Intestinal cobalamin malabsorption (border collie type) is an inherited disease affecting border collies. Affected dogs are unable to make adequate amounts of a protein that plays a role in absorption of certain nutrients from the intestinal tract and kidneys, including the B vitamin, cobalamin. Affected dogs have increased levels of methylmalonic acid in their urine (a sign of cobalamin deficiency) from as early as 14 weeks of age, but symptoms of disease may not be recognized by owners for months or years. Symptoms of disease include anorexia, lethargy, poor weight gain, poor muscle mass, and in rare circumstances, a severe neurological dysfunction called hepatic encephalopathy that can lead to altered mental state, seizures, coma and death. Affected dogs have an increase in certain proteins in their urine, and have decreased synthesis of blood cells resulting in Anemia and decreased numbers of neutrophils. Affected dogs require cobalamin supplementation for life that results in disease remission for most animals within a few weeks. Though not associated with clinical disease, affected dogs will continue to pass increased amounts of certain proteins in the urine even with cobalamin supplementation.
Breed-Specific Information for the Border Collie
The Mutation of the CUBN gene associated with intestinal cobalamin malabsorption (border collie type) has been identified in the border collie. Though the exact frequency in the overall border collie population is unknown, 6.3% out of 95 clinically normal border collies were found to be carriers of the mutation.
Genetic testing of the CUBN gene in border collies will reliably determine whether a dog is a genetic Carrier of intestinal cobalamin malabsorption (border collie type). Intestinal cobalamin malabsorption (border collie type) is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the CUBN gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Border collies that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Fyfe JC, Hemker SL, Venta PJ, Fitzgerald CA, Outerbridge CA, Myers SL, Giger U. An exon 53 frameshift mutation in CUBN abrogates cubam function and causes Imerslund-Grasbeck syndrome in dogs. Mol Genet Metab. 2013 Aug;109(4):390-6. doi: 10.1016/j.ymgme.2013.05.006. Epub 2013 May 22.