What is hereditary cobalamin malabsorbtion (HCM)?
Dogs with HCM cannot absorb vitamin B12 in the gut. Cobalamin malabsorbtion can be secondary to (caused by) other diseases but the primary form is hereditary. Symptoms are highly varied and can mimic many other diseases including exocrine pancreatic insufficiency, porto-systemic (liver) shunt, and early-onset intractable epilepsy. Severity of the disease is also highly variable; in the worst cases it can be fatal. Treatment is relatively simple and inexpensive: periodic Vitamin B12 shots.
How is HCM inherited?
HCM is caused by a single gene and has recessive inheritance. If a dog has HCM both of its parents carry the mutation that causes it. Dogs affected with HCM should not be bred. There is a DNA test available so siblings of the affected dog and the grandparents should be tested if they are to be bred. Those which have the mutation and the parents, which must have it, should be bred only to clear-tested dogs.
What dogs need to be tested?
Any dog that is a first-step relative of an affected dog or carrier dog should be tested. First step relatives are full- and half-siblings, parents, and offspring which may be used for breeding. If testing reveals relatives that have the mutation, their remaining first-step relatives would require testing. Example: If a dog is an HCM carrier it’s parents, full siblings and any offspring it may have which are breeding dogs should be tested. Once the carrier parent of that dog is identified, the half-sibs from that parent who are to be bred should also be tested.
How do I get my dog tested and what do results tell me?
As of this writing (2019) there are two labs in the US that offer a DNA test for HCM: the University of Pennsylvania’s lab, PennGen and Paw Print Genetics. The Paw Print test is for an Aussie-specific mutation. If you are in another country, you will need to survey the canine DNA testing labs available to you to see if they offer it.
Results will indicate whether your dog has one, two, or no copies of the mutated version of the HCM gene. Dogs with two copies are affected and should not be bred. If the dog’s illness was not already noted (some are only slightly affected) it should be brought to the attention of the dog’s veterinarian and the need for injectable B12 supplementation discussed. If your dog has one copy of the mutation it is a carrier for HCM and should be breed only to clear-tested mates. If your dog does not have the mutation it is clear of HCM.
Are exocrine pancreatic insufficiency (EPI) and cobalamin malabsorbtion the same thing?
No, though they are both metabolic diseases. In EPI the pancreas isn’t functioning properly. A dog with hereditary (primary) cobalamin malabsorbtion cannot absorb vitamin B12 through its gut. Symptoms of these two very different diseases can overlap and dogs with EPI may have secondary cobalamin malabsorbtion. Misdiagnosis isn’t unusual for either disease because both have varied symptoms that can mimic other diseases. In addition, many vets aren’t aware of that cobalamin malabsorbtion may be hereditary so don’t know to test for it. (There is a DNA test available.) EPI is uncommon in Aussies, cobalamin malabsorbtion may not be.