Mutations in LOXHD1, a Recessive-Deafness Locus, Cause Dominant Late-Onset Fuchs Corneal Dystrophy

Abstract

Fuchs corneal dystrophy (FCD) is a genetic disorder of the corneal endothelium and is the most common cause of corneal transplantation in the United States. Previously, we mapped a late-onset FCD locus, FCD2, on chromosome 18q. Here, we present next-generation sequencing of all coding exons in the FCD2 critical interval in a multigenerational pedigree in which FCD segregates as an autosomal-dominant trait. We identified a missense change in LOXHD1, a gene causing progressive hearing loss in humans, as the sole variant capable of explaining the phenotype in this pedigree. We observed LOXHD1 mRNA in cultured human corneal endothelial cells, whereas antibody staining of both human and mouse corneas showed staining in the corneal epithelium and endothelium. Corneal sections of the original proband were stained for LOXHD1 and demonstrated a distinct increase in antibody punctate staining in the endothelium and Descemet membrane; punctate staining was absent from both normal corneas and FCD corneas negative for causal LOXHD1 mutations. Subsequent interrogation of a cohort of >200 sporadic affected individuals identified another 15 heterozygous missense mutations that were absent from >800 control chromosomes. Furthermore, in silico analyses predicted that these mutations reside on the surface of the protein and are likely to affect the protein's interface and protein-protein interactions. Finally, expression of the familial LOXHD1 mutant allele as well as two sporadic mutations in cells revealed prominent cytoplasmic aggregates reminiscent of the corneal phenotype. All together, our data implicate rare alleles in LOXHD1 in the pathogenesis of FCD and highlight how different mutations in the same locus can potentially produce diverse phenotypes.

Endothelial Cell Whole Genome Expression Analysis in a Mouse Model of Early-Onset Fuchs' Endothelial Corneal Dystrophy

“…13,14 The hypothesis that the misfolding or aggregation of proteins in FECD contributes to cellular stress and apoptosis induction in CECs has also been proposed in studies investigating other genes affected in late-onset FECD like SLC4A11 and LOXHD1. 20,21 Increased transcriptional regulation of other important stress-associated genes such as Ptgs2 (Cox2), Hmox1, Serpine1, and Sod3 (complete list in Table 3) was found in the corneal endothelium of mutant animals. Although these markers point at least in part to the presence of endothelial oxidative stress, we observed no down-regulation of the antioxidant defense system, which has been demonstrated by previous studies in human late-onset end-stage FECD specimens.…”

Fuchs Corneal Dystrophy

“…CLU is involved with protein folding and colocalizes to guttae, and pathogenic LOXHD1 alleles induce misfolded aggregates in corneal endothelial cells. 32 In a comparison of FCD corneas with keratoconus and normal controls, misfolded proteins were found to be increased in FCD. 64 Of 10 corneas with FCD and 9 corneas with non-FCD corneal dystrophy, all FCD corneas exhibited prominent rough endoplasmic reticulum, in contrast to only a third of non-FCD corneas.…”

“…Three-dimensional reconstruction of the LOXHD1 protein predicted that most mutations resided on the protein surface, likely affecting interaction with other proteins. 32 The fourth gene with an identified causal mutation, AGBL1, codes for ATP/GTP-binding protein-like 1. The cytosolic carboxypeptidase family, of which AGBL1 is a member, catalyzes deglutamylation of polyglutamylated proteins.…”

The pathophysiology of Fuchs' endothelial dystrophy – A review of molecular and cellular insights

“…Therefore, SLC4A11 mutations alter endothelial water pump function, but NaBC1 is not essential for endothelial and DM function. A missense mutation in LOXHD1, a gene encoding a protein found in the plasma membrane, leads to over-expression and aggregation of the protein in the endothelium and DM, which could cause cell toxicity and endothelial breakdown (Riazuddin et al, 2012). In summary, mutations in two transcription factors (TCF4/E2-2 and TCF8/ZEB-1), one collagen subunit (COL8A2), and two membrane proteins (LOXHD1 and SLC4A11/ NaBC1) have been found in FECD.…”