Associations of 6p21.3 Region with Age-related Macular Degeneration and Polypoidal Choroidal Vasculopathy

Whole-genome methylation profiling of the retinal pigment epithelium of individuals with age-related macular degeneration reveals differential methylation of the SKI, GTF2H4, and TNXB genes

Background

Age-related macular degeneration (AMD) is a degenerative disorder of the central retina and the foremost cause of blindness. The retinal pigment epithelium (RPE) is a primary site of disease pathogenesis. The genetic basis of AMD is relatively well understood; however, this knowledge is yet to yield a treatment for the most prevalent non-neovascular disease forms. Therefore, tissue-specific epigenetic mechanisms of gene regulation are of considerable interest in AMD. We aimed to identify differentially methylated genes associated with AMD in the RPE and differentiate local DNA methylation aberrations from global DNA methylation changes, as local DNA methylation changes may be more amenable to therapeutic manipulation.

Methods

Epigenome-wide association study and targeted gene expression profiling were carried out in RPE cells from eyes of human donors. We performed genome-wide DNA methylation profiling (Illumina 450k BeadChip array) on RPE cells from 44 human donor eyes (25 AMD and 19 normal controls). We validated the findings using bisulfite pyrosequencing in 55 RPE samples (30 AMD and 25 normal controls) including technical (n = 38) and independent replicate samples (n = 17). Long interspersed nucleotide element 1 (LINE-1) analysis was then applied to assess global DNA methylation changes in the RPE. RT-qPCR on independent donor RPE samples was performed to assess gene expression changes.

Results

Genome-wide DNA methylation profiling identified differential methylation of multiple loci including the SKI proto-oncogene (SKI) (p = 1.18 × 10⁻⁹), general transcription factor IIH subunit H4 (GTF2H4) (p = 7.03 × 10⁻⁷), and Tenascin X (TNXB) (p = 6.30 × 10⁻⁶) genes in AMD. Bisulfite pyrosequencing validated the differentially methylated locus cg18934822 in SKI, and cg22508626 within GTF2H4, and excluded global DNA methylation changes in the RPE in AMD. We further demonstrated the differential expression of SKI, GTF2H4, and TNXB in the RPE of independent AMD donors.

Conclusions

We report the largest genome-wide methylation analysis of RPE in AMD along with associated gene expression changes to date, for the first-time reaching genome-wide significance, and identified novel targets for functional and future therapeutic intervention studies. The novel differentially methylated genes SKI and GTF2H4 have not been previously associated with AMD, and regulate disease pathways implicated in AMD, including TGF beta signaling (SKI) and transcription-dependent DNA repair mechanisms (GTF2H4).

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0608-2) contains supplementary material, which is available to authorized users.

Association of IGFN1 variant with polypoidal choroidal vasculopathy

BACKGROUND

Polypoidal choroidal vasculopathy (PCV) and neovascular age-related macular degeneration (nAMD) share a similar phenotype but are different in their clinical manifestations, responses to treatment and prognosis. Whether PCV is a subtype of AMD or a distinct entity from nAMD remains unknown. Therefore, we performed a whole-exome sequencing based association analysis to compare the genetic architecture of PCV and nAMD in Han Chinese.

METHODS

Whole-exome sequencing analysis was performed on 21 nAMD cases, 20 PCV cases and 20 healthy controls. As a follow-up validation, 145 nAMD cases, 160 PCV cases and 193 controls were genotyped using the Sequenom MassARRAY platform (Sequenom, San Diego, CA, USA).

RESULTS

A novel variant, c.6196A>G in the IGFN1 gene, was significantly associated with only PCV (combined p = 7.1 × 10^-11 , odds ratio = 9.44), but not with nAMD (combined p = 0.683, odds ratio = 1.30). The minor allele G conferred an increased risk of PCV.

CONCLUSIONS

The findings of the present study indicate that, although some of the susceptibility loci are shared between PCV and nAMD, a unique genetic signature may decide the pathogenesis of PCV.

Risk factors and biomarkers of age-related macular degeneration

A biomarker can be a substance or structure measured in body parts, fluids or products that can affect or predict disease incidence. As age-related macular degeneration (AMD) is the leading cause of blindness in the developed world, much research and effort has been invested in the identification of different biomarkers to predict disease incidence, identify at risk individuals, elucidate causative pathophysiological etiologies, guide screening, monitoring and treatment parameters, and predict disease outcomes. To date, a host of genetic, environmental, proteomic, and cellular targets have been identified as both risk factors and potential biomarkers for AMD. Despite this, their use has been confined to research settings and has not yet crossed into the clinical arena. A greater understanding of these factors and their use as potential biomarkers for AMD can guide future research and clinical practice. This article will discuss known risk factors and novel, potential biomarkers of AMD in addition to their application in both academic and clinical settings.