Novel VMD2 Mutation(s) in the Dog Model for Best Phenotypes in Human

Abstract

Purpose: : Mutations in the VMD2 gene are associated with various retinopathies in man and dog (cmr). The ability to pursue detailed molecular and clinical studies in the dog model to investigate disease mechanisms and potential therapeutic approaches for disorders related to mutations in the VMD2 gene, make the dog an important model organism to carry out these studies. To investigate the influence of bestrophin related retinopathies in the dog, and identify additional models for human disease, selected dogs with a retinal phenotype similar to cmr were screened for mutations in VMD2, and identified changes evaluated for disease association.

Methods: : DNA was isolated following standard protocols from blood or buccal swabs of Lapponian Herder dogs (LHs) from Finland with ascertained clinical diagnosis. Coding exons of VMD2 were amplified as previously described (Guziewicz et al., 2006), and sequences were aligned to published wild type.

Results: : LHs originating in Finland display a disease, formerly termed retinopathy, that is clinically identical to previously described canine multifocal retinopathy (cmr1, cmr2). Unlike other breeds with cmr, affected LHs carry two homozygous mutations in exon 10; a deletion leading to a frame shift (CFA18, bp 57499959, Cdel, Pro463FS), and a point mutation (CFA18, bp 57499881, G>T). The latter leads to a stop codon at aa 490 if coupled with the deletion, or a Gly489Val substitution in the absence of the deletion. Within the investigated pedigree, these two mutations are completely linked, and associated with the disease phenotype. Neither of the mutations was found in a screen of samples from dogs with retinal changes of 25 additional breeds from Finland.

Conclusions: : We describe an additional model, cmr3, in the Lapponian Herder breed. These results indicate that cmr has a larger impact on the general dog population then was initially thought, and will further contribute to ongoing studies to understand the molecular basis of mutations in VMD2 and define correlations of observed genotypes with the respective phenotypes.

Keywords: mutations • retinal pigment epithelium • candidate gene analysis