology lenses from the baseline.

METHODS

Fifty children aged 8 to 17 were recruited for a prospective study and were fitted with orthokeratology lenses. Refraction without cycloplegia, high and low uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), accommodation lag, horizontal near phoria without correction, corneal topography, corneal, and total wavefront aberration were performed at baseline, 1 day, 1 week, 1 month, and 3 months. Data were analyzed by Student's t test for related samples, repeated measures ANOVA test, and Pearson correlation test.

RESULTS

The spherical equivalent (SE) before and after 3 months was - 3.33 ± 1.60 D and - 0.30 ± 0.46 D, respectively. Accommodation lag was 0.53 ± 0.38 D and 0.20 ± 0.33 D at baseline and at 3 months, respectively. A moderate correlation between lag at the baseline and its change between baseline and the 3-month visit was found (P < 0.05; R = 0.748). The spherical aberration (SA) increased for anterior corneal and total measurement, being statistically significant for all visits (P < 0.05). The internal SA decreased: - 0.105 ± 0.006 at baseline and - 0.196 ± 0.203 at 1 week (P < 0.05). No difference between baseline and the follow-up visits in posterior corneal SA was found (P > 0.05) CONCLUSION: The negative SA of the lens increases during OK treatment compensated for the increase of the anterior corneal surface positive SA, in addition to increasing the accommodative response.

Possible Causes of Discordance in Refraction in Monozygotic Twins: Nearwork, Time Outdoors and Stochastic Variation

Purpose

To evaluate the impact of differences in nearwork and time spent outdoors on difference in refraction in monozygotic (MZ) twins.

Methods

Data on MZ twins aged 7 to 18 years from the Guangzhou Twin Eye Study were used in this analysis. A standard questionnaire was administered by personal interview to estimate time spent on nearwork and time spent outdoors. Spherical equivalent (SE) was measured by autorefraction under cycloplegia. The interaction between age and nearwork or time spent outdoors was also estimated.

Results

A total of 490 MZ twin pairs (233 male and 257 female) were eligible in this analysis, the mean age was 13.14 ± 2.49. In the mixed-effects model, nearwork difference was a risk factor of discordance in myopic SE (β = -0.11 diopter (D)/h, P = 0.009), the overall association between time outdoors difference and SE discordance was not significant (β = -0.89 (D)/h, P = 0.120) although an interaction between time spent outdoors difference and age was detected (β = 0.07 (D)/h, P = 0.002). Furthermore, difference in nearwork and time outdoors explained about 1.8% and 2.5% of the variation in SE discordance, respectively.

Conclusions

Given the very marked genetic similarity of MZ twins, and the small effects of known risk factors on SE discordance, we suggest that the SE discordance across MZ twins largely results from stochastic variations at the genomic or epigenetic levels, or from uncollected environmental factors.

Estimating heritability of refractive error in Koreans: the Korea National Health and Nutrition Examination Survey

PURPOSE

To estimate the familial correlation and heritability of refractive error in general Korean population.

METHODS

From the Korea National Health and Nutrition Examination Survey, 13 258 subjects of 7920 families, who were aged ≥19 years, were included in the study. Using variance components analysis, the additive genetic effect, or heritability, and the common and unique environmental effects on refractive error were examined, adopting common environments shared by cohabiting family or by siblings.

RESULTS

The proportions of hyperopia, myopia and high myopia in Koreans were 0.8%, 45.2% and 5.7% respectively. The correlation coefficients of spherical equivalent (SE) were 0.257 for parent-offspring pairs, 0.410 for sibling pairs and 0.112 for spouse pairs (p < 0.001 for all). Common environment shared by siblings affected the variation of SE significantly (p < 0.001), but that shared by cohabitants did not (p = 0.395). Adopting common environment shared by siblings, the heritability, common environmental effect and unique environmental effect of refractive error were 42.1 ± 3.3%, 11.8 ± 3.5% and 46.1 ± 3.9% respectively. Heritabilities of hyperopia, myopia and high myopia were 45.7%, 44.3% and 68.9% respectively. Adjusted odds ratios of myopia among offspring were 3.78 given one parent has myopia and 4.43 when both parents have myopia.

CONCLUSION

Refractive error is influenced by common environment shared by siblings. The heritability of refractive error is higher for high myopia than for myopia or hyperopia.

IMI - Myopia Genetics Report

The knowledge on the genetic background of refractive error and myopia has expanded dramatically in the past few years. This white paper aims to provide a concise summary of current genetic findings and defines the direction where development is needed. We performed an extensive literature search and conducted informal discussions with key stakeholders. Specific topics reviewed included common refractive error, any and high myopia, and myopia related to syndromes. To date, almost 200 genetic loci have been identified for refractive error and myopia, and risk variants mostly carry low risk but are highly prevalent in the general population. Several genes for secondary syndromic myopia overlap with those for common myopia. Polygenic risk scores show overrepresentation of high myopia in the higher deciles of risk. Annotated genes have a wide variety of functions, and all retinal layers appear to be sites of expression. The current genetic findings offer a world of new molecules involved in myopiagenesis. As the missing heritability is still large, further genetic advances are needed. This Committee recommends expanding large-scale, in-depth genetic studies using complementary big data analytics, consideration of gene-environment effects by thorough measurement of environmental exposures, and focus on subgroups with extreme phenotypes and high familial occurrence. Functional characterization of associated variants is simultaneously needed to bridge the knowledge gap between sequence variance and consequence for eye growth.

Association analysis of exome variants and refraction, axial length, and corneal curvature in a European-American population

Refractive errors, myopia, and hyperopia are common visual disorders greatly affecting older individuals. Refraction is determined by genetic factors but only a small percentage of its variation has been explained. We performed a genetic association analysis with three ocular phenotypes: spherical equivalent (a continous measure of refraction), axial length, and corneal curvature in 1,871 European-Americans from the Beaver Dam Eye Study. Individuals were genotyped on the Illumina exome array and imputed to the Haplotype Reference Consortium reference panel. After increasing the number of analyzed variants in targeted protein-coding regions 10-fold via imputation, we confirmed associations for two previously known loci with corneal curvature (chr4q12, rs2114039; g.55092626T > C, β = -0.03 (95% confidence interval [CI]): -0.06, -0.01, P value = 0.01) and spherical equivalent (chr15q14, rs634990; g.35006073T > C, β = -0.27, 95% CI: -0.45, -0.09, P value = 3.79 × 10-3 ). Despite increased single nucleotide polymorphism (SNP) density, we did not detect any novel significant variants after correction for multiple comparisons. In summary, we confirmed two previous loci associated with corneal curvature and spherical equivalent in a European-American population highlighting the potential biological role of those regions in these traits.

Heritability of Anterior Chamber Indices in Rural Population

OBJECTIVE

To examine the heritability of the anterior chamber depth, angle, and volume as well as the corneal volume and diameter using Pentacam in households living in underserved rural areas of Iran.

MATERIALS AND METHODS

This cross-sectional population-based study was conducted in randomly selected households living in 2 rural districts in the south and north. The data of subjects above 5 years and households in which at least 2 members (father or mother and a child) had Pentacam data were analyzed. Each subject underwent a comprehensive ophthalmic examination, with emphasis on the measurement of visual acuity and refraction, biomicroscopy, and Pentacam imaging. Heritability was estimated to investigate familial aggregation of anterior chamber indices, and the effects of age, sex, and living area were controlled for as confounding factors.

RESULTS

Of the 3851 selected individuals, 3314 participated in the study. After applying the exclusion criteria, the data of 1383 subjects from 382 households were included in the analysis. The mean age of the participants was 37.23±19.35 years (range, 6 to 93 y). The highest and lowest heritability estimates were related to the anterior chamber angle (72%) and corneal diameter (28%), respectively. The heritability percentages of the anterior chamber depth, anterior chamber volume, and corneal volume were 47%, 39%, and 57%, respectively.

CONCLUSIONS

The high heritability of the anterior chamber angle points to a high correlation between this phenotype and genetic factors. Further genetic and molecular investigations are suggested to find the related genes and understand the etiology of glaucoma.

A genetic risk score and number of myopic parents independently predict myopia

PURPOSE

To investigate whether a genetic risk score (GRS) improved performance of predicting refractive error compared to knowing a child's number of myopic parents (NMP) alone.

METHODS

This was a retrospective analysis of data from the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort study. Refractive error was assessed longitudinally between age 7-15 using non-cycloplegic autorefraction. Genetic variants (n = 149) associated with refractive error from a Consortium for Refractive Error And Myopia (CREAM) genome-wide association study were used to calculate a GRS for each child. Using refractive error at ages 7 and 15 years as the outcome variable, coefficient of determination (R² ) values were calculated via linear regression models for the predictors: NMP, GRS and a combined model.

RESULTS

Number of myopic parents was weakly predictive of refractive error in children aged 7 years, R²  = 3.0% (95% CI 1.8-4.1%, p < 0.0001) and aged 15 years, R²  = 4.8% (3.1-6.5%, p < 0.0001). The GRS was also weakly predictive; age 7 years, R²  = 1.1% (0.4-1.9%, p < 0.0001) and 15 years R²  = 2.6% (1.3-3.9%, p < 0.0001). Combining the 2 variables gave larger R² values at age 7, R²  = 3.7% (2.5-5.0%, p < 0.0001) and 15, R²  = 7.0% (5.0-9.0%, p < 0.0001). The combined model improved performance at both ages (both p < 0.0001).

CONCLUSION

A GRS improved the ability to detect children at risk of myopia independently of knowing the NMP. We speculate this may be because NMP captures information concerning environmental risk factors for myopia. Nevertheless, further gains are required to make such predictive tests worthwhile in the clinical environment.

The Influence of Parental Myopia on Children's Myopia in Different Generations of Parent-Offspring Pairs in South Korea

PURPOSE

To compare the heritabilities of myopia and high myopia across three different generations in Korea.

METHODS

Parent-offspring pairs of different age groups were included: two parents and their offspring aged 10-19 ("young families"), two parents and their offspring aged 20-29 ("middle-aged families"), and two parents and their offspring aged 30-45 ("older families") were selected from the 2008-2012 Korea National Health and Nutrition Examination Survey. Variance component methods were used to obtain the heritability estimates for myopia and high myopia using parent-offspring pairs from three generations. Spherical equivalents measured in the right eyes were used.

RESULTS

From the 2008-2012 data, 2,716, 1,211, and 477 offspring from 1,807 young, 956 middle-aged, and 434 older families were eligible for the study, respectively. For myopia, the additive genetic portion of phenotypic variance was smaller in the younger families (74.7% in the older families, 48.1% in the middle-aged families, and 40.1% in the young families), and the non-shared environmental portion was greater in the younger families (12.4% in older families, 24.9% in middle-aged families, and 46.5% in young families). In contrast, for high myopia, the additive genetic portion remained roughly constant at approximately 60% in all three generations.

CONCLUSIONS

With myopia, the environmental portion of the phenotypic variance increased and the additive genetic portion decreased as South Korea became more urbanized. With high myopia, the additive genetic portion remained roughly constant at approximately 60%, despite the urbanization.

APLP2 Regulates Refractive Error and Myopia Development in Mice and Humans

Myopia is the most common vision disorder and the leading cause of visual impairment worldwide. However, gene variants identified to date explain less than 10% of the variance in refractive error, leaving the majority of heritability unexplained (“missing heritability”). Previously, we reported that expression of APLP2 was strongly associated with myopia in a primate model. Here, we found that low-frequency variants near the 5’-end of APLP2 were associated with refractive error in a prospective UK birth cohort (n = 3,819 children; top SNP rs188663068, p = 5.0 × 10⁻⁴) and a CREAM consortium panel (n = 45,756 adults; top SNP rs7127037, p = 6.6 × 10⁻³). These variants showed evidence of differential effect on childhood longitudinal refractive error trajectories depending on time spent reading (gene x time spent reading x age interaction, p = 4.0 × 10⁻³). Furthermore, Aplp2 knockout mice developed high degrees of hyperopia (+11.5 ± 2.2 D, p < 1.0 × 10⁻⁴) compared to both heterozygous (-0.8 ± 2.0 D, p < 1.0 × 10⁻⁴) and wild-type (+0.3 ± 2.2 D, p < 1.0 × 10⁻⁴) littermates and exhibited a dose-dependent reduction in susceptibility to environmentally induced myopia (F(2, 33) = 191.0, p < 1.0 × 10⁻⁴). This phenotype was associated with reduced contrast sensitivity (F(12, 120) = 3.6, p = 1.5 × 10⁻⁴) and changes in the electrophysiological properties of retinal amacrine cells, which expressed Aplp2. This work identifies APLP2 as one of the “missing” myopia genes, demonstrating the importance of a low-frequency gene variant in the development of human myopia. It also demonstrates an important role for APLP2 in refractive development in mice and humans, suggesting a high level of evolutionary conservation of the signaling pathways underlying refractive eye development.

Gene variants identified by GWAS studies to date explain only a small fraction of myopia cases because myopia represents a complex disorder thought to be controlled by dozens or even hundreds of genes. The majority of genetic variants underlying myopia seems to be of small effect and/or low frequency, which makes them difficult to identify using classical genetic approaches, such as GWAS, alone. Here, we combined gene expression profiling in a monkey model of myopia, human GWAS, and a gene-targeted mouse model of myopia to identify one of the “missing” myopia genes, APLP2. We found that a low-frequency risk allele of APLP2 confers susceptibility to myopia only in children exposed to large amounts of daily reading, thus, providing an experimental example of the long-hypothesized gene-environment interaction between nearwork and genes underlying myopia. Functional analysis of APLP2 using an APLP2 knockout mouse model confirmed functional significance of APLP2 in refractive development and implicated a potential role of synaptic transmission at the level of glycinergic amacrine cells of the retina for the development of myopia. Furthermore, mouse studies revealed that lack of Aplp2 has a dose-dependent suppressive effect on susceptibility to form-deprivation myopia, providing a potential gene-specific target for therapeutic intervention to treat myopia.

The contributions of near work and outdoor activity to the correlation between siblings in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study

PURPOSE

We determined the correlation between sibling refractive errors adjusted for shared and unique environmental factors using data from the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study.

METHODS

Refractive error from subjects' last study visits was used to estimate the intraclass correlation coefficient (ICC) between siblings. The correlation models used environmental factors (diopter-hours and outdoor/sports activity) assessed annually from parents by survey to adjust for shared and unique environmental exposures when estimating the heritability of refractive error (2*ICC).

RESULTS

Data from 700 families contributed to the between-sibling correlation for spherical equivalent refractive error. The mean age of the children at the last visit was 13.3 ± 0.90 years. Siblings engaged in similar amounts of near and outdoor activities (correlations ranged from 0.40-0.76). The ICC for spherical equivalent, controlling for age, sex, ethnicity, and site was 0.367 (95% confidence interval [CI] = 0.304, 0.420), with an estimated heritability of no more than 0.733. After controlling for these variables, and near and outdoor/sports activities, the resulting ICC was 0.364 (95% CI = 0.304, 0.420; estimated heritability no more than 0.728, 95% CI = 0.608, 0.850). The ICCs did not differ significantly between male-female and single sex pairs.

CONCLUSIONS

Adjusting for shared family and unique, child-specific environmental factors only reduced the estimate of refractive error correlation between siblings by 0.5%. Consistent with a lack of association between myopia progression and either near work or outdoor/sports activity, substantial common environmental exposures had little effect on this correlation. Genetic effects appear to have the major role in determining the similarity of refractive error between siblings.

C-reactive protein and complement components in patients with pathological myopia

PURPOSE

To investigate the association between pathological myopia (PM) and immunological/inflammatory markers and to identify the possible risk factors for the formation of myopic choroidal neovascularization (mCNV).

METHODS

One hundred fourteen unrelated subjects were recruited: 63 PM patients (PM group) with spherical equivalent of at least -8.00 diopters (range, -8.00 to -25.00) and axial length exceeding 26.5 mm, accompanied by characteristic pathologic changes, and 51 emmetropic age- and sex-matched individuals (control group) with spherical equivalent within ±1.0 diopter in both eyes. In the PM group, patients were assigned to two subgroups, mCNV group and no CNV group, according to the results of fluorescein angiography. Serum high-sensitivity C-reactive protein (hs-CRP) and complement profile (C3, C4, and CH50) were assayed. Statistical analysis was performed between the two groups. Binary logistic regression analysis was used to analyze the relative risk factors that were associated with the development of mCNV in the PM group patients.

RESULTS

The range of axial length was 26.50 to 37.08 mm in the PM group and 22.32 to 24.56 mm in the control group. There were 24 patients in the mCNV group and 39 patients in the no CNV group. The PM group patients had significantly higher serum hs-CRP (p = 0.033), C3 (p = 0.004), and CH50 (p < 0.001) compared with the control group patients. There were no significant differences between the two groups for C4 level (p = 0.071). Binary logistic regression analysis, which included hs-CRP, C3, C4, CH50, age, and sex as covariates, showed that C3 (p = 0.03) and age (p = 0.01) were risk factors for mCNV, whereas serum hs-CRP, C4, CH50, and sex were not statistically significant predictors of mCNV in the PM group patients (p > 0.05).

CONCLUSIONS

Our data support the hypothesis that immunological/inflammatory markers, namely hs-CRP, C3, and CH50 may play an important role in the development of PM, and that C3 level may be a predictive risk factor for mCNV formation.

Nine loci for ocular axial length identified through genome-wide association studies, including shared loci with refractive error

Refractive errors are common eye disorders of public health importance worldwide. Ocular axial length (AL) is the major determinant of refraction and thus of myopia and hyperopia. We conducted a meta-analysis of genome-wide association studies for AL, combining 12,531 Europeans and 8,216 Asians. We identified eight genome-wide significant loci for AL (RSPO1, C3orf26, LAMA2, GJD2, ZNRF3, CD55, MIP, and ALPPL2) and confirmed one previously reported AL locus (ZC3H11B). Of the nine loci, five (LAMA2, GJD2, CD55, ALPPL2, and ZC3H11B) were associated with refraction in 18 independent cohorts (n = 23,591). Differential gene expression was observed for these loci in minus-lens-induced myopia mouse experiments and human ocular tissues. Two of the AL genes, RSPO1 and ZNRF3, are involved in Wnt signaling, a pathway playing a major role in the regulation of eyeball size. This study provides evidence of shared genes between AL and refraction, but importantly also suggests that these traits may have unique pathways.

Juvenile myopia progression, risk factors and interventions

The development and progression of early onset myopia is actively being investigated. While myopia is often considered a benign condition it should be considered a public health problem for its visual, quality of life, and economic consequences. Nearly half of the visually impaired population in the world has uncorrected refractive errors, with myopia a high percent of that group. Uncorrected visual acuity should be screened for and treated in order to improve academic performance, career opportunities and socio-economic status. Genetic and environmental factors contribute to the onset and progression of myopia. Twin studies have supported genetic factors and research continues to identify myopia genetic loci. While multiple myopia genetic loci have been identified establishing myopia as a common complex disorder, there is not yet a genetic model explaining myopia progression in populations. Environmental factors include near work, education levels, urban compared to rural location, and time spent outdoors. In this field of study where there continues to be etiology controversies, there is recent agreement that children who spend more time outdoors are less likely to become myopic. Worldwide population studies, some completed and some in progress, with a common protocol are gathering both genetic and environmental cohort data of great value. There have been rapid population changes in prevalence rates supporting an environmental influence. Interventions to prevent juvenile myopia progression include pharmacologic agents, glasses and contact lenses. Pharmacological interventions over 1-2 year trials have shown benefits. Peripheral vision defocus has been found to affect the emmetropization process and may be affected by wearing glasses or contacts. Accommodation accuracy also has been implicated in myopia progression. Further research will aim to assess both the role and interaction of environmental influences and genetic factors.

Time outdoors and physical activity as predictors of incident myopia in childhood: a prospective cohort study

PURPOSE

Time spent in "sports/outdoor activity" has shown a negative association with incident myopia during childhood. We investigated the association of incident myopia with time spent outdoors and physical activity separately.

METHODS

Participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) were assessed by noncycloplegic autorefraction at ages 7, 10, 11, 12, and 15 years, and classified as myopic (≤-1 diopters) or as emmetropic/hyperopic (≥-0.25 diopters) at each visit (N = 4,837-7,747). Physical activity at age 11 years was measured objectively using an accelerometer, worn for 1 week. Time spent outdoors was assessed via a parental questionnaire administered when children were aged 8-9 years. Variables associated with incident myopia were examined using Cox regression.

RESULTS

In analyses using all available data, both time spent outdoors and physical activity were associated with incident myopia, with time outdoors having the larger effect. The results were similar for analyses restricted to children classified as either nonmyopic or emmetropic/hyperopic at age 11 years. Thus, for children nonmyopic at age 11, the hazard ratio (95% confidence interval, CI) for incident myopia was 0.66 (0.47-0.93) for a high versus low amount of time spent outdoors, and 0.87 (0.76-0.99) per unit standard deviation above average increase in moderate/vigorous physical activity.

CONCLUSION

Time spent outdoors was predictive of incident myopia independently of physical activity level. The greater association observed for time outdoors suggests that the previously reported link between "sports/outdoor activity" and incident myopia is due mainly to its capture of information relating to time outdoors rather than physical activity.

Linkage analysis of quantitative refraction and refractive errors in the Beaver Dam Eye Study

PURPOSE

Refraction, as measured by spherical equivalent, is the need for an external lens to focus images on the retina. While genetic factors play an important role in the development of refractive errors, few susceptibility genes have been identified. However, several regions of linkage have been reported for myopia (2q, 4q, 7q, 12q, 17q, 18p, 22q, and Xq) and for quantitative refraction (1p, 3q, 4q, 7p, 8p, and 11p). To replicate previously identified linkage peaks and to identify novel loci that influence quantitative refraction and refractive errors, linkage analysis of spherical equivalent, myopia, and hyperopia in the Beaver Dam Eye Study was performed.

METHODS

Nonparametric, sibling-pair, genome-wide linkage analyses of refraction (spherical equivalent adjusted for age, education, and nuclear sclerosis), myopia and hyperopia in 834 sibling pairs within 486 extended pedigrees were performed.

RESULTS

Suggestive evidence of linkage was found for hyperopia on chromosome 3, region q26 (empiric P = 5.34 × 10(-4)), a region that had shown significant genome-wide evidence of linkage to refraction and some evidence of linkage to hyperopia. In addition, the analysis replicated previously reported genome-wide significant linkages to 22q11 of adjusted refraction and myopia (empiric P = 4.43 × 10(-3) and 1.48 × 10(-3), respectively) and to 7p15 of refraction (empiric P = 9.43 × 10(-4)). Evidence was also found of linkage to refraction on 7q36 (empiric P = 2.32 × 10(-3)), a region previously linked to high myopia.

CONCLUSIONS

The findings provide further evidence that genes controlling refractive errors are located on 3q26, 7p15, 7p36, and 22q11.

Heritability of ocular component dimensions in mice phenotyped using depth-enhanced swept source optical coherence tomography

The range of genetic and genomic resources available makes the mouse a powerful model for the genetic dissection of complex traits. Because accurate, high-throughput phenotypic characterisation is crucial to the success of such endeavours, we recently developed an optical coherence tomography (OCT) system with extended depth range scanning capability for measuring ocular component dimensions in mice. In order to test whether the accuracy and reproducibility of our OCT system was sufficient for gene mapping studies, we carried out an experiment designed to estimate the heritability of mouse ocular component dimensions. High-resolution, two dimensional tomograms were obtained for both eyes of 11 pairs of 8 week-old outbred MF1 mice. Subsequently, images were obtained when their offspring were aged 8 weeks. Biometric data were extracted after image segmentation, reconstruction of the geometric shape of each surface, and calculation of intraocular distances. The repeatability of measurements was evaluated for 12 mice scanned on consecutive days. Heritability estimates were calculated using variance components analysis. Sets of tomograms took ∼2 s to acquire. Biometric data could be obtained for 98% of the 130 eyes scanned. The 95% limits of repeatability ranged from ±6 to ±16 μm for the axial ocular component dimensions. The heritability of the axial ocular components was 0.6-0.8, except for corneal thickness, which had a heritability not significantly different from zero. In conclusion, axial ocular component dimensions are highly heritable in mice, as they are in humans. OCT with extended depth range scanning can be used to rapidly phenotype individual mice with sufficient accuracy and precision to permit gene mapping studies.

The heritability of ocular traits

Heritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. Many ophthalmic disorders and biometric traits are known to have a genetic basis and consequently much work has been published in the literature estimating the heritability of various ocular parameters. We collated and summarized the findings of heritability studies conducted in the field of ophthalmology. We grouped the various studies broadly by phenotype as follows: refraction, primary open-angle glaucoma, age-related macular degeneration (AMD), cataract, diabetic retinopathy, and others. A total of 82 articles were retrieved from the literature relating to estimation of heritability for an ocular disease or biometric trait; of these, 37 papers were concerned with glaucoma, 28 with refraction, 4 with AMD, 5 with diabetic retinopathy, and 4 with cataract. The highest reported heritability for an ophthalmic trait is 0.99 for the phenotype ≥ 20 small hard drusen, indicating that observed variation in this parameter is largely governed by genetic factors. Over 60% of the studies employed a twin study design and a similar percentage utilized variance components methods and structural equation modeling (SEM) to derive their heritability values. Using modern SEM techniques, heritability estimates derived from twin subjects were generally higher than those from family data. Many of the estimates are in the moderate to high range, but to date the majority of genetic variants accounting for these findings have not been uncovered, hence much work remains to be undertaken to elucidate fully their molecular etiology.

Role of the hepatocyte growth factor gene in refractive error

OBJECTIVE

Refractive errors such as myopia and hypermetropia are among the leading causes of visual impairment worldwide. Several genetic loci have been associated with myopia but none to date have been reported for hypermetropia. We investigated the hepatocyte growth factor (HGF) as a candidate gene influencing these 2 refractive error states.

DESIGN

Case-control study.

PARTICIPANTS

A total of 551 individuals (193 males, 358 females; mean age, 55.41+/-12.65 years) including 117 individuals with high myopia <or= -6.00 diopters (D), 140 individuals with low/moderate myopia (-2.00 to -5.99 D), 148 emmetropic individuals (-0.50 to +0.75 D) and 146 hyperopic individuals (>+2.00 D) were included in the analysis from 3 different Australian population cohorts (The Genes in Myopia Study, the Blue Mountains Eye Study, and the Melbourne Visual impairment project).

METHODS

Genotyping of 9 tag single nucleotide polymorphisms (SNPs) that encompassed the entire HGF gene and its associated sequences as well as 6 additional SNPs identified through DNA resequencing was undertaken.

MAIN OUTCOME MEASURES

Genetic association with refraction.

RESULTS

After correction for multiple testing, the SNPs rs12536657 (odds ratio [OR], 5.53; 95% confidence interval [CI], 1.14-26.76) and rs5745718 (OR, 2.24; 95% CI, 1.30-3.85) showed significant association with hypermetropia. Whereas the SNPs rs1743 (OR, 2.02; 95% CI, 1.19-3.43; P = .009), rs4732402 (OR, 2.03; 95% CI, 1.23-3.36; P = 0.005), rs12536657 (OR, 2.38; 95% CI, 1.40-4.05; P = 0.001), rs10272030 (OR, 2.22; 95% CI, 1.31-3.75; P = 0.003), and rs9642131 (OR, 2.44; 95% CI, 1.43-4.14; P = 0.001) showed significant association with low/moderate myopia.

CONCLUSIONS

These findings present the HGF gene as the first gene significantly associated with hypermetropia as well as providing evidence of significant association with myopia in a second ethnic population. In addition, it provides insights into the important biological mechanisms that regulate human ocular development (emmetropization), which are currently poorly understood.

Axial length: an underestimated endophenotype of myopia

Myopia is a major threat for vision health across the world. Around 1 in 4 in the West and over 3 in 4 in the East are suffering from this common eye disorder. It is a complex trait affected by both genetic and environmental determinants. Axial length is an essential man-made parameter generated from ocular biometric components. It represents a combination of anterior chamber depth, lens thickness and vitreous chamber depth. Meanwhile, it is an endophenotype of the phenotype of myopia. In the mainstream genetic studies on vision science, it is always treated only as a parameter rather than an endophenotype. However, in this article, the potential advantages are discussed for axial length analysed as an endophenotype independently. It may provide solutions for the exploration of myopia genetics.

Heritability analysis of spherical equivalent, axial length, corneal curvature, and anterior chamber depth in the Beaver Dam Eye Study

OBJECTIVE

To examine genetic influences for quantitative refraction. Spherical equivalent and its related binary traits of myopia and hyperopia are highly correlated within families. Many linkage regions have been reported for myopia, high myopia, and quantitative refraction. However, the measured phenotype of spherical equivalent is in large part dictated by the relationship between the underlying optical components of axial length, corneal curvature, and anterior chamber depth.

METHODS

Using data from the fourth visit of the Beaver Dam Eye Study, we conducted familial correlation and heritability analysis of quantitative spherical equivalent, axial length, anterior chamber depth, and corneal curvature using data from 715 individuals in 189 pedigrees.

RESULTS

Overall, every trait was highly heritable. Heritability estimates were 0.58 (SE 0.13) for spherical equivalent after adjustment for age, education, and nuclear sclerosis; 0.95 (SE 0.11) for corneal curvature after adjustment for height; 0.67 (SE 0.14) for axial length after adjustment for height and education; and 0.78 (SE 0.14) for anterior chamber depth after adjustment for age, education, height, and nuclear sclerosis.

CONCLUSION

Refraction and the underlying traits of axial length, corneal curvature, and anterior chamber depth are highly heritable. Genetic analysis of these traits may provide greater insight into the development of refractive errors.

Density of common complex ocular traits in the aging eye: analysis of secondary traits in genome-wide association studies

Genetic association studies are identifying genetic risks for common complex ocular traits such as age-related macular degeneration (AMD). The subjects used for discovery of these loci have been largely from clinic-based, case-control studies. Typically, only the primary phenotype (e.g., AMD) being studied is systematically documented and other complex traits (e.g., affecting the eye) are largely ignored. The purpose of this study was to characterize these other or secondary complex ocular traits present in the cases and controls of clinic-based studies being used for genetic study of AMD. The records of 100 consecutive new patients (of any diagnosis) age 60 or older for which all traits affecting the eye had been recorded systematically were reviewed. The average patient had 3.5 distinct diagnoses. A subset of 10 complex traits was selected for further study because they were common and could be reliably diagnosed. The density of these 10 complex ocular traits increased by 0.017 log-traits/year (P = 0.03), ranging from a predicted 2.74 at age 60 to 4.45 at age 90. Trait-trait association was observed only between AMD and primary vitreomacular traction (P = 0.0009). Only 1% of subjects age 60 or older had no common complex traits affecting the eye. Extrapolations suggested that a study of 2000 similar subjects would have sufficient power to detect genetic association with an odds ratio of 2.0 or less for 4 of these 10 traits. In conclusion, the high prevalence of complex traits affecting the aging eye and the inherent biases in referral patterns leads to the potential for confounding by undocumented secondary traits within case-control studies. In addition to the primary trait, other common ocular phenotypes should be systematically documented in genetic association studies so that adjustments for potential trait-trait associations and other bias can be made and genetic risk variants identified in secondary analyses.

A review of current approaches to identifying human genes involved in myopia

The prevalence of myopia is high in many parts of the world, particularly among the Orientals such as Chinese and Japanese. Like other complex diseases such as diabetes and hypertension, myopia is likely to be caused by both genetic and environmental factors, and possibly their interactions. Owing to multiple genes with small effects, genetic heterogeneity and phenotypic complexity, the study of the genetics of myopia poses a complex challenge. This paper reviews the current approaches to the genetic analysis of complex diseases and how these can be applied to the identification of genes that predispose humans to myopia. These approaches include parametric linkage analysis, non-parametric linkage analysis like allele-sharing methods and genetic association studies. Basic concepts, advantages and disadvantages of these approaches are discussed and explained using examples from the literature on myopia. Microsatellites and single nucleotide polymorphisms are common genetic markers in the human genome and are indispensable tools for gene mapping. High throughput genotyping of millions of such markers has become feasible and efficient with recent technological advances. In turn, this makes the identification of myopia susceptibility genes a reality.