Whole exome sequencing identifies key biological pathways in primary open-angle glaucoma

Abstract

Purpose : The majority of primary open-angle glaucoma (POAG) disease burden is currently unexplained with known Mendelian genes only accounting for around 5%. We hypothesize a significant proportion of the genetic burden is driven by rare variants in a large number of yet unidentified genes. This study explores the biological mechanisms in POAG by examining rare variants using whole exome sequencing of cases with the most severe phenotypes from the Australian and New Zealand Registry of Advanced Glaucoma.

Methods : 187 participants fulfilled inclusion criteria of having advanced POAG with a young age of diagnosis (mean = 44.4 yrs, SD = 10.4 yrs). Myocilin mutation carriers were excluded by direct sequencing. Whole exome sequencing was performed on glaucoma cases and local non-glaucoma controls (n = 103) then joint-called with exomes of 993 previously sequenced Australian Osteoporosis Genetics Consortium controls. Qualifying genetic variants were selected based on rarity in the general population (maf < 0.001), canonical loss of function and predicted pathogenicity by SIFT and Polyphen2. Cases were compared to controls and public Exome Aggregation Consortium data. Genes showing enrichment for rare variants in POAG, high pressure (HTG) and normal tension (NTG) subgroups were selected for pathway analysis using public databases through InnateDB with Benjamini Hochberg discovery rate correction.

Results : POAG showed significant enrichment of rare variants in camera-type eye development genes (p=5.36x10^-7, corrected=1.1x10^-3). Most implicated eye development genes were related to neuronal development. HTG was significantly enriched for key regulators in the unfolded protein response (UPR) pathway (p=1.21x10^-4, corrected=0.02). UPR is known to be involved in myocilin glaucoma; our results extend its importance to non-myocilin causes of HTG. NTG showed enrichment in ion channel transport processes (p=1.19x10^-4, corrected=0.03) including ATPases, GABA receptors and cation transporters involved in transmembrane potential maintenance.

Conclusions : POAG may arise from abnormalities in ocular development which increase susceptibility to disease later in life. HTG is significantly associated with a potential accumulation of misfolded proteins secondary to deficiencies in their neutralization. Mutations in ion channel transport genes significantly predispose to the development of NTG suggesting an excitotoxicity mechanism.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.