Gangliosidosis (storage disease)
Storage diseases are those in which a cell’s genetically inherited inability to manufacture a particular enzyme means that the body ends up “storing” too much of whatever product the enzyme would normally help deal with. The upshot is a backing up of critical processes that leads to the swelling of affected cells and a wide variety of pathological outcomes, usually with devastating consequences for the long-term survival of the individual. The nervous system is most commonly affected.
In humans, these diseases are rare but they’ve been very well studied as they affect children and because the gene therapy may be on the horizon. Consequently, dogs have both served this body of research and benefited from it immensely.
In dogs, storage diseases are also considered rare. They deserve attention, however, not only because so many of them have been well studied but because very specific breeds suffer from them. Where it has been established, the inheritance has been determined to be autosomal recessive in nature.
Gangliosidosis is only one of little more than a score of these well-studied canine storage diseases. Two varieties are known to exist. Both affect the nervous system in similar ways.
Symptoms and Identification
Gangliosidosis patients tend to be normal very early on in life. When compared to their littermates, however, their growth soon appears stunted and within the first few months of life they’ll develop symptoms consistent with a neurologic disease. Though vision and coordination are first and foremost affected, progressive lethargy and difficulty ambulating, in general, is to be expected.
While both forms of gangliosidosis lead to similar, eventually fatal symptoms (usually within six months of its appearance), the two forms differ in their onset and in the breeds they affect. For GM1 gangliosidosis, pups first show signs at 2 to 4 months. For GM2 gangliosidosis, six to nine months is more the norm. Refer to the following section for details on affected breeds.
Diagnosis for all storage diseases is almost always achieved by measuring the levels of the deficient enzyme. In both forms of gangliosidosis, enzyme levels confirm the suspicion raised by clinical signs, age and breed.
GM1 gangliosidosis: Portuguese Water Dog and English Springer Spaniel
GM2 gangliosidosis: German Shorthair Pointer
Sadly, there is thus far no known treatment for any of the storage diseases. Gene therapy, however, is highly anticipated in humans with similar storage diseases. The fact that one discrete gene is typically responsible for each of these diseases means that these are likely to be most amenable to gene therapy, once our medical technology makes it available.
Unfortunately, euthanasia is the upshot in almost all these cases. Diagnosis, however, may prove pricey as tests for specific enzymes or carrier states, because so infrequently undertaken (rare as these diseases are), will almost certainly mean a higher expense than for more standard blood tests.
Ideally, prevention requires an aggressive response within the breeding program to terminate the affected line unless specific testing is undertaken to identify asymptomatic carriers of the disease. Such tests are available for gangliosidosis. Only an assiduously implemented breeding program devoid of all potential carriers will effectively eliminate the inheritance of this disease.
Ackerman, L. 1999. The Genetic Condition: A Guide to Health Problems in Purebred Dogs. pp 103-107. AAHA Press. Lakewood, Colorado.
March, P.A. 1996. Degenerative brain disease. Vet. Clin. of N.A. Small Animal Practice. 26(4): 945-971.
Canine Inherited Disorders Database