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.

Department of Ophthalmology 1st Faculty of Medicine Charles University Prague and General University Hospital Prague U Nemocnice 2 Prague 128 08 Czech Republic

European Eye Clinic Lexum Antala Staška 1670 80 Prague 140 00 Czech Republic

Institute of Inherited Metabolic Disorders 1st Faculty of Medicine Charles University Prague and General University Hospital Prague Ke Karlovu 2 Prague 128 08 Czech Republic

Institute of Molecular Genetics Vídeňská 1083 Prague 142 20 Czech Republic

Moorfields Eye Hospital London EC1V 2PD UK

UCL Genetics Institute University College London London WC1E 6BT UK

UCL Institute of Ophthalmology University College London London EC1V 9EL UK

Weatherall Institute of Molecular Medicine University of Oxford John Radcliffe Hospital Oxford OX3 9DS UK

References provided by Crossref.org