Distribution of rare LOXL1 missense alleles, haplotypes and diplotypes suggests association with reduced risk of glaucoma-related exfoliation syndrome.

Abstract

Purpose: Common LOXL1 protein-altering variants are significant genetic risk factors for exfoliation syndrome (XFS) and the related secondary glaucoma (XFG). A rare LOXL1 missense allele has been associated with protective effects in a Japanese cohort, suggesting that other rare alleles may also exhibit protective effects. The goal of this study was to assess the contributions of rare LOXL1 variants to XFS/XFG risk in cases and controls from the United States. Methods: LOXL1 rare (minor allele frequency less than 1%) variants were identified from Humanexome BeadArray (Illumina) data for 1118 XFS/XFG cases and 3661 controls. Distribution of rare variants, haplotypes (defined using IMPUTE2) and diplotypes were examined using the Fisher exact test. Rare variant allele distribution was confirmed in an independent set of primary open angle glaucoma (POAG) controls and multi-ethnic datasets. Correlation of LOXL1 common allele homozygosity with disease risk used data from gnomAD (gnomad.broadinstitute.org) and an existing multi-ethnic meta-analysis. Results: Four rare LOXL1 missense alleles were identified, and all were more common in controls (combined P= 7.6E-4), with two of these located in a LOXL1 intrinsic disordered region (IDR) known to be involved in LOXL1 aggregation. Haplotypes that included the rare or minor variants were more common in controls compared to cases (OR= 0.33, P=1.7E-8). Heterozygous diplotypes were significantly associated with reduced risk overall (OR= 0.45 P= 1.7 E-89) with the largest effects observed for diplotypes with more than one heterozygous genotype (OR= 0.05, P= 1.0E-39). A homozygous diplotype was associated with increased disease risk (OR= 6.8, P= 4.7E-157) and homozygosity was correlated with disease risk for common LOXL1 variants across multi-ethnic populations (Pearson= 0.92, P<0.001). Conclusions: Using exome array data from XFS/XFG cases and controls from the United States, we identify 4 rare protective LOXL1 missense variants and show that the distribution of the corresponding haplotypes and diplotypes are associated with reduced risk of XFS/XFG. The diplotype results also demonstrate that LOXL1 allelic heterozygosity is protective while homozygosity is associated with increased disease risk. These results suggest that LOXL1 minor allele frequency variation among populations, with corresponding variation in genotype heterozgyosity and homozygosity, determines the XFS/XFG association effects and that genotypic effects may also impact protein aggregation involving intrinsic disordered regions.