Fanconi syndrome

What is ... ?: 

In the normal kidney, there is selective reabsorption of water, sugars, minerals, and amino acids so that these substances are not lost excessively in the urine. In a dog affected with Fanconi syndrome, there is a defect in the tubules of the kidney where this resorption occurs. Loss of these substances (that would normally be conserved) leads to various serious problems for the animal such as electrolyte imbalances, dehydration and weight loss.
 
This disease can also be acquired in any breed (as opposed to inherited) as a result of various toxins (e.g., heavy metals).

How is ... inherited?: 

This is a significant disorder in the Basenji breed, affecting upwards of 10% of dogs. The mode of inheritance is presumed to be autosomal recessive. This disorder has also been seen in other breeds (as below) - mode of inheritance unknown.

What does ... mean to your dog & you?: 

Dogs that are affected with this disorder usually show signs anywhere from 3 to 7 years of age. The earliest signs are excessive drinking and urination, because the kidneys are unable to conserve water. Because of the loss of nutrients and electrolytes in the urine, your dog may experience weight loss and muscle weakness. The condition may worsen slowly over several years, or may progress rapidly to kidney failure with signs such as poor appetite, extreme loss of weight, lethargy, vomiting, and pale gums due to anemia. Dogs with Fanconi syndrome are prone to urinary tract infections due to the sugar in the urine.

How is ... diagnosed?: 

The signs described above can have several causes. Your veterinarian will do blood and urine tests that will point to your dog's kidneys as the cause of the problem.
 
FOR THE VETERINARIAN
Laboratory findings include low urine specific gravity, glucosuria with normoglycemia (diagnostic in a Basenji), phosphaturia, and aminoaciduria. The defective urine concentrating ability represents a form of nephrogenic diabetes insipidus; isosthenuria or hyposthenuria may precede glucosuria. There may be mild proteinuria.
 
As the disease progresses, dogs will develop azotemia, hypophosphatemia, variable metabolic acidosis (hyperchloremic), and hypokalemia (which may contribute to the muscle weakness sometimes seen). Unlike other hereditary kidney diseases, the primary abnormality is functional with little apparent structural change. The kidneys are generally grossly normal, and lesions with light microscopy are variable and non-specific.
 
Primary renal glucosuria is an uncommon disorder in which there is glucosuria with normal blood glucose concentrations and otherwise normal kidney function. It can be differentiated from Fanconi syndrome based on the absence of other solutes (amino acids, electrolytes) in the urine. It has been found in the Norwegian elkhound and may cause urinary tract infections.

How is ... treated?: 

There is no cure, but there are ways to slow the progression of kidney disease, which your veterinarian will discuss with you. These include making sure your dog always has access to fresh drinking water and, depending on the stage of the disease, feeding a special (high quality, low-protein) diet and the use of some medications which help to support kidney function. Regular monitoring of kidney function is important.

For the veterinarian: Management of this disease includes regular monitoring; vitamin, mineral and amino acid replacement; control of metabolic acidosis with sodium bicarbonate; and medical management of uremia of chronic renal failure as necessary. Potassium citrate therapy provides both alkalinization and potassium supplementation.

Breeding advice: 

Fanconi syndrome is an important problem in the Basenji breed, affecting 10% or more of dogs. Affected dogs should not be bred and, because the mode of inheritance is unconfirmed, it is safest to avoid breeding either parent or any siblings. One problem for breeders is that the condition may not become evident until 6 or 7 years of age. There is a linked marker DNA test available for Basenjis through the OFA that gives results of probable normal, probable carrier, probable affected, and indecisive.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources: 

Langston C. Fanconi syndrome. In: Côté E, ed. Clinical Veterinary Advisor Dogs and Cats. Missouri: Mosby Elsevier, 2007:375-376.
 
Sargan DR. Fanconi syndrome. In IDID - Inherited diseases in dogs:web-based information for canine inherited disease genetics. 2002-2011.
 
Basenji Health Issues information


What breeds are affected by ... ?
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