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Fanconi Syndrome in Dogs

Fanconi syndrome is a collection of abnormalities arising from the defective transport of water, sodium, potassium, glucose, phosphate, bicarbonate, and amino acids from the kidneys; impaired tubular reabsorption, the process by which solutes and water are removed from the tubular fluid and transported into the blood, causes excessive urinary excretion of these solutes.

Approximately 75 percent of the reported cases have occurred in the Basenji breed; estimates of the prevalence within the Basenji breed in North America range from 10–30 percent. It is presumed to be an inherited trait in this breed, but the mode of inheritance is unknown.

Idiopathic (unknown cause) Fanconi syndrome has been reported sporadically in several different breeds, including border terriers, Norwegian elkhounds, whippets, Yorkshire terriers, Labrador retrievers, Shetland sheepdogs, and mixed-breed dogs. Age at diagnosis ranges from 10 weeks to 11 years, with most affected dogs developing clinical signs from about two to four years. There is no gender predilection.

Symptoms and Types

Symptoms vary depending on the severity of specific solute losses, and whether renal failure has developed.

• Excessive urination (polyuria)
• Excessive thirst (polydipsia)
• Reduced appetite
• Weight loss
• Lethargy
• Poor body condition
• Reduced and/or abnormal growth (rickets) in young, growing animals

Causes

• Inherited in most cases, particularly in Basenjis
• Acquired Fanconi syndrome has been reported in dogs treated with gentamicin (antibiotic), streptozotocin (chemical used to treat cancer), and amoxicillin (antibiotic)
• Also reported secondary to primary hypoparathyroidism (underactive parathyroid glands)

Diagnosis

Your veterinarian will conduct a complete blood profile, including a chemical blood profile, a complete blood count, and a urinalysis to test levels of sodium, potassium, glucose, phosphate, bicarbonate, and amino acids. An analysis of blood gases will also probably be used to determine whether the kidneys are functioning normally with regards to absorption. You will need to give a thorough history of your pet's health, and onset of symptoms.

Prevention

Avoid drugs that are nephrotoxic (toxic to the kidney), or have the potential to cause Fanconi syndrome (see causes).

Treatment

Discontinue any drug that may cause acquired Fanconi syndrome, or treat for a specific intoxication. There is no treatment to reverse the transport defects in dogs with inherited or idiopathic disease. Because the number and severity of transport defects vary markedly between animals, treatments for potassium deficiency, too much acid in the kidney, renal failure, or rickets must be individualized. Young, growing dogs may require vitamin D and/or calcium and phosphorus supplementation.

Living and Management

Your veterinarian will want to monitor your dog's serum biochemistry at 10 to 14-day intervals to assess the effect of treatment and any change in parameters. Because bicarbonate therapy may aggravate renal potassium loss, your doctor will want to monitor serum potassium concentration regularly; once stable, serum chemistry can be checked at two to four month intervals. The course of the disease varies. Some dogs will remain stable for years, while others will develop rapidly progressive renal failure over a few months. When this disease is fatal, the cause of death is usually acute renal failure, often associated with severe metabolic acidosis. Some dogs (18 percent in one study) develop seizures or other neurologic dysfunction (clumsiness, dementia, or central blindness) several years after diagnosis. The cause of these symptoms is unknown.