Fanconi Syndrome in Dogs

By Krista Williams, BSc, DVM, CCRP; Robin Downing, DVM, DAAPM, DACVSMR, CVPP, CRPP

What is Fanconi Syndrome?

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 abnormal function of a part of the kidneys called the tubules. The tubules should reabsorb water, electrolytes and nutrients that would otherwise be excreted in the urine, but that are critical to normal metabolic function. In dogs with Fanconi syndrome, the tubules do not properly reabsorb  electrolytes and nutrients, instead allowing them to ‘spill’ them back into the urine to be expelled. The electrolytes and nutrients that are excreted in excess in Fanconi syndrome include:

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

Fanconi syndrome has been reported in several different dog breeds, but the vast majority of reported cases (75%) have occurred in Basenjis. Approximately 10 – 30% of Basenjis in North America are affected. Unfortunately, the precise mode of inheritance is not yet known.

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

What are the clinical signs of Fanconi syndrome? 

The signs of Fanconi syndrome vary depending upon 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. Uncommonly, very young dogs can develop Fanconi syndrome, and these dogs have abnormal bone development.

How is Fanconi syndrome diagnosed?

While there are no specific tests for Fanconi syndrome, diagnosis depends upon several factors. Basenjis who drink and urinate more than normal create a high index of suspicion. If there is glucose in the urine, but the level of glucose in the blood is normal, this is highly suspicious of Fanconi syndrome. In fact, this glucose disconnect is often the very first suggestion of Fanconi syndrome, preceding other laboratory markers. Additionally, approximately 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 depends upon the severity of the reabsorption defects and must be individualized to the specific patient. 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 measure specific 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.

Many dogs with Fanconi syndrome do live close to a normal life expectancy. Your veterinarian will guide you as to when (or whether) it is appropriate to begin screening your dog for evidence of Fanconi syndrome.

What is Fanconi-like Syndrome?

This condition has similar symptoms to Fanconi syndrome. It can be caused by the ingestion of certain chicken jerky treats. Once these treats are no longer fed to affected dogs, the clinical signs resolve.

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