Testing of dogs: CSNB

CSNB - Congenital Stationary Night Blindness

A specify eye defect is known among dogs Briard breed. This eye disease is called Congenital Stationary Night Blindness (CSNB). CSBN is inherited as an autosomal recessive trait. Eye disruption differs among dog individuals - from normal day vision to day blindness (Narfström et al., 1994).

CSNB disease expresses oneself slow retina degeneration in dog age about six months. First symptom is night blindness, day vision remains normal. During dog life CSNB disease can develop to total blindness. Defect could be clinically recognized in moment of its outbreak. It is not possible to find out when the disease outbreaks. Disease carriers cannot be clinically recognized. It can be found out by genetics test only!

In exon 5 of RPE65 gene (retina pigment epithelium-specific protein, 65 kDa) a deletion AAGAdel487-490 was found (Aguirre et al., 1998; Veske et al., 1999). This deletion induces CSNB eye defect. 4-bp deletion (AAGA) causes a frame shift and formation of a stop codon during retina pigment epithelium-specific protein translation.

CSNB defect is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P genotype only.  The dogs with P/N genotype are considered carriers of the disease (heterozygotes) - they have no clinical symptoms; they transfer the defect to their offspring. In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

In Czech Republic the appearance of CSNB was investigated (Bechyňová et. al. 2006). Ninety-five Briard dogs were tested for RPE 65 gene deletion. One mutated homozygote, twelve carrier heterozygotes and eighty-two healthy homozygous dogs were found. These correspond to frequencies - 0,863 healthy homyzygotes, 0,126 carriers and 0,011 mutated homozygotes.

References:
Aguirre G. D., Baldwin, V., Pearce-Kelling, S., Narfström, K., Ray, K., Acland, G. M. Congenital stationary night blindness in the dog: common mutation in the RPE65 gene indicates founder effect. Molecular Vision 1998; 4:23-29.
Narfström, K., Wrigstad, A., Nilsson, S. E.The Briard dog: A new animal model of congenital stationary night blindness. Ophthalmology 1998; 73:750-756.
Veske, A., Nilsson, S., Narfström, K., Gal, A. Retinal dystrophy of Swedish Briard / Briard-Beagle dogs is due to a 4-bp deletion in RPE65. Genomics 1999; 57:57-61.
Bechyňová R., Dostál J., Stratil A., Jílek F. Kongenitální stacionární noční slepota (CSNB) v populaci psů plemene briard v České Republice. Acta fytotechnica et zootechnica 2006;193-194