Generalised progressive retinal atrophy (PRA) with recessive inheritance in the Schapendoes. It affects the retinal photoreceptors: rods degenerate first, followed by cones, producing initial night blindness that progresses to complete blindness. A breed-specific genetic test is available that allows asymptomatic carriers to be identified.

It affects the Schapendoes. Limited data on the exact carrier frequency in the current breed population; the genetic test is the main tool for estimating it.

- Nyctalopia (night blindness) as the initial sign\n- Pupillary dilation\n- Tapetal hyperreflectivity\n- Retinal vessel attenuation\n- Progressive blindness up to complete vision loss

Generalised PRA of the Schapendoes was mapped by linkage analysis to a region of canine chromosome 20 (Lippmann et al., 2007; PMID 17327822). Sequencing of the CCDC66 gene, newly identified in that region, revealed a 1-bp insertion in exon 6 that generates a premature stop codon; the variant is homozygous in all affected dogs and heterozygous in all obligate carriers, confirming autosomal recessive inheritance (Dekomien et al., 2010; PMID 19777273). The murine model with the Ccdc66 gene knocked out reproduced the retinal degeneration and demonstrated the gene's role in photoreceptor development (Gerding et al., 2011; PMID 21680557).

- Genotype breeding animals before mating\n- Do not cross carrier×carrier (25 % risk of affected homozygotes); carrier×clear produces 0 % affected and 50 % carriers\n- An affected animal must not be bred; a carrier can be crossed with a clear dog without producing affected offspring\n- Annual ophthalmological examination (ECVO) complementary to the genetic test

The differential diagnosis includes other forms of PRA; the ophthalmoscopic picture is similar among them. Definitive confirmation requires genetic testing of CCDC66. The age of onset and the rate of progression may vary between individuals.

1. Lippmann T, et al. Haplotype-defined linkage region for gPRA in Schapendoes dogs. Mol Vis 2007;13:174-80. PMID: 17327822
2. Dekomien G, et al. Progressive retinal atrophy in Schapendoes dogs: mutation of the newly identified CCDC66 gene. Neurogenetics 2010;11(2):163-74. PMID: 19777273
3. Gerding WM, et al. Ccdc66 null mutation causes retinal degeneration and dysfunction. Hum Mol Genet 2011;20(18):3620-31. PMID: 21680557
4. OMIA:001521-9615 (CCDC66). https://omia.org/OMIA001521/9615/