Breeds Affected: Pomeranian
Samples Accepted: Blood, Buccal Swabs
Disease Information: Dogs with HVDRR first show areas of hair loss (alopecia) and sparse hair overall compared to normal littermates. Pups tire easily and may how intermittent lameness and progressive bowing of the legs. Low calcium levels lead to bone weakness and breakage. Humane euthanasia may be necessary for quality of life reasons.
Inheritance Information: Vitamin D-resistant rickets, type II (HVDRR), is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/hvdrr The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/hvdrr carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
hvdrr/hvdrr The dog is affected, and if bred to a normal animal, 100% of the offspring will be carriers. If bred to an N/hvdrr carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/hvdrr x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/hvdrr x N/hvdrr) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (hvdrr/hvdrr) should not be used for breeding to avoid propagating the dwarfism phenotype.
Test Information: This test identifies a single base deletion in the gene VDR.
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. DOI: 10.1111/j.1939-1676.2009.0405.x
Further information is available at the Online Mendelian Inheritance in Animals website.