Molecular test for CNGB1-associated progressive retinal atrophy (pap-PRA1) of the Papillon, a late-onset autosomal recessive hereditary retinal degeneration leading to progressive visual loss. It affects rod photoreceptors and progresses slowly, with vision relatively preserved for a long time. The test reports clear/carrier/affected status and allows matings to be planned while avoiding affected animals.

Described in the Papillon (and Phalène, the variety of the same breed). In a cohort of 145 Papillons/Phalènes the carrier frequency was 17.2%; the CNGB1 mutation was not detected in healthy dogs of 10 other breeds or in PRA-affected dogs of 44 other breeds (Ahonen 2013).

- Difficulty seeing in dim light (nyctalopia) of late onset
- Slow progression, with vision preserved for a long time
- Tapetal hyperreflectivity and vascular attenuation in the ocular fundus
- Pigmentary migration in the non-tapetal fundus
- Blindness in advanced stages (less frequent due to slow progression)

pap-PRA1 was molecularly characterized in 2013: two independent studies (Winkler et al.; Ahonen et al.) identified a frameshift mutation in the CNGB1 gene in the Papillon and the Phalène. Pedigree analysis indicated autosomal recessive inheritance; the mean onset was estimated at about 5.6 years.

- Genotype breeding animals before mating
- For a recessive condition: do not mate carrier×carrier (25% risk of affected homozygotes); carrier×clear produces 0% affected and 50% carriers
- An affected animal must not be bred; a carrier can be mated to a clear animal without producing affected offspring
- After a confirmed clinical case, do not repeat the parental mating and inform the buyer of the status

Annual ocular examination (ECVO) as a complement. Differentiate pap-PRA1 (CNGB1, late and slow onset) from other PRAs (prcd-PRA, cord1) by age of onset and ocular fundus. As a large part of Papillon PRAs is due to CNGB1, some forms remain to be characterized. Verify the exact locus offered by each laboratory.

1. Winkler PA et al. (2013) A large animal model for CNGB1 autosomal recessive retinitis pigmentosa. PLoS One 8(8):e72229. PMID: 23977260
2. Ahonen SJ et al. (2013) A CNGB1 frameshift mutation in Papillon and Phalène dogs with progressive retinal atrophy. PLoS One 8(8):e72122. PMID: 24015210
3. OMIA:002723-9615 (Retinal atrophy, progressive, CNGB1-related).