Naturskat Cattery

Norwegian Forest Cats

Announcement: Definitive carrier test for GSD lV of the Norwegian Forest Cats

John C. Fyfe, DVM, Ph.D., Assistant Professor of Microbiology, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824

Glycogen storage disease type lV (GSD lV) of the Norwegian Forest Cat is an inherited abnormality of glucose metabolism. Normally, excess glucose obtained in the diet or produced by conversion of proteins and fats is stored in many tissues as a very highly branched polymer (chain) of glucose residues called glycogen. A special biological catalyst called glycogen branching enzyme (GBE for short) is necessary during glycogen synthesis to produce the branching structure. When needed for energy, glucose molecules are removed from glycogen and digested within the tissue or released into the blood circulation for use by other tissues. The ability to add and remove glucose molecules from glycogen efficiently is dependent on its highly branched structure. Our studies have determined that GSD lV in Norwegian Forest Cats is due to an inherited deficiency of GBE. Affected kittens store a very abnormal glycogen, a glucose polymer devoid of branch points, in most tissues. 

The disease caused by GBE deficiency in Norwegian Forest Cats is of two types. By far, the most common form is still birth or death within a few hours of birth. We believe this to be due to insufficient glucose available to produce energy during the birth process and the first hours of life. On rare occasions an affected kitten will survive the neonatal period and appear normal until 5 months of age. Though less common this is the more devastating form of the disease because by this age new owners are very attached to their kitten, and they must witness it go through months of neuromuscular degeneration. By eight months of age, GSD lV results in severe muscular weakness and atrophy and contractures and inability to use the limbs. The cat may die suddenly from heart failure.

GSD lV is inherited as a simple autosomal recessive trait. Practically, this means that, though clinically-normal, both parents of an affected kitten are obligate carriers of the trait. The parents will pass their carrier status along to 50% of all their offspring, both male and female, when mated to a non-carrier cat. When two carriers are mated, 25% of the offspring will be affected and two- thirds of the clinically-normal littermates will be carriers. Because they are clinically-normal, carriers of GSD lV may be active breeders in a cattery, passing their carrier status along to the next generation, and never suspected until an affected kitten is born. Furthermore, because stillbirth or early death is not so uncommon for any of many reasons, a GSD lV affected kitten may be discarded without diagnosis and its carrier parents continue breeding unsuspected. One condition which can masquerade as neonatal death from GSD lV is neonatal isoerythrolysis (NI), a blood type-incompatibility problem which can cause death of newborn kittens a few hours after first nursing.

To overcome these problems we have developed a definitive, DNA-based carrier test that is not subject to the ambiguities we experienced previously when attempting to determine GBE activity in blood samples or muscle biopsies. This test will allow conscientious  Norwegian Forest Cat breeders to eliminate GSD lV carrier cats from their breeding programs while preserving desirable traits. The new carrier test detects directly whether the mutation that causes GSD lV is present in a cat's DNA in two copies, as in affected kittens, one copy, as in carriers, or not at all, as in genetically normal cats. In a preliminary study of just a few catteries, we have found several carriers; some were already known by having produced affected kittens,  but others were unsuspected. One cattery so far has used results of this test to identify non-carrier offspring of a favored and popular sire who was a known GSD lV carrier. These non-carrier offspring will carry on many desirable characteristics of the sire but not his disease carrier status.

We are now happy to make GSD lV carrier testing available to all who are interested through the Josephine Deubler Genetics Disease Testing Laboratory under the direction of Dr. Urs. Geiger, Chief of the Section of Medical Genetics at the University of Pennsylvania  School of Veterinary Medicine. For several years the Giger laboratory has offered feline blood typing services which have emerged as an important tool to prevent neonatal isoerythrolysis in kittens. The collaboration of Dr. Fyfe's laboratory at Michigan State University College of Veterinary Medicine, where the GSD lV test was developed, with Dr. Giger's will allow GSD lV testing and blood typing to be performed on the same samples, a real convenience to cat breeders. Dr. Fyfe has worked closely with Dr. Giger in the past and will remain a consultant to the testing laboratory regarding the GSD lV test.

A GSD lV carrier test and blood typing can be done at the same time. Ask how to proceed and pricing for the combined testing through the contact information below.*The required sample for both tests is 0.5-1.0ML of whole blood collected in sodium EDTA anticoagulant (a purple top tube). The samples would be transported to the laboratory within 2 days, preferably early in the week, but cooling is not necessary. The  express mail service available in all U.S. Post Office is is adequate. Each sample must be properly labeled with the cat's identification, and a written test request and payment must accompany each package of samples. 

*Questions regarding testing and proper collection and delivery of samples may be answered by calling the administrative office Susan Scheerban 215-898-8894  or email Urs Giger, PD Dr. med.vet.FVH Diplomate,  giger@vet.upenn.edu or regular mail to Dr. Giger School of Veterinary Medicine University of Pennsylvania 3850 Spruce Street, Philadelphia, Pa. 19104-6010. You may also call the lab 215-898-3375. 

 University of Pennsylvania site is located at

 http://w3.vet.upenn.edu/research/centers/penngen/services/deublerlab/gsd4.html

GSD lV Web Site

An independent web site has been set up to post cats that have been tested. This is very helpful to the owners of breeding cats that may be offspring of the tested cats.  Cats that are normal, non carriers are listed as normal/negative and cats that are carriers (affected and non-affected) are listed as carriers. This site is purely voluntary on the part of the breeders and has no affiliation with the laboratories performing the test.

This site will not contain those cats that may be known to be normal as a result of the parents being tested, if the offspring themselves are not tested.  Non-breeding healthy carriers and non-affected cats that have been altered may also not appear.

The site address is www.winterfyre.com/testing/