Abstract
Purpose :
Superficial chronic corneal epithelial defects (SCCEDs) are spontaneous corneal defects in dogs that share many clinical and pathologic characteristics to recurrent corneal erosions in humans. Boxer dogs are known to be predisposed to SCCEDs, therefore a search for genetic defect was performed to explain this susceptibility.
Methods :
Whole blood samples were collected from 60 boxers, 40 with, and 20 without a known history of SCCEDs. DNA was extracted from blood followed by a genome wide association (GWAS) and whole genome sequencing (WGS) to find regions of interest and variants of high impact (missense, splice site) in genes believed to have importance corneal disease. Variants of interest were further evaluated with Sanger sequencing in a larger population of dogs. In a separate set of dogs with SCCEDs, total RNA was extracted from corneal tissue debrided from four affected NOG deletion Boxer dogs and four affected non-Boxer dogs without the deletion. RNA sequencing was done and differential gene expression analysis was performed. Finally, corneal samples from NOG WT and NOG deletion dogs with SCCEDs were stained for NOG, BMP 4 and 7, and TGFβ1 and 2.
Results :
GWAS analysis of 60 dogs identified 3 regions of statistical significance (p<5x10) on chromosomes 3, 10 and 19. There were no clear variants within the regions of most significance to the area identified by GWAS. However, WGS identified one variant, a 30 base pair deletion at a splice site in NOG (Chr 9:31453999) significantly associated (P<0.0001) with Boxers with SCCEDS compared to non-Boxers. However, the variant was also observed in Boxers without known SCCEDS. The variant had a calculated disease penetrance of 73%. Following sequencing of RNA from debrided corneas of NOG WT and NOG dogs with SCCEDs, NOG, BMP4, TGFβ2, and TGFβ-induced were all found to have significant fold reductions in expression in NOG. Corneal IHC from NOG deletion dogs with SCCEDs had lower NOG and TGFβ2 staining scores, but significantly higher scores of BMP2 and 7.
Conclusions :
Many Boxer dogs with SCCED have a genetic defect in noggin gene (NOG). NOG is a constitutive protein in the cornea which is a potent inhibitor of BMP, which likely regulate limbal epithelial progenitor cells (LEPC). Dysregulation of LEPC may play a role in the pathogenesis of recurrent corneal erosions.
This is a 2020 ARVO Annual Meeting abstract.