Fanconi Syndrome in Dogs

One of the many functions of a normal kidney is the reabsorption of a variety of soluble nutrients out of the urine and back into the bloodstream to be used by various systems in the body. The structures responsible for this process are called the tubules. In dogs with Fanconi syndrome, these tubules do not perform this function properly. Instead of being reabsorbed, the nutrients are flushed out of the body with the urine. This tubular dysfunction leads to electrolyte, acid-base, and protein disturbances along with dehydration and eventually chronic renal failure.

Fanconi syndrome is uncommon in most dog breeds, and is a serious condition. If left untreated, kidney failure occurs and causes death. Immediate veterinary attention is required for dogs with the symptoms of this condition.

The gene that causes hereditary Fanconi syndrome is found in a variety of breeds of dog, but especially in the Basenji. The incidence of Fanconi syndrome in basenjis is estimated at 10-16%.

The acquired form of Fanconi syndrome is possible in all breeds and is more common in dogs with underlying health conditions, who have ingested toxins, or who are on certain medications.

The severity of Fanconi syndrome depends on how many nutrients are being lost, what underlying conditions exist, and whether the syndrome has progressed to kidney failure.

In some cases, only a single nutrient is lost due to Fanconi syndrome. In these cases, especially if it is a less crucial nutrient, the symptoms are milder and the damage to the body less severe. In cases where major nutrients such as glucose, sodium, or bicarbonate are lost, or in cases where many nutrients are lost, the symptoms are more severe and the damage to the body becomes significant.

In addition, dehydration may develop. Symptoms of dehydration include sticky gums, sunken eyes, and delayed skin turgor.

In cases where there is an underlying condition that can be corrected, the symptoms of Fanconi syndrome resolve once the cause is treated. In cases where there is no known underlying cause, where the cause cannot be resolved, or where the cause is genetic, there is no cure for Fanconi syndrome and lifelong management is necessary.

In the most severe cases, Fanconi syndrome progresses to kidney failure.

In some cases, especially in basenjis, Fanconi syndrome is hereditary. The gene for this mutation is known and genetic testing is available.

In other cases, Fanconi syndrome is acquired. Acquired Fanconi syndrome is sometimes caused by toxicoses.

It is also associated with the use of specific medications, although the mechanism is unknown.

Recent reports link Fanconi syndrome occurring in association with some types of jerky treats, but the causative agent or mechanism is not currently known.

Dogs experiencing excessive thirst and urination require prompt veterinary attention. If more serious symptoms are also present, veterinary attention is more urgently needed. Diagnosis is based on physical examination, as well as comparisons of bloodwork and urinalysis.

Additional diagnostic tools vary based on symptoms that point to varying underlying conditions.

There is no cure for Fanconi syndrome. Treatment is first aimed at resolving underlying conditions where these exist.

Management of Fanconi syndrome requires strict, lifelong compliance with a protocol to replace lost nutrients through supplementation and dietary changes.

Dogs diagnosed with Fanconi syndrome require ongoing blood and urine checks throughout their lives to ensure that the nutrients are being effectively replaced through supplementation and diet.

The prognosis for Fanconi syndrome varies.

In cases of hereditary Fanconi syndrome, the prognosis is poor. Affected dogs eventually develop chronic renal failure and die. With strict lifelong adherence to management protocols, it is possible to achieve a good prognosis.

In cases of acquired Fanconi syndrome, the prognosis varies depending on the associated condition. Some underlying conditions are fatal. In cases where the underlying condition can be identified and treated, prognosis is fair to good so long as appropriate supportive care is provided to avoid the development of chronic renal failure.

In both hereditary and acquired Fanconi syndrome, the prognosis is poor to grave in cases that develop chronic renal failure.

Hereditary Fanconi syndrome is preventable by genetic testing and selective breeding.

Strategies for the prevention of acquired Fanconi syndrome include:

• Keeping the dog in excellent health with regular veterinary attention
• Vaccinating at-risk dogs for leptospirosis
• Keeping dogs on veterinary-approved parasite control
• Discretionary and judicious use of antibiotics and other medications
• Avoiding heavy metals and other toxic substances
• Use only veterinarian-approved treats

Fanconi syndrome is uncommon in dogs.

Ongoing supplementation