Glycogen storage disease in cats

Written by Liz Palika Reviewed by Kristin Westafer, DVM

Overview

Glycogen is sugar that is stored in the liver for future use. Glycogen Storage Diseases (GSD) are inherited metabolic disorders that disrupts that body's ability to store or use glycogen. Cats with GSD have a deficiency or absence of an enzyme necessary to make or break down glycogen.

There are several forms of GSD and each causes a different problem within a different area in the body. Enzymes are necessary to break down glycogen; without them, glycogen accumulates in abnormal quantities in cells of the body and prevents them from functioning normally. There is a form of GSD that interferes with normal glycogen synthesis. While this form does not cause a large accumulation of glycogen in the tissues of the body, it is in fact an abnormal process and can cause similar problems. Therefore with GSD, there might be too much or too little glycogen in the muscles, the heart, or the red blood cells.

GSD IV is a form typically seen most commonly in Norwegian Forest Cats. Mucolipidosis Type II is a form most commonly seen in domestic shorthaired cats.

Symptoms

Most cats with GSD are normal at birth. Symptoms develop before 6 months of age and continue to worsen over 1 to 2 years. Kittens may also be stillborn or die shortly after birth. Symptoms of affected cats include:

Fever
Muscle tremors
Muscle jerks
Progressive weakness
Muscle atrophy
Contracted muscles
Difficulty swallowing
Skeletal malformations

Cause and treatment

GSD has been found in people, cattle, sheep, dogs, cats, and several other animal species. In all cases it appears to be strictly inherited with the highest occurrences appearing when both the mother and father are carriers of the gene which produces GSD.

John Fyfe, DVM, PhD, has studied GSD in conjunction with the Norwegian Forest Cat Fanciers Association in North America. Norwegian Forest Cats can carry this disease and in some lines, as many as 25% of all kittens are either stillborn or die shortly after birth. Dr. Fyfe says, at this time, nothing can be done to treat the affected kittens. The disease process appears to be inevitable and lethal.

Responsible breeders must identify those cats who are carriers so the continuation of this horrible disease can be halted. All breeding animals should be tested to see if they are carriers prior to using them for breeding, especially if GSD are suspected in the breeding line.

Most pet owners will never see this disease as most kittens with it will pass away before birth, at birth, or are humanely euthanized shortly after diagnosis. Owners of affected cats should be aware that their cats may become increasingly aggressive as this disease progresses and care should be taken when small children are in the household.

This is a serious disease with no cure; treatment is aimed at lessening clinical symptoms. If your cat has been diagnosed with a GSD, consultation with a veterinary neurologist is recommended for the most up to date treatment options.