Vitamin D-dependent rickets type II caused by a mutation in the vitamin D receptor gene (VDR) in the Pomeranian. It produces resistance to the action of vitamin D, altering calcium and phosphorus homeostasis and causing defective bone mineralization. It causes skeletal deformities, growth retardation and lameness in puppies.

Affects the Pomeranian. Limited data on the exact carrier frequency in the breed population.

- Bone deformities (bowing of the limbs)\n- Growth retardation\n- Pathological fractures\n- Hypocalcemia and elevated alkaline phosphatase\n- Bone pain and lameness

Vitamin D-dependent rickets due to a VDR mutation was characterized in the Pomeranian after observing a dog with skeletal deformities and compatible biochemical alterations (hypocalcemia, elevated alkaline phosphatase). LeVine and co-workers identified the causal deletion in the VDR gene in 2009, which enabled the development of a direct genetic test. It constitutes a veterinary model of human vitamin D-dependent hypocalcemic rickets (HVDRR/VDDR-II).

- Genotype breeding dogs before mating\n- Do not mate carrier×carrier (25% risk of affected homozygotes); carrier×clear produces 0% affected and 50% carriers\n- An affected animal should not be bred; a carrier can be mated to a clear dog without producing affected offspring\n- Affected puppies require veterinary management (calcium, active vitamin D) under supervision

The differential diagnosis includes nutritional rickets (dietary vitamin D deficiency) and X-linked hypophosphatemic rickets. Serum biochemistry (calcium, phosphorus, alkaline phosphatase, 25-OH-vitamin D, 1,25-(OH)2-vitamin D) guides the subtype: animals with a VDR mutation may have elevated levels of 1,25-(OH)2-vitamin D due to receptor resistance. Confirm with genetic testing for the VDR mutation.

1. LeVine DN et al. 2009, 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. PMID: 19909429. 2. Clarke KE et al. 2021, Vitamin D metabolism and disorders in dogs and cats. J Small Anim Pract. PMID: 34323302. OMIA:001431-9615.