Form of progressive retinal atrophy due to cone-rod dystrophy (crd1) described in the American Staffordshire Terrier. Its molecular basis is confirmed: an in-frame deletion of three base pairs in the PDE6B gene, which causes early and rapidly progressive degeneration of cones and rods and progresses to blindness.

Form specific to the American Staffordshire Terrier. No verified carrier frequency estimates are available in the public literature.

- Reduced vision in bright light (early cone involvement)\n- Progressive attenuation of retinal vessels\n- Progressive tapetal hyperreflectivity\n- Night blindness and, in advanced stages, complete blindness\n- No ocular pain

crd1 was described in bull/terrier-type dogs in the early 2000s (Kijas et al., 2004). Goldstein et al. (2013), through an association study in a colony of American Staffordshire Terriers, mapped the locus to the telomeric end of CFA3 and identified as the causal variant an in-frame deletion in exon 21 of PDE6B (beta subunit of the rod cGMP phosphodiesterase). The genetic test derives from this characterisation.

- Test breeding animals before mating if a genetic test is available\n- Do not cross two carriers if the status is confirmed\n- A carrier can be crossed with a clear animal; test offspring intended for breeding\n- Complement with periodic ophthalmological examination to rule out other forms of PRA in the breed

The causal variant in PDE6B allows specific molecular diagnosis. The differential diagnosis includes other hereditary retinal degenerations; crd2 of the Pit Bull Terrier is caused by a variant in IQCB1, not in PDE6B. Electroretinography confirms the cone-rod pattern.

1. Kijas et al. (2004). Cloning of the canine ABCA4 gene and evaluation in canine cone-rod dystrophies and progressive retinal atrophies. Mol Vis 10:223-232. PMID: 15064680
2. Goldstein et al. (2013). IQCB1 and PDE6B mutations cause similar early onset retinal degenerations in two closely related terrier dog breeds. Invest Ophthalmol Vis Sci 54:7005-7019. PMID: 24045995
3. OMIA:001674-9615. Retinal atrophy - Cone-rod dystrophy 1 in Canis lupus familiaris (dog).