Role of the hepatocyte growth factor gene in refractive error

Whole-Exome Sequencing Among School-Aged Children With High Myopia

Importance

High myopia (HM) is one of the leading causes of visual impairment worldwide. Genetic factors are known to play an important role in the development of HM.

Objective

To identify risk variants in a large HM cohort and to examine the implications of genetic testing of schoolchildren with HM.

Design, Setting, and Participants

This cohort study retrospectively reviewed whole-exome sequencing (WES) results in 6215 schoolchildren with HM who underwent genetic testing between September 2019 and July 2020 in Wenzhou City, China. HM is defined as a spherical equivalent refraction (SER) of -6.00 diopters (D) or less. The study setting was a genetic testing laboratory and a multicenter school census. Data were analyzed from July 2021 to June 2022.

Main Outcomes and Measures

The frequency and distribution of positive germline variants, the percentage of individuals with HM in both eyes, and subsequent variant yield for common high myopia (CHM; -8.00 D ≤ SER ≤ -6.00 D), ultra myopia (UM; -10.00 D ≤ SER < -8.00 D), and extreme myopia (EM; SER < -10.00 D).

Results

Of the 6215 schoolchildren with HM, 3278 (52.74%) were male. Their mean (SD) age was 14.87 (2.02) years, including 355 students in primary school, 1970 in junior high school, and 3890 in senior high school. The mean (SD) SER was -7.51 (-1.36) D for the right eye and -7.46 (-1.34) D for the left eye. Among schoolchildren with HM, genetic testing yielded 271 potential pathogenic variants in 75 HM candidate genes in 964 diagnoses (15.52%). A total of 36 known variants were found in 490 HM participants (7.88%) and 235 protein-truncating variants (PTVs) in 506 participants (8.14%). Involved variant yield was significantly positively associated with SER (Cochran-Armitage test for trend Z = 2.5492; P = .01), which ranged from 7.66% in the CHM group, 8.70% in the UM group, to 11.90% in the EM group. We also found that primary school students with EM had the highest variant yield of PTVs (8 of 35 students [22.86%]), which was 1.77 and 4.78 times that of the UM and CHM, respectively.

Conclusions and Relevance

In this cohort study of WES for HM, several potential pathogenic variants were identified in a substantial number of schoolchildren with HM. The high variation frequency in younger students with EM can provide clues for genetic screening and clinical examinations of HM to promote long-term follow-up assessment.

Identification of deleterious nsSNPs in human HGF gene: in silico approach

HGF is a protein that binds to the hepatocyte growth factor receptor to regulate cell growth, cell motility and morphogenesis in different cells and tissues. Several bioinformatics tools and in silico methods were used to identify most deleterious nsSNPs that might change the structure and function of HGF protein. The in silico tools such as SIFT, SNP&GO and PolyPhen2 were used to distinguish deleterious nsSNPs from neutral ones. Protein stability is analysed by I-Mutant, MUpro and iStable. The functional and structural effects are predicted by other tools like MutPred2, Maestro, DUET etc. Analysis of structure was performed by HOPE and Mutation3D. SWISS-MODEL. server, was used for wild type and mutant proteins 3-D Modelling. Gene-gene and protein-protein interaction were predicted by GeneMANIA and STRING, respectively. The wildtype HGF protein and these three variants were independently docked with their close interactor protein MET by the use of ClusPro. Our study suggested that out of 392 missense nsSNPs of the HGF gene, five nsSNPs (D358G, G648R, I550N, N175S and R220Q), are the most deleterious in HGF gene. Gene-gene interactions showed relation of HGF with other genes depicting its importance in several pathways and co-expressions. The protein-protein interacting network is composed of 11 nodes. Analysis of protein stability by different tools indicated that the five nsSNPS decreased the stability of the protein. Anyway these nsSNPs need a confirmation analysis by experimental investigation and GWAS studiesCommunicated by Ramaswamy H. Sarma.

Association of eleven single nucleotide polymorphisms with refractive disorders from Eskisehir, Turkey

AIM

To investigate relationship between refractive errors and eleven single nucleotide polymorphisms (SNPs) in HGF, GC, MFN1, GNB4, and VDR genes in Turkish population.

METHODS

A group of 212 participants with myopia (n=91), hyperopia (n=45), and emmetropia (n=76) were investigated in this study. SNPs in HGF, GC, MFN1, GNB4 and VDR genes were studied by SnapShot technique.

RESULTS

The patients in this study consists of 47 female/44 male (age: 23.47±4.30) patients with myopia, 20 female/25 male (age: 31.20±8.02) with hyperopia and 33 female/43 male (age: 25.22±6.60) with emmetropia. The genotype distribution of the rs7618348 polymorphism, which was the only statistically significant one between myopia and emmetropia group. The genotype distribution of the rs3819545, rs3735520, rs7041, and rs2239182 polymorphisms, which were statistically significant between hyperopia and emmetropia groups.

CONCLUSION

The importance of genetic predisposition to refractive errors with respect to etiology of the disease is revealed. It is known that polymorphism studies may differ because of genetic diversity among populations so larger cohort studies are required in different populations to enlighten the etiology of the refractive errors.

Updates on Genes and Genetic Mechanisms Implicated in Primary Angle-Closure Glaucoma

Primary angle-closure glaucoma (PACG) is estimated to affect over 30 million people worldwide by 2040 and is highly prevalent in the Asian population. PACG is more severe and carries three times the higher risk of blindness than primary open-angle glaucoma, thus representing a significant public health concern. High heritability and ethnic-specific predisposition to PACG suggest the involvement of genetic factors in disease development. In the recent past, genetic studies have led to the successful identification of several genes and loci associated with PACG across different ethnicities. The precise cellular and molecular roles of these multiple loci in the development and progression of PACG remains to be elucidated. Nonetheless, these studies have significantly increased our understanding of the emerging cellular processes and biological pathways that might provide more significant insights into the disease’s genetic etiology and may be valuable for future clinical applications. This review aims to summarize and update the current knowledge of PACG genetics analysis research.

Variants in FLRT3 and SLC35E2B identified using exome sequencing in seven high myopia families from Central Europe

PURPOSE

High myopia (HM) is an eye disorder with both environmental and genetic factors involved. Many genetic factors responsible for HM were recognized worldwide, but little is known about genetic variants underlying HM in Central Europe. Thus, the aim of this study was to identify rare sequence variants involved in HM in families from Central Europe to better understand the genetic basis of HM.

MATERIALS AND METHODS

We assessed 17 individuals from 7 unrelated Central European families with hereditary HM using exome sequencing (ES). Segregation of selected variants in other available family members was performed using Sanger sequencing.

RESULTS

Detected 73 rare variants were selected for verification. We observed 2 missense variants, c.938C>T in SLC35E2B - encoding solute carrier family 35 member E2B, and c.1642G>C in FLRT3 - encoding fibronectin leucine rich transmembrane protein, segregating with HM in one family.

CONCLUSIONS

FLRT3 ​and/or ​SLC35E2B ​could represent disease candidate genes and identified sequence variants might be responsible for HM in the studied family.

Imbalance Between Oxidative Stress and Growth Factors in Human High Myopia

Myopia is one of the commonest eye pathologies that could affect 2.56 billion people by 2020. Today high myopia is a leading cause of blindness worldwide due to associated ocular illness. Nevertheless, the cellular bases for these diseases to develop are unclear in many areas. We conducted a prospective study of oxidative stress and growth factors in human myopic and non myopic eyes in an attempt to increase our understanding of the underlying physiopathological conditions to adequately early diagnose, prevent and treat the retina problem that derives from myopia. Aqueous humor samples were obtained from 41 patients being operated for cataracts in our hospital. Axial length, refractive status and complete ophthalmologic examination were recorded. The VEGF and HGF levels were determined by an ELISA kit. Total antioxidant capacity and total nitrites/nitrate levels were established with a lab kit. We show for the first time an increase in the total nitrite levels in high myopia. We also propose for the first time the concurrence of three factors: myopia, oxidative stress, and oxidative stress together with growth factors in the same group of patients. In this way, it would not be accurate to envision high myopia as a type of normal myopia, but one with more diopters or longer axial length.

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.

HGF-rs12536657 and Ocular Biometric Parameters in Hyperopic Children, Emmetropic Adolescents, and Young Adults: A Multicenter Quantitative Trait Study

Introduction

Even though ocular refractive state is highly heritable and under strong genetic control, the identification of susceptibility genes remains a challenge. Several HGF (hepatocyte growth factor) gene variants have been associated with ocular refractive errors and corneal pathology.

Purpose

Here, we assess the association of an HGF gene variant, previously reported as associated with hyperopia, and ocular biometric parameters in a multicenter Spanish cohort.

Methods

An observational prospective multicenter cross-sectional study was designed, including a total of 403 unrelated subjects comprising 188 hyperopic children (5 to 17 years) and 2 control groups: 52 emmetropic adolescents (13 to 17 years) and 163 emmetropic young adults (18 to 28 years). Each individual underwent a comprehensive eye examination including cycloplegic refraction, and topographic and ocular biometric analysis. Genomic DNA was extracted from oral swabs. HGF single nucleotide polymorphism (SNP) rs12536657 was genotyped. Genotypic, allelic, and logistic regression analyses were performed comparing the different groups. A quantitative trait association test analyzing several biometric parameters was also performed using generalized estimating equations (GEEs) adjusting for age and gender.

Results

No association between rs12536657 and hyperopia was found through gender-adjusted logistic regression comparing the hyperopic children with either of the two control groups. Significant associations between mean topographic corneal curvature and rs12536657 for G/A (slope = +0.32; CI 95%: 0.04-0.60; p=0.023) and A/A (slope = +0.76; CI 95%: 0.12-1.40; p=0.020) genotypes were observed with the age- and gender-adjusted univariate GEE model. Both flat and steep corneal topographic meridians were also significantly associated with rs12536657 for the G/A and A/A genotypes. No association was found between rs12536657 and any other topographic or biometric measurements.

Conclusions

Our results support a possible role for HGF gene variant rs12536657 in corneal curvature in our population. To our knowledge, this is the first multicenter quantitative trait association study of HGF genotypes and ocular biometric parameters comprising a pediatric cohort.

HOXA9 is a novel myopia risk gene

Purpose

A recent meta-analysis revealed PAX6 as a risk gene for myopia. There is a link between PAX6 and HOXA9. Furthermore, HOXA9 has been reported to activate TGF-β that is a risk factor for myopia. We speculate HOXA9 may participate in myopia development.

Methods

The Singapore GUSTO birth cohort provides data on children’s cycloplegic refraction measured at age of 3 years and their methylation profile based on the umbilical cord DNA. The HOXA9 expression levels were measured in the eyes of mono-ocular form deprivation myopia in mice. The plasmid with the mouse HOXA9 cDNA was constructed and then transfected to mouse primary retinal pigment epithelial (RPE) cells. The expression levels of myopia-related genes and cell proliferation were measured in the HOXA9-overexpressed RPE cells.

Results

A total of 519 children had data on methylation profile and cycloplegic refraction. The mean spherical equivalent refraction (SE) was 0.90D. Among 8 SE outliers (worse than -2D), 7 children had HOXA9 hypomethylation. The HOXA9 levels in the retina of myopic eyes was 2.65-fold (p = 0.029; paired t-test) higher than the uncovered fellow eyes. When HOXA9 was over-expressed in the RPE cells, TGF-β, MMP2, FGF2 and IGF1R expression levels were dose-dependently increased by HOXA9. However, over-expression of HOXA9 had no significant influence on IGF1 or HGF expression. In addition, HOXA9 also increased RPE proliferation.

Conclusion

Based on the human, animal and cellular data, the transcription factor HOXA9 may promote the expression of pro-myopia genes and RPE proliferation, which eventually contribute to myopia development.

Association of Genes implicated in primary angle-closure Glaucoma and the ocular biometric parameters of anterior chamber depth and axial length in a northern Chinese population

Background

The membrane frizzled-related protein (MFRP) gene is involved in axial length (AL) regulation and MFRP mutations cause nanophthalmos; also, the hepatocyte growth factor (HGF) gene is reported to result in morphologic changes of the anterior segment and abnormal aqueous regulation that increases the risk of primary angle-closure glaucoma (PACG), while the zinc ring finger 3 (ZNRF3) gene is associated with AL. The present study investigated the association of single nucleotide polymorphisms (SNPs) in ZNRF3, HGF and MFRP with PACG in a northern Chinese population, as well as the association of these SNPs with the ocular biometric parameters of anterior chamber depth (ACD) and AL.

Methods

A total of 500 PACG patients and 720 controls were recruited. All individuals were genotyped for 12 SNPs in three genes (rs7290117, rs2179129, rs4823006 and rs3178915 in ZNRF3; rs5745718, rs12536657, rs12540393, rs17427817 and rs3735520 in HGF, rs2510143, rs36015759 and rs3814762 in MFRP) using an improved multiplex ligation detection reaction (iMLDR) technique. Genotypic distribution was analyzed for Hardy-Weinberg equilibrium. Differences in the allelic and genotypic frequencies were evaluated and adjusted by age and sex. Linkage disequilibrium (LD) patterns were tested and haplotype analysis was conducted by a logistic regression model. Generalized estimation equation (GEE) analysis was conducted using SPSS for primary association testing between genotypes and ocular biometric parameters. Bonferroni corrections for multiple comparisons were performed, and the statistical power was calculated by power and sample size calculations.

Results

The rs7290117 SNP in ZNRF3 was significantly associated with the AL, with a p-value of 0.002. We did not observe any significant associations between the SNPs and PACG or ACD. In a stratification analysis by ethnicity, rs12540393 and rs17427817 in HGF showed a nominal association with PACG in the Hui cohort, although significance was lost after correction.

Conclusions

The present study suggests rs7290117 in ZNRF3 may be involved in the regulation of AL, though our results do not support a contribution of the SNPs we tested in ZNRF3, HGF and MFRP to PACG in northern Chinese people. Further studies in a larger population are warranted to confirm this conclusion.

An analytical enrichment-based review of structural genetic studies on keratoconus

Keratoconus is a progressive bilateral corneal protrusion that leads to irregular astigmatism and impairment of vision. Keratoconus is an etiologically heterogeneous corneal dystrophy and both environmental and genetic factors play a role in its etiopathogenesis. In this analytical review, we have studied all the genes that are structurally associated with keratoconus and have tried to explain the function of each gene and its association with other eye disorders in a concise way. In addition, using gene set enrichment analysis, it was attempted to find the most important impaired metabolic pathways in keratoconus. Several genetic studies have been carried out on keratoconus and several genes have been identified as risk factors involved in the etiology of the disease. In the current study, 16 studies, including nine association studies, five genome-wide association studies, one linkage study, and one meta-analysis, were reviewed and based on the 19 genes found, enrichment was performed and the most important metabolic pathways involved in the disease were identified. The enrichment results indicated that the two pathways, interleukin 1 processing and assembly of collagen fibrils, are significantly associated with the disease. Obviously, the results of this study, in addition to providing information about the genes involved in the disease, can provide an integrated insight into the gene-based etiology of keratoconus and therapeutic opportunities thereof.

Genetics in Keratoconus - What is New?

Background:

Keratoconus is characterized as a bilateral, progressive, non-inflammatory thinning of the cornea resulting in blurred vision due to irregular astigmatism. Keratoconus has a multifactorial etiology, with multiple genetic and environmental components contributing to the disease pathophysiology. Several genomic loci and genes have been identified that highlight the complex molecular etiology of this disease.

Conclusion:

The review focuses on current knowledge of these genetic risk factors associated with keratoconus.

A review of keratoconus: Diagnosis, pathophysiology, and genetics

We discuss new approaches to the early detection of keratoconus and recent investigations regarding the nature of its pathophysiology. We review the current evidence for its complex genetics and evaluate the presently identified genes/loci and potential candidate gene/loci. In addition, we highlight current research methodologies that may be used to further elucidate the pathogenesis of keratoconus.

Genetic Associations of Primary Angle-Closure Disease: A Systematic Review and Meta-analysis

TOPIC

Systematic review and meta-analysis of the genetic associations of primary angle-closure disease (PACD).

CLINICAL RELEVANCE

To confirm the genetic biomarkers for PACD, including primary angle-closure glaucoma (PACG) and related phenotypes.

METHODS

We searched in the MEDLINE and EMBASE databases for genetic studies of PACG or other PACD published from the start dates of the databases to May 11, 2015. We estimated the summary odds ratios (ORs) and 95% confidence intervals (CIs) for each polymorphism in PACG, primary angle-closure suspect (PACS), and primary angle-closure (PAC) using fixed- or random-effect models. We also performed sensitivity analysis to test the robustness of the results.

RESULTS

Our literature search yielded 6463 reports. Among them, we identified 24 studies that fulfilled the eligibility criteria for meta-analysis, involving 28 polymorphisms in 11 genes/loci. We affirmed the association of PACG and combined PACS/PAC/PACG with 10 polymorphisms in 8 genes/loci, including COL11A1 (rs3753841-G, OR, 1.22; P = 0.00046), HGF (rs17427817-C, OR, 2.02; P = 6.9E-07; rs5745718-A, OR, 2.11; P = 9.9E-07), HSP70 (rs1043618, GG+GC, OR, 0.52; P = 0.0010), MFRP (rs2510143-C, OR, 0.66; P = 0.012; rs3814762-G, OR, 1.40; P = 0.0090), MMP9 (rs3918249-C, OR, 1.35; P = 0.034), NOS3 (rs7830-A, OR, 0.80; P = 0.036), PLEKHA7 (rs11024102-G, OR, 1.24; P = 8.3E-05), and PCMTD1-ST18 (rs1015213-A, OR, 1.59; P = 0.00013). Sensitivity analysis indicated that the results were robust.

CONCLUSIONS

In this study, we confirmed multiple polymorphisms in 8 genes/loci as genetic biomarkers for PACD, among which 3 were identified in a genome-wide association study (COL11A1, PLEKHA7, and PCMTD1-ST18), and 5 were identified in candidate gene studies (HGF, HSP70, MFRP, MMP9, and NOS3).

The genetic and environmental factors for keratoconus

Keratoconus (KC) is the most common cornea ectatic disorder. It is characterized by a cone-shaped thin cornea leading to myopia, irregular astigmatism, and vision impairment. It affects all ethnic groups and both genders. Both environmental and genetic factors may contribute to its pathogenesis. This review is to summarize the current research development in KC epidemiology and genetic etiology. Environmental factors include but are not limited to eye rubbing, atopy, sun exposure, and geography. Genetic discoveries have been reviewed with evidence from family-based linkage analysis and fine mapping in linkage region, genome-wide association studies, and candidate genes analyses. A number of genes have been discovered at a relatively rapid pace. The detailed molecular mechanism underlying KC pathogenesis will significantly advance our understanding of KC and promote the development of potential therapies.

Genetic and genomic perspective to understand the molecular pathogenesis of keratoconus

Keratoconus (KC; Mendelian Inheritance in Man (OMIM) 14830) is a bilateral, progressive corneal defect affecting all ethnic groups around the world. It is the leading cause of corneal transplantation. The age of onset is at puberty, and the disorder is progressive until the 3^rd–4^th decade of life when it usually arrests. It is one of the major ocular problems with significant social and economic impacts as the disease affects young generation. Although genetic and environmental factors are associated with KC, but the precise etiology is still elusive. Results from complex segregation analysis suggests that genetic abnormalities may play an essential role in the susceptibility to KC. Due to genetic heterogeneity, a recent study revealed 17 different genomic loci identified in KC families by linkage mapping in various populations. The focus of this review is to provide a concise update on the current knowledge of the genetic basis of KC and genomic approaches to understand the disease pathogenesis.

Association of the hepatocyte growth factor gene with keratoconus in an Australian population

PURPOSE

A previous study has indicated suggestive association of the hepatocyte growth factor (HGF) gene with Keratoconus. We wished to assess this association in an independent Caucasian cohort as well as assess its association with corneal curvature.

PARTICIPANTS

Keratoconus patients were recruited from private and public clinics in Melbourne, Australia. Non-keratoconic individuals were identified from the Genes in Myopia (GEM) study from Australia. A total of 830 individuals were used for the analysis including 157 keratoconic and 673 non keratoconic subjects.

METHODS

Tag single nucleotide polymorphisms (tSNPs) were chosen to encompass the hepatocyte growth factor gene as well as 2 kb upstream of the start codon through to 2 kb downstream of the stop codon. Logistic and linear regression including age and gender as covariates were applied in statistical analysis with subsequent Bonferroni correction.

RESULTS

Ten tSNPs were genotyped. Following statistical analysis and multiple testing correction, a statistically significant association was found for the tSNP rs2286194 {p = 1.1×10-(3) Odds Ratio 0.52, 95% CI--0.35, 0.77} for keratoconus. No association was found between the 10 tSNPs and corneal curvature.

CONCLUSIONS

These findings provide additional evidence of significant association of the HGF gene with Keratoconus. This association does not appear to act through the corneal curvature route.

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.

Hepatocyte growth factor genetic variations and primary angle-closure glaucoma in the Han Chinese population

PURPOSE

The aim of this study is to examine whether or not hepatocyte growth factor (HGF) genetic variations are associated with susceptibility to primary angle-closure glaucoma (PACG) in the Han Chinese population.

METHODS

Three single-nucleotide polymorphisms (SNPs)-rs5745718, rs17427817, and rs3735520-in the HGF gene were genotyped in 238 adult patients with PACG and 287 age-, sex-, and ethnically matched healthy controls by using a polymerase chain reaction restriction fragment length polymorphism assay. Data was analyzed by χ(2) analysis.

RESULTS

The three tested analyzed polymorphisms in the HGF gene were in Hardy-Weinberg equilibrium, in all the subjects. The frequencies of the genotype and allele of rs5745718 and rs1742817 in the HGF gene were significantly different between the PACG patients and the controls. On one hand, the frequencies of the CC genotype and C allele of rs5745718 were significantly decreased in PACG patients compared with controls (Pc = 1.40×10(-3); Pc = 3.21×10(-4), respectively); however, on the other hand, significantly decreased frequencies of the GG genotype and the G allele of rs17427817 were observed in PACG patients compared with the controls (Pc = 0.006,; Pc = 6.06×10(-4), respectively). A comparison of the distributions of the genotypes and alleles of rs3735520 showed no statistically significant differences between the PACG patients and the controls (pc>0.05). The haplotype analysis results showed that the CGC haplotype frequency was significantly decreased in the patients with PACG compared with the controls (pc<0.001). No difference was detected between the patients and the controls with regard to the other haplotypes.

CONCLUSIONS

Our study suggests that rs5745718 and rs17427817 are associated with a decreased risk of PACG in the Chinese Han population. The CGC haplotype was demonstrated to possibly play a protective role against PACG in this population.

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.

The Australian Twin Registry as a Resource For Genetic Studies into Ophthalmic Traits

The Australian Twin Registry (ATR) is a not-for-profit organization that coordinates research involving Australian twins and researchers. The ATR is one of the largest volunteer registries of its kind and contains over 33,000 twin pairs. The purpose of this review is to provide a broad overview of recent ophthalmic studies that have utilized the ATR for recruitment purposes. Such studies include the Australian Twin Eye Study (ATES) and the Genes in Myopia (GEM) study. The ATES and GEM studies have undertaken studies into the genetic influences on a number of ophthalmic traits through the use of heritability studies, linkage studies, genome-wide association studies, and candidate gene-based studies. An overview of these studies is provided in this review, as well as a description of the recruitment methodologies for both the ATES and GEM studies.

The Genetics of Keratoconus: A Review

Keratoconus is the most common ectatic disorder of the corneal. Genetic and environmental factors may contribute to its pathogenesis. The focus of this article is to summarize current research into the complex genetics of keratoconus. We discuss the evidence of genetic etiology including family-based linkage studies, twin studies, genetic mutations, and genome-wide association studies. The genes implicated potentially include VSX1, miR-184, DOCK9, SOD1, RAB3GAP1, and HGF. Besides the coding mutations, we also highlight the potential contribution of DNA copy number variants in the pathogenesis of keratoconus. Finally, we present future directions for genetic research in the understanding of the complex genetics of keratoconus and its clinical significance. As new functional, candidate genes for keratoconus are being discovered at a rapid pace, the molecular genetic mechanisms underlying keratoconus pathogenesis will advance our understanding of keratoconus and promote the development of a novel therapy.

Association of polymorphisms in the hepatocyte growth factor gene promoter with keratoconus

PURPOSE

Keratoconus is a progressive disorder of the cornea that can lead to severe visual impairment or blindness. Although several genomic regions have been linked to rare familial forms of keratoconus, no genes have yet been definitively identified for common forms of the disease.

METHODS

Two genome-wide association scans were undertaken in parallel. The first used pooled DNA from an Australian cohort, followed by typing of top-ranked single-nucleotide polymorphisms (SNPs) in individual DNA samples. The second was conducted in individually genotyped patients, and controls from the USA. Tag SNPs around the hepatocyte growth factor (HGF) gene were typed in three additional replication cohorts. Serum levels of HGF protein in normal individuals were assessed with ELISA and correlated with genotype.

RESULTS

The only SNP observed to be associated in both the pooled discovery and primary replication cohort was rs1014091, located upstream of the HGF gene. The nearby SNP rs3735520 was found to be associated in the individually typed discovery cohort (P = 6.1 × 10(-7)). Genotyping of tag SNPs around HGF revealed association at rs3735520 and rs17501108/rs1014091 in four of the five cohorts. Meta-analysis of all five datasets together yielded suggestive P values for rs3735520 (P = 9.9 × 10(-7)) and rs17501108 (P = 9.9 × 10(-5)). In addition, SNP rs3735520 was found to be associated with serum HGF level in normal individuals (P = 0.036).

CONCLUSIONS

Taken together, these results implicate genetic variation at the HGF locus with keratoconus susceptibility.

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.