Hereditary Vitamin D-Resistant Rickets Type II

Hereditary Vitamin D-Resistant Rickets (HVDRR) is a bone defect where vitamin D cannot be delivered to the bones effectively. This prevents normal bone mineralization, leading to softening and bending of the bones and skeletal problems.

Key Signs

Hypocalcemia, Secondary hyperparathyroidism, Hypomineralization of bones, Bone malformations, Rickets, Joint pain, Lameness, Limb deformities, Spontaneous fractures, Alopecia

Age of Onset

0 to 2 yrs

Juvenile onset

Inheritance

Autosomal Recessive

For autosomal recessive disorders, dogs with two copies of the variant are at risk of developing the condition. Dogs with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their puppies if bred.

Likelihood of the Condition

High likelihood

At risk dogs are highly likely to show signs of this disease in their lifetime.

What to Do

Here’s how to care for a dog with HVDRR

Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about HVDRR

HVDRR is characterized by low calcium levels leading to secondary hyperparathyroidism. Vitamin D enhances bone mineralization and calcium is essential for hardness and strength of the bones. Vitamin D-resistance causes dysfunctional bone mineralization leading to the softening of bones and skeletal deformities. The clinical signs of HVDRR include joint pain, lameness, limb deformities, spontaneous fractures, jaw deformities, and neurological signs. HVDRR can also cause alopecia (hairlessness).

As soon as a diagnosis of HVDRR has been confirmed affected dogs should be considered for treatment. Affected dogs can be treated by oral administration of active vitamin D and calcium supplements. The bone deformities are, however, irreversible.

For Breeders

Planning to breed a dog with this genetic variant?

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to occur. A carrier dog with one copy of the HVDRR mutation can be safely bred with a clear dog with no copies of the HVDRR mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the HVDRR mutation. Puppies in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected puppies. Please note: It is possible that disease signs similar to the ones caused by the HVDRR mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene	VDR
Variant	Deletion
Chromosome	27
Coordinate	6,895,068

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

LeVine, D. N., Zhou, Y., Ghiloni, R. J., Fields, E. L., Birkenheuer, A. J., Gookin, J. L., Roberston, I. D., Malloy, P. J., & Feldman, D. (2009). Hereditary 1,25-dihydroxyvitamin D-resistant rickets in a pomeranian dog caused by a novel mutation in the vitamin D receptor gene. Journal of Veterinary Internal Medicine. View the article

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