Autosomal-Dominant Corneal Endothelial Dystrophies CHED1 and PPCD1 Are Allelic Disorders Caused by Non-coding Mutations in the Promoter of OVOL2

Alice E Davidson ,Neyme Veli,Noriaki Sasai,Stanislav Kmoch,Zbyněk Kozmík,Martin Filipec,Vincent Plagnol,James Bellingham,Kateřina Hodaňová,Viktor Stránecký,Hana Hartmannová,Lenka Nosková,Nikolas Pontikos,Ľubica Ďuďáková ,Michael E Cheetham ,Petra Lišková ,Neil D Ebenezer ,Julie T Daniels ,Nwamaka Juliana Idigo ,Cerys J Evans ,Caroline Thaung ,Geoffrey J Maher ,Stephen Tuft ,Hannah J Levis ,Kateřina Jirsová ,Alison J Hardcastle

doi:10.1016/j.ajhg.2015.11.018

Abstract

Congenital hereditary endothelial dystrophy 1 (CHED1) and posterior polymorphous corneal dystrophy 1 (PPCD1) are autosomal-dominant corneal endothelial dystrophies that have been genetically mapped to overlapping loci on the short arm of chromosome 20. We combined genetic and genomic approaches to identify the cause of disease in extensive pedigrees comprising over 100 affected individuals. After exclusion of pathogenic coding, splice-site, and copy-number variations, a parallel approach using targeted and whole-genome sequencing facilitated the identification of pathogenic variants in a conserved region of the OVOL2 proximal promoter sequence in the index families (c.−339_361dup for CHED1 and c.−370T>C for PPCD1). Direct sequencing of the OVOL2 promoter in other unrelated affected individuals identified two additional mutations within the conserved proximal promoter sequence (c.−274T>G and c.−307T>C). OVOL2 encodes ovo-like 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. Interestingly, we did not detect OVOL2 expression in the normal corneal endothelium. Our in vitro data demonstrate that all four mutated OVOL2 promoters exhibited more transcriptional activity than the corresponding wild-type promoter, and we postulate that the mutations identified create cryptic cis-acting regulatory sequence binding sites that drive aberrant OVOL2 expression during endothelial cell development. Our data establish CHED1 and PPCD1 as allelic conditions and show that CHED1 represents the extreme of what can be considered a disease spectrum. They also implicate transcriptional dysregulation of OVOL2 as a common cause of dominantly inherited corneal endothelial dystrophies.

Highlights

Posterior polymorphous corneal dystrophy (PPCD) is an autosomal-dominant disease that primarily affects the corneal endothelium
We describe sequential genetic analyses that excluded copy-number variations (CNVs) and coding and/or splice-site mutations as the cause of Congenital hereditary endothelial dystrophy 1 (CHED1) or polymorphous corneal dystrophy 1 (PPCD1), and we identify the cause of disease via a parallel approach of genome sequence analysis
Clinical Characterization of CHED1 and PPCD1 The clinical and histological features of disease in family BR1 (Figure 1A) were first reported in 1969 as autosomaldominant congenital endothelial corneal dystrophy,[4] and further comments on selected individuals were provided in 1987.15 The condition was subsequently mapped to a 2.7 Mb region on 20p between markers D20S48 and

Summary

Introduction

Posterior polymorphous corneal dystrophy (PPCD) is an autosomal-dominant disease that primarily affects the corneal endothelium. PPCD is characterized by abnormal corneal endothelial cell morphology and associated Descemet membrane changes, which produce the appearance of vesicular lesions, gray-white opacities, and linear bands on clinical examination of the cornea.[1] The altered morphology is most likely congenital and either static or slowly progressive throughout life. In a minority of cases, these changes lead to a raised intraocular pressure with secondary glaucoma.[2,4,5] Up to 33% of PPCD subjects require corneal grafting to treat their corneal edema.[6,7]

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