Bardet-Biedl syndrome 4 in Puli

Bardet-Biedl syndrome is a specific form of progressive retinal atrophy (PRA). PRA is a large group of inherited diseases that are the leading cause of blindness in various breeds of dogs. Individuals affected by PRA show a similar sequence of clinical abnormalities during the disease. Symptoms begin with night blindness followed by progressive loss of daytime vision and eventual blindness in all light conditions. Routine ocular examinations reveal a progressive loss of retinal photosensitive cells (retinas) due to retinal degeneration or atrophy.

The disease is caused by a nonsense mutation c.58A>T in the BBS4 gene, which leads to a complete loss of function of the resulting protein.

BBS4 is a recessively inherited disease. The disease develops in dogs which inherit the mutated gene from each parent.  These dogs are designated as P/P (positive/positive). The carriers of the mutated gene are designated as N/P (negative/positive). The carriers inherited the mutated gene from one parent only and are without clinical signs. However, they pass the disease on to their offspring.  When mating two heterozygotes (N/P), there will be theoretically 25% of the offspring healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will be affected by BBS4.  Mating one healthy dog (N/N) with a carrier of this mutation (N/P) will theoretically produce 50% carriers and 50% healthy offspring.  If a carrier (N/P) is mated with an affected dog (P/P), there will be theoretically 50% affected dogs and 50% carriers.

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References:

Chew, T., Haase, B., Bathgate, R., Willet, C.E., Kaukonen, M.K., Mascord, L.J., Lohi, H.T., Wade, C.M. : A coding variant in the gene Bardet-Biedl syndrome 4 (BBS4) is associated with a novel form of canine progressive retinal atrophy. G3 (Bethesda) 7:2327-2335, 2017. Pubmed reference: 28533336