Vitamin D-resistant Rickets, Type II

Rickets or rhachitis is a well-known bone disease caused by vitamin D deficiency. In this case, the cause of the disease is a mutation in the vitamin D receptor (VDR) gene. Even when there is sufficient vitamin D in the diet, the cells are unable to take it up and use it. The expressions of this condition include impaired bone formation (softening) and bone curvature. Vitamin D-resistant rickets in Pomeranians is caused by the c.462del mutation in the VDR gene.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

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.

.

References:

LeVine, DN., Zhou, Y., Ghiloni, RJ., Fields, EL., Birkenheuer, AJ., Gookin, JL., Roberston, ID., Malloy, PJ., Feldman, D. : Hereditary 1,25-dihydroxyvitamin D-resistant rickets in a Pomeranian dog caused by a novel mutation in the vitamin D receptor gene. J Vet Intern Med 23:1278-83, 2009. Pubmed reference: 19909429