Glycogen Storage Disease Type IV in Norwegian Forest Cats

Norwegian Forest cats are known to be predisposed to developing Glycogen Storage Disease Type IV as it is a genetically inherited disease passed down from their parents. As I understand it, if both parents carry the genetic mutation which causes the disease, the offspring have a 25% chance of being affected. If one parent doesn't have the disease but the other is a carrier the resultant offspring will not be affected but will have a 50% chance of being a carrier.

Healthy NFC kittens. Image credit as stated.

The disease affects other animals such as horses. In horses, the frequency of the diseases 8.3% in Quarter Horses and 7.1% in Paint Horses. I could not find the level of prevalence of this disease in Norwegian Forest Cats. However, it is a known inherited disease as mentioned.

Another term for Glycogen Storage Disease Type IV is "glycogen branching enzyme deficiency". This is because the affected individuals lack the enzyme necessary to store glycogen in its branched form and therefore cannot store sugar molecules needed by the heart and skeletal muscle, liver and brain which causes these organs to malfunction. Glycogen is a storage sugar molecule.

The degeneration of the muscles and heart are apparent and evident in histological analysis. In one study they did not find cirrhosis and hepatic failure which are apparently hallmarks of the human version of this disorder.

The defective gene is autosomal i.e., not sex-linked and recessive. That's why both parents have to have the disease to pass it on to their offspring. As I understand it the first report of this disease in 'inbred' Norwegian Forest cats was published in a study which I'm referring to in 1992 (see base of article for the name of the study).

The disease affects offspring before birth and causes an accumulation an abnormal glycogen in many tissues. These can manifest itself in stillbirth or the death of the kitten in the hours after birth. The cause of death is the kitten having an insufficient amount of glucose to produce energy during the birth process and in the hours afterwards.

Sometimes kittens survive the neonatal period. They might appear normal until five months of age. Owners might have to watch their kitten go through months of generation of nerves and muscle. They may suffer from fever and muscle tremors, and certainly weakness. By eight months of age the affected kittens have an inability to use their limbs due to severe muscle weakness and atrophy. They may die suddenly from heart failure.

A DNA test is available to identify the gene and identify carrier cats. Clearly, they should be removed from any breeding programs.

Study: Glycogen Storage Disease Type IV: Inherited Deficiency of Branching Enzyme Activity in Cats published on the nature.com website.