Storage Diseases of the Nervous System in Dogs

Storage diseases of the nervous system, also known as lysosomal storage diseases or glycogen storage diseases, are a group of rare enzymatic disorders that affect mainly the nervous system. This group of disorders is genetic in nature and is almost always fatal early in life. The best preventative measure for these type of congenital disorders is to identify carriers before they are bred so that the recessive gene is not passed on to their offspring.

A storage disease of the nervous system, or lysosomal storage disease, is a recessive congenital disorder in enzyme production passed down genetically from both parents.

Although lysosomal storage diseases are able to effect any system, most of the symptoms are neurologic in nature. Symptoms will start at different ages depending on which type of storage disease is affecting the dog. Symptoms could include:

• Anxiety
• Behavioral changes
• Daze
• Dementia
• Enlarged liver
• Exercise intolerance
• Failure to thrive
• Fainting
• Hyperactivity
• Loss of coordination
• Muscle weakness
• Seizures
• Stiff gait
• Vision problems 

Types

There are several types of storage diseases of the nervous system that can affect different breeds of dogs, usually at different ages. 

• Ceroid lipofuscinosis - Australian Cattle Dog, Border Collie, Chihuahua, Cocker Spaniel, Dalmatian, English Setter, and Tibetan Terrier show signs of ceroid lipofuscinosis around one to two years old
• Fucosidosis- English Springer Spaniels can show early signs of fucosidosis around six months old and can continue up until four years old
• Glucocerebrosidosis - Australian Silky Terriers show signs of this storage disorder at around four to eight months old
• Glycogen Storage Disease Type III - Akitas and German Shepherds start showing signs of this disorder around six to twelve weeks old and usually succumb by eight months old 
• Gangliosidosis - German Shorthaired Pointers develop a version of gangliosidosis at six to nine months old, however, the Portuguese Water Dog and English Springer Spaniel develop symptoms of this disorder at just two to four months old and succumb by eight months old
• Mucopolysaccharidosis - Plott Hound, Chesapeake Bay Retriever, Welsh Corgi, Rottweiler, and Boston Terrier breeds, as well as miniature Poodles, Pinschers, and Schnauzers,  can be affected by this lysosomal storage disease at around two to five months of age

This disorder is caused by a deficiency in the enzyme production of a particular enzyme that is supposed to break down large molecules within the cells into smaller ones so that they can pass out through the cell membranes. Each variety is deficient in a different enzyme, but they all cause the larger molecules to overcrowd the cell until it is killed.

When you bring your dog into the veterinarian’s office, the examination will start with a physical evaluation. While palpating the dog or puppy’s abdomen, an enlarged liver may be revealed. Standard tests will usually be run including tests such as a biochemical profile, (CBC) complete blood count, and urinalysis. These tests will help to determine the efficiency of the patient's internal organs such as the liver and kidneys, and will also be used to screen for bacterial, fungal, or parasitic infections. 

Test results combined with the breed and age of the young dog may lead the examiner to suspect a storage disorder, which would lead them to order enzyme assay tests to confirm the levels of specific enzymes. Chest x-rays may be ordered to check for tumors or other defects in the esophagus and chest area, and electromyography may be used to evaluate the conductive ability of the motor and sensory pathways.

Unfortunately, there is no cure for these disorders, and they almost always end up being fatal within six months to a year. If your dog or puppy is in a state of crisis when you bring them into the clinic, supportive therapies will be started, including IV fluids to prevent dehydration and adjust for any imbalances in sugar levels. This type of condition is a good candidate for eventual gene therapies.

The primary way to prevent this disorder is through careful testing and selective breeding. In almost all cases this is a recessive trait, meaning that both parents must carry the deficiency in their DNA. Testing is now becoming available for several versions of lysosomal storage disorders so that carriers can be identified ahead of time so that they are not bred.