Bardet-Biedl syndrome 2 in Shetland Sheepdogs

Bardet-Biedl syndrome is a specific form of progressive retinal atrophy (PRA) in the dog. 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 throughout the course of 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 photosensitive cells (retinas) due to retinal degeneration or atrophy.

The disease is caused by a missense mutation c.1222G>C in the BBS2 gene.

BBS2 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 BBS2.  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:

Hitti-Malin, R.J., Burmeister, L.M., Lingaas, F., Kaukonen, M., Pettinen, I., Lohi, H., Sargan, D., Mellersh, C.S. : A Missense Variant in the Bardet-Biedl Syndrome 2 Gene (BBS2) Leads to a Novel Syndromic Retinal Degeneration in the Shetland Sheepdog. Genes (Basel) 12:1771, 2021. Pubmed reference: 34828377