Autosomal dominant corneal endothelial dystrophies CHED1 and PPCD1 are allelic disorders caused by non-coding mutations in the promoter of OVOL2.

Abstract

Purpose : Congenital hereditary endothelial dystrophy 1 (CHED1) and posterior polymorphous corneal dystrophy 1 (PPCD1) are autosomal dominant inherited corneal endothelial disorders that have been genetically mapped to overlapping loci on chromosome 20p. We recruited extensive pedigrees, comprising over 100 affected individuals, with the aim of identifying the genetic cause(s) of disease.

Methods : Targeted and whole genome sequencing (WGS) was performed on multiple individuals from CHED1 and PPCD1 index families. The variant data were filtered according to allele frequency and potential pathogenicity. Candidate variants were directly sequenced for validation and segregation in the extensive pedigrees, and the promoter region of OVOL2 was directly sequenced as a candidate region in additional families. A dual luciferase reporter assay was used to assess the impact of disease-associated mutations on the activity of the OVOL2 promoter.

Results : Following exclusion of coding, splice-site and copy number variations, two unique variants in a conserved region of the OVOL2 promoter were identified, one segregating with CHED1, and another segregating with PPCD1 in the respective index families. Two further unique variants were identified in additional families by direct sequencing. The four unique mutations lie within a highly conserved 100 bp region of the OVOL2 proximal promoter. In vitro analysis using a dual luciferase reporter assay demonstrated that all four OVOL2 promoter mutations exhibited significantly (P≤0.001) increased transcriptional activity compared to the corresponding wild-type promoter sequence.

Conclusions : Our data establishes CHED1 and PPCD1 as allelic conditions, with CHED1 an extreme of what can be considered a disease spectrum, and implicates transcriptional dysregulation of OVOL2 as a common cause of dominantly inherited corneal endothelial dystrophies. OVOL2 encodes ovo-like 2 zinc finger 2, a C2H2 zinc finger transcription factor that regulates mesenchymal to epithelial transition, and acts as a direct transcriptional repressor of the established PPCD-associated gene, ZEB1. We postulate that the mutations identified introduce cryptic cis-acting regulatory sequence binding sites that drive aberrant OVOL2 expression during development of the corneal endothelium.

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