Common variant in myocilin gene is associated with high myopia in isolated population of Korcula Island, Croatia

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.

Insight into the molecular genetics of myopia

Myopia is the most common cause of visual impairment worldwide. Genetic and environmental factors contribute to the development of myopia. Studies on the molecular genetics of myopia are well established and have implicated the important role of genetic factors. With linkage analysis, association studies, sequencing analysis, and experimental myopia studies, many of the loci and genes associated with myopia have been identified. Thus far, there has been no systemic review of the loci and genes related to non-syndromic and syndromic myopia based on the different approaches. Such a systemic review of the molecular genetics of myopia will provide clues to identify additional plausible genes for myopia and help us to understand the molecular mechanisms underlying myopia. This paper reviews recent genetic studies on myopia, summarizes all possible reported genes and loci related to myopia, and suggests implications for future studies on the molecular genetics of myopia.

Genetic association of COL1A1 polymorphisms with high myopia in Asian population: a Meta-analysis

AIM

To comprehensively evaluate the potential association of COL1A1 polymorphisms with high myopia by a systematic review and Meta-analysis.

METHODS

All association studies on COL1A1 and high myopia reported up to June 10, 2014 in PubMed, Embase, Web of Science, and the Chinese Biomedical Database were retrieved. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were analyzed for single-nucleotide polymorphisms (SNPs) using fixed- and random- effects models according to between-study heterogeneity. Publication bias analyses were conducted by Egger's test.

RESULTS

A total of four studies from reported papers were included in this analysis. The Meta-analyses for COL1A1 rs2075555, composed of 2304 high myopia patients and 2272 controls, failed to detect any significant association with high myopia. A total of 971 cases and 649 controls were tested for COL1A1 rs2269336. The association of COL1A1 rs2269336 with high myopia was observed in recessive model (CC vs CG+GG, P=0.03) and in heterozygous model (CG vs GG, P=0.04), but not in other models.

CONCLUSION

This Meta-analysis shows that COL1A1 rs2269336 (CC vs CG+GG) affects individual susceptibility to high myopia, whereas there is no association detected between SNPs rs2075555 and high myopia. Given the limited sample size, further investigations including more ethnic groups are required to validate the association.

Association of COL1A1 polymorphism with high myopia: a Meta-analysis

AIM

To investigate the association between collagen type I alpha 1 (COL1A1) gene and high myopia.

METHODS

In this Meta-analysis, we examined 5 published case-control studies that involved 1942 high myopia cases and 2929 healthy controls to assess the association between the COL1A1 rs2075555 polymorphism and high myopia risk. We calculated the pooled odds ratios (ORs) of COL1A1 rs2075555 polymorphism in high myopia cases vs healthy controls to evaluate the strength of the association.

RESULTS

Overall, there was no significant difference both in the genotype and allele distributions of COL1A1 rs2075555 polymorphism between high myopia cases and healthy controls: CC vs AA OR=1.10, 95% confidence interval (CI)=0.76-1.58; AC vs AA OR=0.98, 95%CI 0.80-1.20; CC/AC vs AA/OR=1.01, 95%CI 0.84-1.22; CC vs AC/AA OR=1.06, 95%CI=0.93-1.20; C vs A OR=1.06, 95%CI 0.91-1.23). In addition, in the stratified analyses by ethnicity, no significant associations were found in any genetic model both in European and Asia cohorts.

CONCLUSION

Our results indicate that the COL1A1 rs2075555 polymorphism may not affect susceptibility to high myopia.

Association between COL1A1 polymorphisms and high myopia: a meta-analysis

BACKGROUND

Previous studies of the association between COL1A1 polymorphisms and high myopia risk have yielded conflicting results. To help resolve the discrepancies, we performed a meta-analysis to estimate the relationship between COL1A1 polymorphisms and high myopia risk.

METHODS

We searched for case-control and cohort studies in MEDLINE, EMBASE, and OVID. Odds ratios (OR) with 95% confidence intervals (CI) were derived for single-nucleotide polymorphisms (SNPs). We also analyzed heterogeneity and publication bias.

RESULTS

This meta-analysis was based on five studies of rs2075555 (1,944 high myopia cases and 3,060 controls), and three studies of rs2269336 (1,454 high myopia cases and 1,512 controls). The combined results showed an association between rs2075555 and high myopia in the dominant (OR = 0.86, 95% CI = 0.71-0.99) and homozygote models (OR = 0.79, 95% CI = 0.64-0.97). In the recessive model for rs2269336, OR was 1.26 (95% CI = 1.05-1.50); in the heterozygote model, OR was 0.81 (95% CI = 0.69-0.96). Begg's and Egger's tests for rs2075555 showed no evidence of publication bias.

CONCLUSIONS

This meta-analysis suggests COL1A1 rs2075555 is a potential low risk factor for high myopia.

Evaluation of MYOC, ACAN, HGF, and MET as candidate genes for high myopia in a Han Chinese population

AIM

To investigate the association between high myopia (HM) and single nucleotide polymorphisms (SNPs) in the myocilin (MYOC), hepatocyte growth factor (HGF), hepatocyte growth factor receptor (MET), and aggrecan (ACAN) genes in a Han Chinese population.

METHODS

Sixteen SNPs were genotyped by the SNaPshot method in a subject group composed of 1052 HM patients and 1070 controls. Statistical analysis was performed to determine the association between the SNPs and the susceptibility of HM.

RESULTS

Two SNPs (rs3784757 and rs1516794) in ACAN were significantly associated with HM (p=0.0334 and 0.0236, odds ratio [OR]=0.83 and 0.79, respectively). The risk haplotype CA and the protective haplotype TT, generated by rs3784757 and rs1516794, showed significant association with HM (p=0.0327 and 0.0304, OR=1.21 and 0.80, respectively). Two SNPs (rs38857 and rs10215153) in MET and one SNP (rs3784757) in ACAN showed significant association with HM (p=0.0064, 0.0113, and 0.0373; OR=4.14, 5.74 and 0.52; respectively) in the recessive model. None of the other SNPs showed significant association with HM.

CONCLUSIONS

Our results suggested that genetic variants in ACAN and MET are associated with HM. Functional roles of ACAN and MET in the development of HM need to be further investigated.

Whole genome expression profiling of normal human fetal and adult ocular tissues

To study growth and development of ocular tissues, gene expression patterns in normal human fetal versus adult eyes were compared. Human retina/retinal pigment epithelium, choroid, sclera, optic nerve* and cornea* tissues were dissected from fetal (24 week gestational age) (N = 9; *N = 6), and adult (N = 6) normal donor eyes. The Illumina(®) whole genome expression microarray platform was used to assess differential expression. Statistical significance for all comparisons was determined using the Benjamin and Hochberg False Discovery Rate (FDR, 5%). Significant gene expression fold changes > 1.5 were found in adult versus fetal retina/RPE (N = 1185), choroid (N = 6446), sclera (N = 1349), and cornea (N = 3872), but not optic nerve. Genes showing differential expression were assessed using Ingenuity Pathway Analysis (IPA) for enriched functions and canonical pathways. In all tissues, development, cell death/growth, cancer functions, and signaling canonical pathways were enriched. There was also a general trend of down-regulation of collagen genes in adult tissues.

Myopia and diabetes mellitus as modificatory factors of glaucomatous optic neuropathy

Myopic deformation of the eye and metabolic alterations of the nerve tissue of patients with diabetes may modify glaucomatous optic neuropathy (GON). Blockage of axonal transport of neurotrophic factors (NTFs) is the event crucial to understanding the factors that affect GON. The primary, but not sole, blockage site is at the lamina cribrosa (LC). Other than this primary site of damage at the LC, 7 other factors may explain atypical nerve fiber layer (NFL) defects and the vulnerability of the nerve fibers in eyes with high myopia and glaucoma: a second point of blockage at the edge of the posterior scleral foramen; ectatic strain on the NFL; ectasia and distortion of the LC; association of a hypoplastic optic disc; thin and weak collagen fibers; peripapillary chorioretinal atrophy; and myopic neuropathy. Among diabetic patients, diabetic neuropathy in the retinal NFL is present initially, and increased resistance to aqueous outflow leads to ocular hypertension. Superimposition of GON on diabetic neuropathy and ocular hypertension in patients with diabetes may enhance their susceptibility to nerve damage. Results of a meta-analysis study suggested a positive association between diabetes mellitus and glaucoma whereas other reports suggested that leakage of vascular endothelial growth factor, a survival mechanism of ischemic neural tissue, and enhanced stiffness of the LC as a result of diabetic glycation may protect neurons from apoptosis. Thus, modification of GON as a result of diabetes remains controversial.

Genetic contributions to myopic refractive error: Insights from human studies and supporting evidence from animal models

Genetic studies of both population-based and recruited affected patient cohorts have identified a number of genomic regions and candidate genes that may contribute to myopic development. Scientists have developed animal models of myopia, as collection of affected tissues from patents is impractical. Recent advances in whole exome sequencing technology show promise for further elucidation of disease causing variants as in the recent identification of rare variants within ZNF644 segregating with pathological myopia. We present a review of the current research trends and findings on genetic contributions to myopic refraction including candidate loci for myopic development and their genomic convergence with expression studies of animal models inducing myopic development.

Experimental murine myopia induces collagen type Iα1 (COL1A1) DNA methylation and altered COL1A1 messenger RNA expression in sclera

PURPOSE

To investigate whether myopia development is associated with changes of scleral DNA methylation in cytosine-phosphate-guanine (CpG) sites in the collagen 1A1 (COL1A1) promoter and messenger RNA (mRNA) levels following murine form deprivation myopia.

METHODS

Fifty-seven C57BL/6 mice (postnatal day 23) were randomly assigned to four groups: (1) monocular form deprivation (MD) in which a diffuser lens was placed over one eye for 28 days; (2) normal controls without MD; (3) MD recovery in which the diffuser lens was removed for seven days; and (4) MD recovery normal controls. The DNA methylation pattern in COL1A1 promoter and exon 1 was determined by bisulfite DNA sequencing, and the COL1A1 mRNA level in sclera was determined by quantitative PCR.

RESULTS

MD was found to induce myopia in the treated eyes. Six CpG sites in the promoter and exon 1 region of COL1A1 were methylated with significantly higher frequency in the treated eyes than normal control eyes (p<0.05), with CpG island methylation in MD-contralateral eyes being intermediate. Consistent with the CpG methylation, scleral COL1A1 mRNA was reduced by 57% in the MD-treated eyes compared to normal controls (p<0.05). After seven days of MD recovery, CpG methylation was significantly reduced (p=0.01). The methylation patterns returned to near normal level in five CpG sites, but the sixth was hypomethylated compared to normal controls.

CONCLUSIONS

In parallel with the development of myopia and the reduced COL1A1 mRNA, the frequency of methylation in CpG sites of the COL1A1 promoter/exon 1 increased during MD and returned to near normal during recovery. Thus, hypermethylation of CpG sites in the promoter/exon 1 of COL1A1 may underlie reduced collagen synthesis at the transcriptional level in myopic scleras.

Nature and nurture: the complex genetics of myopia and refractive error

The refractive errors, myopia and hyperopia, are optical defects of the visual system that can cause blurred vision. Uncorrected refractive errors are the most common causes of visual impairment worldwide. It is estimated that 2.5 billion people will be affected by myopia alone within the next decade. Experimental, epidemiological and clinical research has shown that refractive development is influenced by both environmental and genetic factors. Animal models have showed that eye growth and refractive maturation during infancy are tightly regulated by visually guided mechanisms. Observational data in human populations provide compelling evidence that environmental influences and individual behavioral factors play crucial roles in myopia susceptibility. Nevertheless, the majority of the variance of refractive error within populations is thought to be because of hereditary factors. Genetic linkage studies have mapped two dozen loci, while association studies have implicated more than 25 different genes in refractive variation. Many of these genes are involved in common biological pathways known to mediate extracellular matrix (ECM) composition and regulate connective tissue remodeling. Other associated genomic regions suggest novel mechanisms in the etiology of human myopia, such as mitochondrial-mediated cell death or photoreceptor-mediated visual signal transmission. Taken together, observational and experimental studies have revealed the complex nature of human refractive variation, which likely involves variants in several genes and functional pathways. Multiway interactions between genes and/or environmental factors may also be important in determining individual risks of myopia, and may help explain the complex pattern of refractive error in human populations.

Risk factor analysis of 167 patients with high myopia

AIM

To analyze the risk factors of age, sex, course, best corrected visual acuity (BCVA), diopter and fundus features of high myopes with progressive high myopia.

METHODS

A total of 167 patients with high myopes were categorized into four groups: group 1, age 10-29 years; group 2, age 30-49 years; group 3, age 50-69 years and group 4, age 70-89 years. The refractive errors of all patients were measured without cycloplegia with an autorefractometer. Data of the spherical equivalent (SE) of the refractive errors in diopters (D) and fundus examined by direct ophthalmoscope were used in statistical analysis.

RESULTS

The number of female was statistically larger than that of male (P<0.01), also the disease course was correlated to the age. The visual acuity of high myopes significantly decreased as they grew older including the higher incidence of lacquer cracker, submacular hemorrhage, Fuchs spots, chorioretinal atrophy.

CONCLUSION

Female maybe a risk factor of high myopia, advanced age is an important factor of visual acuity decreased. High myopes ought to be treated early to delay the progress of myopia and development of macular degeneration.

Myopia genetics: a review of current research and emerging trends

PURPOSE OF REVIEW

Myopia, or nearsightedness, is the most common human eye disorder in the world and is a significant global public health concern. Along with cataract, macular degeneration, infectious disease, and vitamin A deficiency, myopia is one of the most important causes of visual impairment worldwide. Severe or high-grade myopia is a leading cause of blindness because of its associated ocular comorbidities of retinal detachment, macular choroidal degeneration, premature cataract, and glaucoma. Ample epidemiologic and molecular genetic studies support heritability of the nonsyndromic forms of this condition.

RECENT FINDINGS

Multiple myopia genetic loci have been identified, establishing this entity as a common complex disorder and underscoring the suitability for gene inquiry studies. Animal model research, primarily using form-deprivation techniques, implicates multiple altered regulation of biological substances in the ocular wall layers, which provides important information for prioritizing human candidate gene studies. Recent epidemiologic work supports a greater role for outdoor activity in relieving myopia progression rather than the previous touted young-age near-work activity model.

SUMMARY

The identification of myopia susceptibility genes will not only provide insight into the molecular basis of this significant eye disorder, but will also identify pathways involved in eye growth and development. This effort may lead to effective therapies to treat or potentially prevent this common eye condition.