Gene Structure of the 10q26 Locus: A Clue to Cracking the ARMS2/HTRA1 Riddle?

Exploring the contribution of ARMS2 and HTRA1 genetic risk factors in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe irreversible central vision loss in individuals over 65 years old. Genome-wide association studies (GWASs) have shown that the region at chromosome 10q26, where the age-related maculopathy susceptibility (ARMS2/LOC387715) and HtrA serine peptidase 1 (HTRA1) genes are located, represents one of the strongest associated loci for AMD. However, the underlying biological mechanism of this genetic association has remained elusive. In this article, we extensively review the literature by us and others regarding the ARMS2/HTRA1 risk alleles and their functional significance. We also review the literature regarding the presumed function of the ARMS2 protein and the molecular processes of the HTRA1 protein in AMD pathogenesis in vitro and in vivo, including those of transgenic mice overexpressing HtrA1/HTRA1 which developed Bruch's membrane (BM) damage, choroidal neovascularization (CNV), and polypoidal choroidal vasculopathy (PCV), similar to human AMD patients. The elucidation of the molecular mechanisms of the ARMS2 and HTRA1 susceptibility loci has begun to untangle the complex biological pathways underlying AMD pathophysiology, pointing to new testable paradigms for treatment.

Associations of ARMS2 and NR3C2 genes polymorphisms with central serous chorioretinopathy in a Greek population

BACKGROUND

Central serous chorioretinopathy (CSCR) is characterized by serous detachment of the central neurosensory retina and it is one of the most common retinal disorders. Various genetic polymorphisms have been associated with CSCR development.

METHODS

The aim of our study was to investigate the potential association between ARMS2 (rs10490924) and NR3C2 (rs2070951 and rs5522) genes polymorphisms and CSCR development in a well defined Greek cohort for the first time in literature. We enrolled, in our case-control study, 48 CSCR patients and 137 controls. The ARMS2 (rs10490924) and NR3C2 (rs2070951 and rs5522) genes polymorphisms were analyzed using Polymerase Chain Reaction (PCR) assays.

RESULTS

In our study, we found significant associations between ARMS2rs10490924 and NR3C2rs2070951 single nucleotide polymorphisms and CSCR development. Specifically, the GTrs10490924 genotype frequency of the ARMS2 gene was found to be significantly associated with risk of CSCR and T allele of rs10490924ARMS2 gene was also found to increase risk for CSCR. The genotype frequency GC and CC of rs2070951NR3C2 gene were observed more frequently in CSCR patients than controls and C allele of rs2070951NR3C2 gene was also observed more frequently in CSCR patients than controls. Rs5522 of NR3C2 gene polymorphism was not found to be significantly associated with CSCR.

CONCLUSION

Our findings showed, for the first time in a Greek population, that SNPs in the ARMS2 and NR3C2 genes are significantly associated with risk of CSCR. The results of this study support the involvement of extracellular matrix (ARMS2 gene) and mineralocorticoid receptor (MR) in the pathogenesis of CSCR.

10q26 - The enigma in age-related macular degeneration

Despite comprehensive research efforts over the last decades, the pathomechanisms of age-related macular degeneration (AMD) remain far from being understood. Large-scale genome wide association studies (GWAS) were able to provide a defined set of genetic aberrations which contribute to disease risk, with the strongest contributors mapping to distinct regions on chromosome 1 and 10. While the chromosome 1 locus comprises factors of the complement system with well-known functions, the role of the 10q26-locus in AMD-pathophysiology remains enigmatic. 10q26 harbors a cluster of three functional genes, namely PLEKHA1, ARMS2 and HTRA1, with most of the AMD-associated genetic variants mapping to the latter two genes. High linkage disequilibrium between ARMS2 and HTRA1 has kept association studies from reliably defining the risk-causing gene for long and only very recently the genetic risk region has been narrowed to ARMS2, suggesting that this is the true AMD gene at this locus. However, genetic associations alone do not suffice to prove causality and one or more of the 14 SNPs on this haplotype may be involved in long-range control of gene expression, leaving HTRA1 and PLEKHA1 still suspects in the pathogenic pathway. Both, ARMS2 and HTRA1 have been linked to extracellular matrix homeostasis, yet their exact molecular function as well as their role in AMD pathogenesis remains to be uncovered. The transcriptional regulation of the 10q26 locus adds an additional level of complexity, given, that gene-regulatory as well as epigenetic alterations may influence expression levels from 10q26 in diseased individuals. Here, we provide a comprehensive overview on the 10q26 locus and its three gene products on various levels of biological complexity and discuss current and future research strategies to shed light on one of the remaining enigmatic spots in the AMD landscape.

The Phenotypic Course of Age-Related Macular Degeneration for ARMS2/HTRA1: The EYE-RISK Consortium

PURPOSE

Age-related maculopathy susceptibility 2 (ARMS2) is considered the most enigmatic of the genes for age-related macular degeneration (AMD). We investigated the phenotypic course and spectrum of AMD for the risk haplotype at the ARMS2 and high-temperature requirement A serine peptidase 1 (HTRA1) locus in a large European consortium.

DESIGN

Pooled analysis of 4 case-control and 6 cohort studies.

PARTICIPANTS

Individuals (N = 17 204) aged 55 years or older participating in the European Eye Epidemiology consortium.

METHODS

Age-related macular degeneration features and macular thickness were determined on multimodal images; data on genetics and phenotype were harmonized. Risks of AMD features for rs3750486 genotypes at the ARMS2/HTRA1 locus were determined by logistic regression and were compared with a genetic risk score (GRS) of 19 variants at the complement pathway. Lifetime risks were estimated with Kaplan-Meier analyses in population-based cohorts.

MAIN OUTCOME MEASURES

Age-related macular degeneration features and stage.

RESULTS

Of 2068 individuals with late AMD, 64.7% carried the ARMS2/HTRA1 risk allele. For homozygous carriers, the odds ratio (OR) of geographic atrophy was 8.6 (95% confidence interval [CI], 6.5-11.4), of choroidal neovascularization (CNV) was 11.2 (95% CI, 9.4-13.3), and of mixed late AMD was 12.2 (95% CI, 7.3-20.6). Cumulative lifetime risk of late AMD ranged from 4.4% for carriers of the nonrisk genotype to 9.4% and 26.8% for heterozygous and homozygous carriers. The latter received the diagnosis of late AMD 9.6 years (95% CI, 8.0-11.2) earlier than carriers of the nonrisk genotype. The risk haplotype was not associated with hard or soft drusen < 125 μm (OR, 1.2; 95% CI, 0.9-1.7), but risks increased significantly for soft drusen ≥ 125 μm (OR, 2.1; 95% CI, 1.5-3.0), up to an OR of 7.2 (95% CI, 3.8-13.8) for reticular pseudodrusen. Compared with persons with a high GRS for complement, homozygous carriers of ARMS2/HTRA1 showed a higher risk of CNV (OR, 4.1; 95% CI, 3.2-5.4); risks of other characteristics were not different.

CONCLUSIONS

Carriers of the risk haplotype at ARMS2/HTRA1 have a particularly high risk of late AMD at a relatively early age. Data suggest that risk variants at ARMS2/HTRA1 act as a strong catalyst of progression once early signs are present. The phenotypic spectrum resembles that of complement genes, only with higher risks of CNV.

Bringing the age-related macular degeneration high-risk allele age-related maculopathy susceptibility 2 into focus with stem cell technology

Age-related macular degeneration (AMD) is a major cause of blindness in older adults in developed countries. It is a multifactorial disease triggered by both environmental and genetic factors. High-temperature requirement A serine peptidase 1 (HTRA1) and age-related maculopathy susceptibility 2 (ARMS2) are two genes that are strongly associated with AMD. Because ARMS2 is an evolutionarily recent primate-specific gene and because the ARMS2/HTRA1 genes are positioned at a locus on chromosome 10q26 in a region with strong linkage disequilibrium, it is difficult to distinguish the functions of the individual genes. Therefore, it is necessary to bring these genes into focus. Patient-specific induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) provides direct access to a patient's genetics and allows for the possibility of identifying the initiating events of RPE-associated degenerative diseases. In this paper, a review of recent epidemiological studies of AMD is offered. An argument for a definite correlation between the ARMS2 gene and AMD is presented. A summary of the use of ARMS2 genotyping for medical treatment is provided. Several ARMS2-related genetic models based on such stem cells as iPSCs are introduced. The possibility of applying gene-editing techniques and stem-cell techniques to better explore the mechanisms of the ARMS2 high-risk allele, which will lead to important guidance for treatment, is also discussed.

Epigenetic Mechanisms of the Aging Human Retina

Degenerative retinal diseases, such as glaucoma, age-related macular degeneration, and diabetic retinopathy, have complex etiologies with environmental, genetic, and epigenetic contributions to disease pathology. Much effort has gone into elucidating both the genetic and the environmental risk factors for these retinal diseases. However, little is known about how these genetic and environmental risk factors bring about molecular changes that lead to pathology. Epigenetic mechanisms have received extensive attention of late for their promise of bridging the gap between environmental exposures and disease development via their influence on gene expression. Recent studies have identified epigenetic changes that associate with the incidence and/or progression of each of these retinal diseases. Therefore, these epigenetic modifications may be involved in the underlying pathological mechanisms leading to blindness. Further genome-wide epigenetic studies that incorporate well-characterized tissue samples, consider challenges similar to those relevant to gene expression studies, and combine the genome-wide epigenetic data with genome-wide genetic and expression data to identify additional potentially causative agents of disease are needed. Such studies will allow researchers to create much-needed therapeutics to prevent and/or intervene in disease progression. Improved therapeutics will greatly enhance the quality of life and reduce the burden of disease management for millions of patients living with these potentially blinding conditions.