Mutations In The Recessive Deafness Locus Loxhd1 Cause Dominant Late-onset Fuchs Corneal Dystrophy

Abstract

Purpose: : Fuchs Corneal Dystrophy (FCD) is a common progressive disorder of the corneal endothelium that affects as much as 4% of the United States population over the age of 40 years. Previously, we localized late-onset FCD in three large families with multiple affected individuals to chromosome 18q but the causal lesion responsible for the disease phenotype in these three families is yet unknown. This study was designed to identify the genetic basis of late-onset FCD utilizing the next-generation sequencing by synthesis technology.

Methods: : We reassigned the proximal and distal boundaries of the FCD2 locus based on at least two recombination events at each end. Exonic regions of all UCSC genes along with 20 base pair of sequence from the 5` and 3` ends of these exons were designed on a 385K Nimblegen array. Targeted regions from one affected and an unaffected individual per family were captured, enriched, and pair-end sequenced on an Illumina IIx genome analyzer. The raw data were assembled by Eland algorithms and aligned to the chromosome 18 reference sequence by Seqmate software.

Results: : We identified a missense change in LOXHD1, a gene causing early onset recessive hearing loss,as the sole variant capable of explaining the phenotype in this pedigree. Subsequent interrogation of a cohort of >200 sporadic patients identified another 15 heterozygous missense mutations that were absent from >800 control chromosomes. We observed LOXHD1 mRNA in cultured human corneal endothelial cells, while antibody staining of both human and mouse corneas showed expression in the corneal epithelium and endothelium. Corneal sections of the original proband stained for LOXHD1 demonstrated a distinct increase in antibody punctate staining in the endothelium and Descemets membrane that were absent from both normal and FCD corneas negative for LOXHD1 alleles. Expression of the familial LOXHD1 mutant allele as well as two sporadic mutations in cells revealed prominent cytoplasmic aggregates reminiscent of the corneal phenotype.

Conclusions: : Our data implicate rare alleles in LOXHD1 in the pathogenesis of FCD and highlight how different mutations in the same locus can potentially drive diverse phenotypes.

Keywords: cornea: endothelium • gene mapping • genetics