Fanconi Syndrome in Dogs

What is Fanconi syndrome?

Fanconi syndrome affects the kidneys. The kidneys perform many critical functions in the body: they regulate fluid balance, filter toxins from the blood, excrete waste products, and balance the concentration of many different compounds. Fanconi syndrome refers to the abnormal function of a part of the kidneys called the tubules, which normally reabsorb water, electrolytes, and nutrients that are critical to normal metabolic function.

In dogs with Fanconi syndrome, the tubules do not properly reabsorb electrolytes and nutrients; instead, they allow them to spill back into the urine and be expelled. The electrolytes and nutrients excreted in excess include the following:

• Sodium
• Potassium
• Glucose (sugar)
• Phosphate
• Bicarbonate
• Amino acids

Inherited Fanconi syndrome has been reported in several dog breeds, but the vast majority of reported cases have occurred in basenjis. Approximately 10% – 16% of basenjis in North America are affected. In this breed, the condition is inherited as an autosomal recessive disease. This condition has also been associated with the Irish wolfhound, miniature schnauzer, Norwegian elkhound, and Shetland sheepdog. 

Affected individuals may exhibit signs of Fanconi syndrome as early as 11 weeks of age, but typically, clinical signs emerge from 4 to 7 years of age. Ultimately, kidney failure develops in these dogs. Males and females are equally affected. 

Acquired (not inherited) Fanconi syndrome can occur secondary to certain infections (like leptospirosis), low parathyroid hormone levels, and toxin ingestion.

What are the clinical signs of Fanconi syndrome?

The signs of Fanconi syndrome vary depending on the severity of nutrient loss and whether kidney failure has developed. Excessive drinking and urinating are the most common clinical signs. Dogs with Fanconi syndrome may lose weight, despite eating normally. As the disease progresses, affected dogs develop poor body condition and may experience decreased appetite and lethargy. Rarely, very young dogs can develop Fanconi syndrome, and these dogs have abnormal bone development.

How is Fanconi syndrome diagnosed?

There are no specific tests for Fanconi syndrome, and diagnosis depends on several factors. Basenjis who drink and urinate more than normal raise suspicions. Fanconi syndrome is also suspected if there is glucose in the urine but normal levels of glucose in the blood. In fact, this glucose disconnect is often the first suggestion of Fanconi syndrome, preceding other laboratory markers. Additionally, about 1/3 of cases develop low blood potassium levels.

How is Fanconi syndrome treated?

There is no way to reverse the abnormal reabsorption of solutes that occurs in Fanconi syndrome. Management of this disease must be individualized to the patient and depends on the severity of the reabsorption defects. Treatment may include potassium supplementation, nutritional management of kidney disease, and support of normal acid-base balance in the body.

What is the expected outcome for dogs with Fanconi syndrome?

The clinical course of Fanconi syndrome varies, so it is important to perform blood tests every couple of weeks initially to assess the effects of treatments. Once the values are stable, these tests will be rechecked every two to four months.

Some dogs remain stable for years, but others may develop rapidly progressing kidney failure over just a few months. Most dogs with Fanconi syndrome ultimately die of end-stage kidney failure. The variability among Fanconi patients emphasizes the need for regular, ongoing monitoring of metabolic function via laboratory tests.

In dogs with acquired Fanconi syndrome, prognosis depends on the underlying cause (e.g., infection). Many dogs with Fanconi syndrome have close to a normal life expectancy. Your veterinarian will discuss when (or whether) it is appropriate to begin screening your dog for evidence of Fanconi syndrome.