Possibly relevant human trait(s) and/or gene(s)s (MIM numbers): 613464 (trait) , 615985 (trait) , 608132 (gene)

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal Recessive

Considered a defect: yes

Key variant known: yes

Year key variant first reported: 2014

Cross-species summary: Condition similar to Bardet-Biedl syndrome

Species-specific name: Golden Retriever PRA 2

Molecular basis: Downs et al. (2014) reported that "a single nucleotide deletion was identified in exon 8 of the TTC8 gene of affected Golden Retrievers. The frame shift mutation was predicted to cause a premature termination codon. In a larger cohort, this mutation, TTC8c.669delA, segregates correctly in 22 out of 29 cases tested (75.9%)." The authors concluded that "PRA is genetically heterogeneous in ... the Golden Retriever, and is caused by multiple, distinct mutations. ... PRA2 ... accounts for approximately 30% of PRA cases in the breed. The genetic explanation for approximately 9% of cases remains to be identified."

Clinical features: Progressive retinal atrophy results in bilateral degeneration of the retina. Affected dogs typically present with bilateral and progressive loss of vision and will eventually be completely blind. Clinical signs of PRA 2 typically begin to manifest at an average age of 5 years. Clinical examination in affected animals will show a hyper-reflective tapetum and retinal vessel attenuation. In later stages of the disease, dogs will show changes in pigment, pale optic discs and optic nerve atrophy (Downs et al., 2011).

Mäkeläinen et al. (2020): "The progression of PRA for two of the dogs was followed for 2 years ... . In addition to PRA, the dogs showed a spectrum of clinical and morphological signs similar to primary and secondary characteristics of human BBS patients, such as obesity, renal anomalies, sperm defects, and anosmia."

[IT thanks DVM student Rachel Simmonds for contributions to this entry in April 2022.]

Breed: Golden Retriever.

Associated gene: