Lysosomal Storage Diseases in Dogs

Metabolic enzyme deficiencies cause specific lysosomal storage diseases, depending upon which enzyme a dog lacks. When the metabolic process does not occur, the metabolic product that should be broken down in order for the body to function accumulates, causing swelling and organ dysfunction. Genetic metabolic enzyme deficiencies manifest soon after birth, when a healthy puppy fails to thrive and does not develop at the same rate as the rest of his litter. Lysosomal storage diseases progress rapidly, and affected dogs typically die between four to six months of age, as there is no cure.

In addition to the common symptoms of failure to thrive and slow development, specific metabolic enzyme deficiencies affect specific aspects of a dog’s functioning.

Ceroid lipofuscinosis
The lack of an enzyme that breaks down lipopigments, which are a fat, leading to their buildup in neuronal cells and organs such as the spleen, liver, and kidneys. It affects Border Collies, Chihuahuas, Cocker Spaniels, Dachshunds, English Setters and Salukis. Specific symptoms include:

• Diminished eyesight
• Behavioral changes
• Dementia
• Seizures
• Ataxia (loss of muscle coordination)

Gangliosidoses
The lack of an enzyme that breaks down gangliocides, a surface molecule in brain cells, which affects Beagle crosses, German Shorthaired Pointers, and Japanese Spaniels. Specific symptoms include:

• Reduced vision
• Lethargy
• Weakness
• Behavioral changes
• Dementia
• Stiff gait
• Incoordination
• Tremors
• Paraparesis (partial paralysis)

Globoid cell leukodystrophy
Also known as Krabbe’s Disease, it is the lack of an enzyme that breaks down psychosine, a galactolipid responsible for the facilitation of nerve impulses. It affects Beagles, Bluetick Hounds, Cairn Terriers, Poodles and West Highland Terriers. Specific symptoms include:

• Impaired vision
• Tremors
• Exaggerated gait
• Incoordination
• Paraparesis (partial paralysis)

Glucocerebrosidosis
The most common metabolic enzyme deficiency, it is caused by a lack of the enzyme that breaks down glucosylceramidase, causing them to accumulate in the brain, liver and lymph nodes. It affects Australian Silky Terriers and Dalmatians. Specific symptoms include:

• Incoordination
• Tremors
• Exaggerated gait
• Hyperactivity

Glycogenosis
A deficiency in the enzyme that breaks down glycogen, a form of glucose stored in the liver and muscles, which affects Australian Silky Terriers. Specific symptoms include:

• Incoordination
• Tremors
• Decreased energy
• Seizures

Mucopolysaccharidosis
A deficiency in the enzymes that break down glycosaminoglycans, which build bone, cartilage, tendons, corneas, skin and connective tissue and affects Miniature Pinschers, Mixed-breed dogs, and Plott Hounds. Specific symptoms include:

• Weakness beginning in hind legs and progressing to all limbs
• Skeletal dysmorphism
• Corneal clouding

Phosphofructokinase deficiency
Also known as glycogen storage disease type VII or Tarui’s disease, a deficiency in the enzyme that enables skeletal muscle cells to break down carbohydrates for energy, it affects Cocker Spaniels and English Springer Spaniels. Specific symptoms include:

• Anxiety
• Incoordination
• Dementia
• Seizures
• Difficulty swallowing
• Altered voice

Pyruvate kinase deficiency
A deficiency in pyruvate kinase leads to an inability to metabolize red blood cells and affects Basenjis, Beagles, Cairn Terriers and West Highland Terriers. Specific symptoms include:

• Anemia
• Weakness
• Muscle wasting
• Jaundice
• Pale mucous membranes
• Elevated heart rate

Sphingomyelinosis
The lack of an enzyme that breaks down sphingomyelin, the phospholipids that create phosphoric acid, sphingosine and fatty acid in nervous tissue, which affects German Shepherds and Poodles. Specific symptoms include:

• Incoordination
• Exaggerated gait
• Dullness
• Tremors

• Genetic
• Lack of enzymes required to perform basic metabolic functions

Proper diagnosis will be assisted by knowing the symptoms for the specific metabolic enzyme deficiency your dog’s breed puts it at risk for. Your veterinarian will be able to determine through physical examination if your dog’s symptoms match a specific disorder and confirm the diagnosis through testing.

A blood sample will be taken in order to be analyzed for a complete blood count, measuring red and white blood cells, as well as a blood chemistry profile, measuring levels of glucose, potassium, nitrogen, calcium and other substances. An additional blood test, known as an enzyme assay, may be used to measure the level of specific enzymes in order to obtain an accurate diagnosis. Abnormalities in the blood chemistry profile will point to problems with specific organ functioning. A urinalysis will be performed in order to assess urinary and kidney functioning. Depending upon the specific deficiency suspected, additional testing may or may not include x-rays and/or ultrasound or tissue biopsy.

Unfortunately, there is no cure for metabolic enzyme deficiencies, and the only treatments are palliative. As this is a fatal condition, you may choose euthanasia or a palliative plan to minimize discomfort. Treatments may include IV fluids in case of dehydration, dietary changes, close monitoring, and restriction of activity. Most dogs will die of the condition by six months of age.

As recovery is not possible with metabolic enzyme deficiencies, afflicted puppies may live out the rest of their lives in managed care. Measures include ensuring access to water to prevent dehydration, following a diet designed to prevent elevated blood sugar, monitoring of the progression of symptoms and preventing the dog from injuring itself by limiting physical activity.

It is important to note that metabolic enzyme deficiencies are autosomal recessive conditions, meaning that two genes for the condition must be present in order for the offspring to inherit it. It is for this reason that inbreeding increases the prevalence of these disorders in purebred populations, and precautions should be taken to eliminate inbreeding.