Imerslund-Grasbeck Syndrome


This year I was made aware of a genetic condition, which has been reported in Beagles. The condition is called Imerslund-Grasbeck Syndrome or IGS. IGS has also been reported in Border Collies, Australian Shepherds, Giant Schnauzers and Humans. This disease is concerned with Vitamin B12. Dogs cannot manufacture Vitamin B12 (also known as cobalamin), and rely on absorbing it from their diet using a protein molecule called intrinsic factor, which binds to the B12 and aids its transition across the gut lining.

A protein Cuban (shortened to CUBN) is in the lining of the intestine and binds with B12 and intrinsic factors allowing it to cross the lining into the bloodstream. It is faults with the CUBN that cause symptoms of IGS. There are small variations between Beagles and Border Collies with Beagles developing more severe malabsorption as they have a slightly different faulty gene. The disease reported in Giant Schnauzers and Australian Shepherds is a different part of intrinsic factor but results in the same symptoms due to lack of B12 absorption. All four breeds need a different DNA test to check out their status as different genes can be involved in different breeds of dogs and other species as they code for different parts of a protein called CUBN.

In Beagles it is inherited as a recessive condition (which means dogs have to have two copies of the gene to be affected), a single copy (carrier status) doesn’t result in the disease being expressed.

If two carriers are mated together then 25% of the puppies born can be affected as having two copies of the faulty gene. If either parent is clear then the disease is not seen as puppies can only be carriers or clear.

Vitamin B12 is important for many reasons in the dog including red blood cell production and development and maintenance of the nervous system. Without adequate B12 dogs rapidly develop macrocytic anaemia, poor weight gain, and poor growth and also start to show neurological signs as the nerve structure does not develop correctly. This is within a few weeks of birth as initially, they rely on stores built up during gestation, but without supplementation, such dogs will eventually die. Oral supplements are no good as the dog cannot absorb them so weekly injections are required to raise the blood levels to an adequate concentration, followed by regular blood tests to ensure the levels stay adequate and injections when they fall. This is a lifelong condition.

Initial symptoms are often vague, poor appetite, apparent stomach pain, rather poor looking puppies, and neurological signs and unless B12 levels are tested for it is hard to pinpoint what is going on. Many of the puppies affected have initially been thought to have a faulty liver or stomach/intestinal issue until the B12 levels are checked. In affected puppies, they are often only 1 % of what they should be. Injections of B12 rapidly make these puppies improve and if it is treated early enough they may come back to normal. Without adequate treatment, they eventually die.

There is a DNA test available to check the status of any beagles used for breeding. The test is available in several different labs around the world. So far the condition has been reported from three different continents so may be present in many different countries although not always recognized by vets and owners.