Diseases affecting metabolic pathways in the body are classified as storage diseases. There is a build-up of toxic products in the body due to the malfunction of enzymes that normally break down some unwanted products in the body.
What causes storage diseases?
When a pet is diagnosed with a storage disease, it is likely that they inherited it from their parents. A faulty gene causes the disease, and it is common for two copies of the faulty gene to be present (one from each parent). A pet with one faulty gene and one normal gene will usually not be affected, but will be able to pass the disease on to its offspring. In the event that your pet is affected, it is highly likely that they possess two copies of the faulty gene. In some cases, normal siblings may have inherited just one copy of the faulty gene and therefore will not be affected (although they may pass the disease on to their children), while in other cases, they may have inherited two copies of the faulty gene.
Pets cannot recycle waste products if they do not have a copy of the normal gene. As these products accumulate within the cell, they become toxic over time.
What signs occur with a storage disease?
The signs of storage diseases usually appear in young animals (usually between the ages of two months and two years). Occasionally, however, the signs are quite subtle and some animals reach adulthood before they show clinical signs. As a rule, the first problem that is noticed is that the affected animal does not grow as well as its littermates. Signs vary according to the type of disease your pet has, but in many cases there are neurological signs such as tremors, difficulty walking, paralysis, or seizures. The progression of the disease may result in an animal becoming blind or deaf. Because the disease is inherited, often litter mates will also be affected.
How do I diagnose a storage disease?
It is important to run a number of tests when investigating the problem as there are many conditions that can look like storage diseases. As storage diseases are inheritable, it is a good idea to see if the patient is from an at risk breed. The abnormal cells characteristic of this disease can be observed under a microscope by taking tissue samples in some of these conditions. A limited number of diseases can be diagnosed by genetic testing (on a blood sample). There is typically a need for an MRI scan of the brain and/or spine as well as the collection of a sample of brain fluid (cerebrospinal fluid).
Can storage diseases be treated?
Due to the inherent problem in every cell, there is no treatment for this condition. Invariably, the signs will progressively worsen and ultimately prove fatal, and in fact, most affected pets will pass away within 4-6 months. Numerous treatments have been tested on humans, including gene therapy, and, in the future, these may be available for pets as well. Meanwhile, affected pets require high quality nursing care to maintain their quality of life. The life expectancy of affected animals in rare forms of this condition can be as long as three and four years.
How can storage diseases be prevented?
The storage diseases are extremely unpleasant inherited conditions that may have a lethal outcome or result in progressive worsening of clinical signs over time. In the majority of cases, this results in the need to consider euthanasia as a last resort for the affected individual. In order to prevent the condition from being passed on, all possible steps must be taken. The breeding of affected animals should be prohibited in order to avoid the transmission of the disease through the generations. It is possible for unaffected parents to act as ‘carriers’ and produce affected puppies. Identifying suspected carriers of a genetic defect and removing them from breeding programs may be possible where a genetic defect is known. A puppy diagnosed with a storage disease should be discussed with the breeder as soon as possible.