Test Overview:

Glycogen storage disease IV (GSD IV) is an autosomal recessive genetic disease, and affected kittens inherit an abnormal copy of the gene that causes the disease from both of their parents.  Both parents carry one copy of this gene, called GBE1, and are therefore carriers of the disease.  The carrier rates in the Norwegian Forest cat populations have been estimated at around 9-12% in Europe and 15% before testing began in the USA. GSD IV causes a deficiency in an enzyme called Glycogen Branching Enzyme (GBE), and this means affected animals cannot make normal glycogen.  Glycogen is how glucose is normally stored for use when it is needed in between meals.  Hence affected animals suffer from hypoglycaemia (low blood glucose) as well as damaged muscles due to the accumulation of abnormal glycogen.  Most (80%) of affected kittens are either still born, or die during or shortly after birth.  This is due to a severe lack of glucose causing coma and cardiac and/or respiratory failure.  The remaining 20% of affected kittens survive birth and develop what is known as the juvenile form of the disease. Development is more or less normal until 4-5 months of age, when kittens suddenly develop a fever and muscle weakness.  Kittens become weaker and weaker, and develop worsening muscle tremors.  Muscles atrophy (become wasted and small) and suffer contracture, so that affected kittens have great difficulty moving and eating.  Seizures will also develop due to hypoglycaemia.  This disease is always fatal, generally by 10-14 months of age.  Most cats are euthanased prior to this due to the bleak prognosis and suffering of the cat. Genetic testing is available in several laboratories for glycogen storage disease type IV.  Most labs have their own specific test, due to the complex genetics involved.  There is no cure for GSD IV, and treatment is palliative only.  Carrier cats should not be bred to one another - this is the only way to avoid producing kittens with this disease.