Abstract
Canine progressive retinal atrophy (PRA) describes a group of hereditary diseases characterized by photoreceptor cell death in the retina, leading to visual impairment. Despite the identification of multiple PRA-causing variants, extensive heterogeneity of PRA is observed across and within dog breeds, with many still genetically unsolved. This study sought to elucidate the causal variant for a distinct form of PRA in the Shetland sheepdog, using a whole-genome sequencing approach. Filtering variants from a single PRA-affected Shetland sheepdog genome compared to 176 genomes of other breeds identified a single nucleotide variant in exon 11 of the Bardet–Biedl syndrome-2 gene (BBS2) (c.1222G>C; p.Ala408Pro). Genotyping 1386 canids of 155 dog breeds, 15 cross breeds and 8 wolves indicated the c.1222G>C variant was only segregated within Shetland sheepdogs. Out of 505 Shetland sheepdogs, seven were homozygous for the variant. Clinical history and photographs for three homozygotes indicated the presence of a novel phenotype. In addition to PRA, additional clinical features in homozygous dogs support the discovery of a novel syndromic PRA in the breed. The development and utilization of a diagnostic DNA test aim to prevent the mutation from becoming more prevalent in the breed.
Highlights
Inherited retinal degenerations (IRDs) represent a group of hereditary diseases associated with reduced retinal function, leading to visual impairment and eventually blindness
This study aimed to identify the genetic cause of a novel form of progressive retinal atrophy (PRA) in the Shetland sheepdog (SS), to both improve
PRA was diagnosed based on bilateral retinal degeneration findings due to tapetal hyperreflectivity with retinal vascular attenuation and a pale optic disc
Summary
Inherited retinal degenerations (IRDs) represent a group of hereditary diseases associated with reduced retinal function, leading to visual impairment and eventually blindness. In the domestic dog (Canis familiaris), progressive retinal atrophy (PRA) describes a group of heterogeneous IRDs characterized by depletion of rod and cone photoreceptor cells in the retina over time. Clinical signs of PRA include the attenuation of retinal blood vessels, widespread hyperreflectivity of the tapetum due to retinal thinning and atrophy of the optic disc, revealing the presence of bilateral retinal degeneration. PRA affects many dog breeds and is considered a welfare concern as vision loss is inevitable. Canine PRA is akin to human retinitis pigmentosa (RP) that affects 1 in 4000 humans worldwide [1], and shares phenotypic similarities
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