Kittens

DISEASES

What is the Hypertrophic Cardiomyopathy or HCM ?

Hypertrophic Cardiomyopathy is a terminal condition where the heart muscle enlarges and thickens progressively over time. It can be a cause of sudden death, and symptoms may be mild or nonexistent. HCM in humans, in the majority of cases, is an inherited genetic disorder, with new mutations occurring frequently. The disease is caused by mutations in several genes and passed down to offspring by autosomal dominant inheritance. "Autosomal" means that the gender of the cat is of no importance, both males and females can be affected by the disorder. "Dominant" means that if a kitten has inherited the abnormal gene from one of its parents, it will develop the disease. With a recessive inherited disorder both father and mother have to pass down the abnormality to show the disease. Any cat regardless of breed can be afflicted with the disease. No cure is known at this time. If diagnosed early, medication (to both thin the blood and retard the growth of the heart wall) can slow the process down. Late diagnosis is usually post-mortem, or when the disease has reached an acute state.

Death by HCM can occur via three mechanisms: (1) sudden cardiac death with arrhythmia and ventricular fibrillation, (2) heart failure with tachycardia, increased respiration, shortness of breath, pulmonary oedema and pleural effusion or (3) thrombus formation. Thrombi can form either in the left atrium due to abnormal blood circulation or in the heart chamber itself due to severe hypertrophy and cardiac weakness. Atrial thrombi can brake free and reach the arterial blood circuit, thereby often causing blood congestion at the branching of pelvic and crural arteries with paralysis of the hind legs.

There is now HCM research going on in several countries; so far there is one DNA test available for the MyBPC3 mutation in Maine Coons. Research in the mutation(s) in Ragdolls is still going on and there is now talk about the (suspected?) recessive form of HCM occurring in Ragdolls. In most other breeds the HCM mutations seems to be more dominant, as far as known at this date (2007). Obviously the hope exists that a single mutation is present in all cats across the world. However this seems unlikely. It is more likely that there are many different mutations present within the feline population leading to the many different manifestations of the disease. The best hope for HCM, it seems at the moment, is to diagnose animals. And don't let them breed when afflicted with HCM. When not afflicted with HCM there is however no guarantee that the cat is free from HCM until the DNA tests are available and accurate.

Testing by scan is possible from an age of 10 months, only for indication. From the age of 2 years the heart of a male is full-grown and a female the heart is full-grown with 3 years. Certitude is 80%. when the test result is negative for HCM. But when the test result is positive for HCM the certitude is 100% . Equivocal means that anomalies have been observed but at the time of the testing, it is not clear what those anomalies mean or will mean. Not every cat who is assessed as equivocal, will develop HCM. On the other hand, the possibility does exist.

This exam is very expensive and for this reason, or because they do not see the point, many breeders don't practice the detection of HCM on their breeding cats.

Our breeding cats are tested by scan every 3 to 4 years.

What is the glycogen storage disease type IV or GSD IV ?

The glycogen storage disease type IV (GSD IV) is an inherited disorder of glucose metabolism. In Norwegian Forest Cat, GSD IV is due to an inherited deficiency of an enzyme of glycogen synthesis called GBE (Glycogen Branching Enzyme). In affected cats, an abnormal form of glycogen (a polymer of glucose) is stored in most tissues.

Glycogen is the storage form of readily available glucose in animals. The glycogen storage disorders (GSD) are metabolic disorders that typically result in tissue accumulation of excessive or abnormally structured glycogen. These often cause liver and muscle disease and may or may not cause neuronal degeneration, hypoglycemia, and/or heart failure. GSD type IV is an autosomal recessive disorder of Norwegian forest cats previously defined in the United States (Fyfe JC et al ., 1992) that causes degeneration of neurons and cardiac and skeletal muscle with death ensuing before a year of age. Hypoglycemia in the immediate postnatal period often causes weakness and death unless treated. The disorder is due to a mutation of the glycogen branching enzyme gene (Fyfe JC et al ., 2007) and storage of abnormally structured glycogen (long outer chains).

Most affected kittens die at birth or soon after birth because they are not able to produce enough glucose during the birth process and the first hours of life. Rarely, affected kittens could live normally until 5 months of age, but the disease leads quickly to neuromuscular degeneration, to severe muscular atrophies, to cardiac failures and to death before 15 months of age.

The GSD IV is inherited as an autosomal recessive trait in the Norwegian Forest Cat. The GSD4 test detects directly the causative mutation in the GBE1 gene. Statistics (frequency of carriers): USA : 15% Europe : 12%

Using this DNA test, breeders are able to detect very early carriers cats, to select breeding animals and to adapt breeding strategies in order to reduce neonatal mortality due to GSD IV, to avoid producing affected kittens, to avoid spreading the genetic defect in their lines or in the breed.

2 normal homozygous cats, so healthy, will only give birth to normal homozygous kittens so healthy. It's useless to consistently test cats if you know that their parents or grand-parents are normal homozygous.

Résultat du test ADN	The cat is	Genetic status	Will develop the disease?	Will transmit the genetic anomaly?
Normal homozygous	Healthy	2 normal copies of GBE1 gene	NO	NO
Heterozygous	Carrier	1 normal copy and 1 defective copy of GBE1 gene	NO	YES statistically to 50% of its progeny
Mutated homozygous	Affected	2 defective copies of GBE1 gene	YES neonatal mortality, potential survival until 15 months	Not able to reproduce

What is the Pyruvate Kinase Deficiency ?

Pyruvate kinase (PK) is an enzyme critical to the anaerobic glycolytic pathway of energy production in the erythrocyte. If PK is deficient in erythrocytes they are unable to sustain normal cell metabolism and hence are destroyed prematurely. This deficiency manifests as an hemolytic anemia of variable severity.

PK deficiency is inherited as an autosomal recessive condition. Carriers with one defective and one normal gene for pyruvate kinase do not have any clinical signs of disease and lead normal lives. However, when used in breeding they are able to propagate mutations throughout the population.

2 normal homozygous cats, so healthy, will only give birth to normal homozygous kittens so healthy. It's useless to consistently test cats if you know that their parents or grand-parents are normal homozygous.

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