Phenotypic Characterizations and Genetic Study of Progressive Rod-Cone Degeneration in Poodles in Thailand

Abstract

Progressive rod-cone degeneration (PRCD) is one of several groups of inherited progressive retinal atrophy in dogs. This study aims to describe the characterization of phenotypic appearance and demonstrate the responsible gene mutation, including analysis of the allele frequency of PRCD in Poodle dogs in Thailand. All 10 Poodles with clinical signs of PRCD were identified by a history of progressive vision loss, an abnormal obstacle test, and fundic appearance. Genetic testing of PRCD gene mutation using the Polymerase Chain Reaction and Restriction Fragment Length Polymorphism technique was performed in all dogs. The result confirmed that all 10 dogs were affected. The affected Poodles had presented age at first examination at 8.9 ± 2.33 years. Typical findings of retinal changes were bilateral retinal degeneration with tapetal hyperreflectivity, retinal vessel attenuation and optic disc atrophy. The electroretinogram from 7 affected dogs revealed non-detectable wave amplitude and implicit time in the session of rod responses in all dogs whereas small wave amplitude of cone response was recorded in 4 dogs. Histopathological examination of an affected eye revealed the collapse of the nuclear and photoreceptor layers.  A prevalence of carriers in 50 Poodles was 12% while the allele frequency of mutant allele was 0.1. Genetic finding of PRCD in Poodles in Thailand corresponds to the previous report whereas the age onset of dogs presented from this disease and the age at complete blindness are much later than previously reported.