Vitamin D-Dependent Rickets Type II

Vitamin D-dependent rickets type II is a bone disorder characterized by brittleness and softening of the bones due to deficient calcium absorption. This condition results from a mutation in the VDR gene, responsible for encoding the vitamin D receptor.

Symptoms

Puppies affected by this bone condition show symptoms from the first months of life. These symptoms include muscle weakness, pain and difficulty in moving, as well as bowing of the limbs. In addition, they may experience spontaneous fractures, alopecia and secondary hyperparathyroidism.

Disease Management

There are no specific preventive measures for this condition. Treatment is based on the administration of vitamin D analogs and calcium supplements to correct the underlying deficiency. The dosage and frequency of supplementation will vary according to the severity of the disease. If you suspect your dog may be affected, it is crucial to see your veterinarian for an accurate diagnosis and treatment.

Genetic basis

This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the dog, regardless of sex, must receive two copies of the mutation or pathogenic variant to be at risk of developing the disease. Both parents of an affected dog must carry at least one copy of the mutation. Animals with only one copy of the mutation are not at increased risk of developing the disease, but may pass the mutation on to future generations. Breeding between dogs carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

Vitamin D plays an essential role in the absorption and utilization of calcium, which is necessary for bone formation and maintenance. In vitamin D-dependent rickets type II, a rare disorder, there is an inability to respond to the active form of vitamin D, which affects calcium absorption and leads to bone weakness. This disease is caused by a mutation in the VDR gene, which encodes the vitamin D receptor. The c.462del variant is a deletion in exon 4 that generates a reading frame shift and introduces a premature stop codon. As a result, the vitamin D receptor encoded by the VDR gene cannot respond to active vitamin D (1,25-Dihydroxyvitamin D).

Most affected breeds

Pomeranian

Bibliography

LeVine DN, Zhou Y, Ghiloni RJ, et al. 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. 2009 Nov-Dec;23(6):1278-83.