Glycogen Storage Disease type IV of the Norwegian Forest Cat:
GSD IV (Glycogen Storage Disease type IV) is an inherited disorder affecting the glucose metabolism. This inherited deficiency is known in humans, horses and cats, but among cats it has only been seen in the Norwegian Forest Cats.
Most affected kittens are stillborn or die soon after birth, presumably due to hypoglycaemia (not being able to produce enough glucose "energy") during the birth process and the first hours of life. In very rare cases affected kittens may develop "normally" until 4-5 months of age, they might get some intermittent fever (fever that rises and falls) with tremors and ataxia (lack of control of the movements), then the growth stops and the disease leads progressively to neuromuscular degeneration, to severe muscular weakness, contractions, atrophy and inability to use its limbs (especially the hind legs), to eat, clean itself, to cardiac failures or coma and finally to death before the age of 15 months. But the kitten has presumably already been put to sleep before that age in view of the terrible sufferance.
Mutation and Inheritance
The gene responsible for the disease has been identified by Dr. John Fyfe in the USA, who also developed a gene test for the mutation in Norwegian Forest Cats in 1996. In Europe this test has been available since 2007. The disease prevalence reported is around 15% in the USA, while statistics in Europe after testing around 2300 cats during a year show 12% carriers.
GSD IV is inherited as a simple autosomal recessive trait, which means that both parents must be carriers of the mutated gene in order to produce affected offspring.
* Homozygous mutated cats should not be used for breeding. However, these cats generally die before becoming sexually mature and consequently don't pose any problem for selection as they are automatically removed from reproduction.
* Heterozygous carrier cats can be used for breeding, but they should then only be bred to partners who do not carry the mutation, as proven by gene testing. Kittens from such a litter should be tested before sold as future breeding cats. Ideally only homozygous negative kittens should be used for breeding, but exceptions can be made as long as the buyer of the kitten is well aware of the problem and will continue to follow these recommendations.
* All buyers of carrier kittens and kittens of unknown status from combinations where both parents are not negative should be informed about the disease, the fact that a parent is a carrier, and the risks of using the kitten for breeding. Heterozygous carriers will never get any symptoms, so one might think it is irrelevant information for a pet buyer. However, since it isn't uncommon that pet buyers later get the idea to have a litter from their cat, and they might then go ahead without contacting the breeder of the cat, it is important that also pet buyers fully understand the nature of the disease and the situation with their kitten.
* The aim should be to have eliminated all carrier cats from breeding by the year 2015.
How do I test my Cat?
The DNA sample is taken by your veterinary, with special cytobrushes and collected in a tube with ethanol (test kits can usually be ordered from the labs free of charge). The veterinary should fill in the sampling form with info on owner and the identification of the animal. The form and the sample are then sent to the laboratory. You also have to make a bank transfer for the payment. Then you will receive the results in a few weeks.