Nephritis, X-linked, in Samoyeds

Nephritis is an inflammatory disease of the kidneys. It is manifested by the presence of protein in the urine (proteinuria) and rapidly progressive kidney failure, which is fatal. Affected dogs usually die by one year of age.

In Samoyeds, the disease is caused by a nonsense mutation in type IV collagen genes, a key component of the basement membrane of the glomeruli. Specifically, the c.3079G>T substitution in the COL4A5 gene results in premature stop codon generation. Affected dogs have significantly reduced levels of type IV collagen chains 3, 4 and 5, which is manifested by deformation of the glomerular basement membrane. In addition, the mutation leads to deformities of the lens of the eye and reduced tension on the basement membrane of the Organ of Corti in the inner ear.

The mutation is X-linked. This means that it is localized on the X chromosome. Males have an X and a Y chromosome, so they can only be healthy (Xn/Y) or affected (Xm/Y). Females have two X chromosomes, so they can either be healthy (Xn/Xn), carriers (Xn/Xm) or affected (Xm/Xm). Female carriers do not show clinical signs but are able to pass the mutant allele to their offspring. Breeding of carrier females is not recommended. The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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References:

Zheng, K.Q., Thorner, P.S., Marrano, P., Baumal, R., Mcinnes, R.R.: Canine X chromosome-linked hereditary nephritis - A genetic model for human X-linked hereditary nephritis resulting from a single base mutation in the gene encoding the alpha 5 chain of collagen type IV. Proceedings of the National Academy of Sciences of the United States of America 91:3989-3993, 1994. Pubmed reference: 8171024