Storage diseases in your cat

Storage diseases are a group of inherited diseases affecting metabolic pathways in the body. In these diseases the enzymes that normally break down some unwanted products in the body are not working properly and there is a build up of the products which can be toxic to the cells.

©Simon Platt

Signs of storage diseases usually develop in young animals (usually between 2 months and 2 years of age), but occasionally the signs are quite subtle and some animals reach adulthood before clinical signs are recognized. Often the first problem noticed is that the affected animal does not grow as well as its litter mates. The signs will vary according to which particular form of the disease your pet has; but in many cases there are neurological signs such as tremors, difficulty walking, paralysis or seizures. Some animals become blind or deaf as the disease progresses. Often litter mates will also be affected, because the disease is inherited.

Storage diseases are rare and so it is unlikely to be the first thing your veterinarian suspects as a cause of your pet’s signs. However, when your veterinarian is investigating what is wrong with your pet they will want to do a number of tests and the results from these may make them suspicious of the underlying cause. Since storage diseases are inherited they are typically found in particular breeds of cats so if your kitten is from one of the affected breeds your veterinarian may be more suspicious of the condition. Tissue samples can be taken and examination of these under a microscope may reveal the abnormal cells typical of the disease. For a small number of diseases genetic testing (on a blood sample) is available to confirm the diagnosis.

Unfortunately, there is no treatment for this condition as there is an inherent problem in every cell. Signs will invariably get progressively worse and will ultimately prove fatal, and indeed most affected kittens will die within 4-6 months. In people a number of treatments such as gene therapy have been trialed and, in the future, these may be available for cats. In the meantime affected pets need high quality nursing care to maintain their quality of life for as long as possible. In some of these diseases affected animals may live for 3 to 4 years.

If your pet has been diagnosed with a storage disease then they will have inherited this from their parents. The disease is caused by a faulty gene, and most often two copies of this gene are needed for disease to be present (one from each parent). If an animal has one faulty gene and one normal gene they will usually not be affected, but can pass the disease on to their offspring. If your kitten is affected it most likely means they have two copies of the faulty gene. Normal brother and sisters may have inherited only one copy of the faulty gene and therefore will not be affected (but could pass the disease on to their offspring) or they may have inherited two normal copies of the gene.

Without a copy of the normal gene, the cells in your pet’s body are unable to make the enzymes needed for recycling the waste products they produce. With time these products accumulate within the cell and become toxic.

Storage diseases are very unpleasant inherited conditions that may be lethal, or may result in progressive worsening of clinical signs over time. This most often results in a need to consider euthanasia for affected individuals with time. It is important to take all possible steps to avoid passing on the condition. Affected animals should not be allowed to breed as they can pass the condition on through the generations. However, it is possible for unaffected parents to act as ‘carriers’ and produce affected kittens. Where genetic defect is known, testing may be available to identify suspected carriers and remove them from breeding programs. If your kitten is diagnosed with a storage disease it is very important to talk to the breeder of your pet and let them know about the condition.