# Analysis of Selected Eye Disorders in a Group of Predisposed Breeds of Dogs: Molecular Diagnostics of Collie Eye Anomaly and Progressive Retinal Atrophy

## TL;DR

This study identifies genetic mutations causing eye disorders in dog breeds like Collies and Australian Shepherds, using molecular diagnostics to detect carriers and affected individuals.

## Contribution

The study confirms the utility of PCR-based testing for Collie Eye Anomaly and explores potential undetected carriers of PRA in related herding breeds.

## Key findings

- 31 dogs across four breeds carried the NHEJ1 gene mutation linked to Collie Eye Anomaly, with 15 being homozygous and 16 heterozygous.
- No mutations in the PDE6A gene associated with RCD3-type PRA were found in the studied samples.
- PCR-based genetic testing proved effective for early diagnosis and breed management of Collie Eye Anomaly.

## Abstract

Background: Two hereditary eye disorders that are frequently observed in Collies and related breeds are Collie Eye Anomaly (CEA) and Progressive Retinal Atrophy (PRA). The main symptom of CEA is choroidal hypoplasia. It is associated with a 7.8 kb deletion in intron 4 of the NHEJ1 gene located on chromosome CFA7. Rod–cone dysplasia 3 (RCD3), an early-onset form of PRA, is associated with mutations in the PDE6A gene. Methods: Molecular diagnostic techniques were used in this study to identify genetic mutations linked to CEA and RCD3-type PRA in a subset of dog breeds. Australian Shepherds (n = 29), Border Collies (n = 9), Longhaired Collies (n = 27), and Shetland Sheepdogs (n = 10) provided a total of 75 DNA samples. Samples were collected by buccal swab or blood draw, and PCR and real-time PCR methods were used for processing. Results: Of the dogs in the studied breeds, 31 had the NHEJ1 gene mutation linked to CEA. Among these, 15 were homozygous recessive (affected), while 16 were heterozygous (carriers). None of the samples had any mutations in the PDE6A gene associated with RCD3-type PRA. Conclusions: Effective identification of carriers and affected individuals for CEA was made possible by PCR-based genetic testing, confirming its value in early diagnosis and breed control. Although the RCD3 form of PRA has not been previously reported in Collies or Australian Shepherds, it was included in our analysis due to the genetic relatedness among herding breeds and the potential presence of undetected carriers resulting from historical crossbreeding.