Fanconi syndrome is a form of proximal renal tubular acidosis characterized by a lack of reabsorption of certain solutes from the urine. Glucose and bicarbonate are the most commonly affected solutes, but also potentially affected are amino acids, small molecular weight proteins, phosphate, potassium, calcium, sodium, magnesium, uric acid, and organic acids . The congenital form of Fanconi syndrome in Basenjis is best characterized; however, other breeds can also have the congenital form, and acquired forms can affect any breed.
Acquired causes include certain antibiotics (ie, gentamicin, cephalosporins, tetracyclines, high doses of amoxicillin, salicylates), heavy metal toxicities (eg, lead, copper, mercury), other toxicants (eg, melamine, organomercurials, Lysol, maleic acid), other medications (eg, cisplatin, streptozotocin), neoplasia, monoclonal gammopathies, amyloidosis, hypovitaminosis D, copper hepatopathy, and hypoparathyroidism.2,3,5
Dogs with congenital or acquired Fanconi syndrome can have normal lifespans with proper treatment; prognosis is dependent on identification of underlying cause(s) and development of renal failure. If untreated, any form of Fanconi syndrome can progress to kidney disease and life-threatening acidosis.
Owners may not notice signs at home. The most common sign, polyuria and polydipsia, is secondary to glucosuria, causing osmotic diuresis. Other reported signs at home are vague (eg, weight loss, poor hair coat, dehydration, muscle weakness). The physical examination is frequently normal other than a presenting thin body condition. CBC and serum biochemistry profile may be normal or demonstrate azotemia, hypophosphatemia (which differentiates this from typical chronic kidney disease, in which the phosphorous is usually increased), hyperchloremia (to compensate for the loss of bicarbonate), and hypokalemia. The serum glucose, calcium, and total protein levels are usually normal. A urinalysis will reveal glucosuria (although normoglycemia differentiates this from diabetes), low urine specific gravity, alkalotic urine (although if the distal renal tubules are still functioning, the urine pH may be normal or acidic), and varying degrees of proteinuria or albuminuria.
A venous blood gas should be performed to better characterize the patient acid-base status; arterial blood gases do not yield additional information and is technically more demanding. A normal anion gap metabolic acidosis with low bicarbonate is typically identified. Paired urine and serum samples should be evaluated to measure amino acids and determine the degree of aminoaciduria. In some patients, only some or even only single amino acids are affected.
Once Fanconi syndrome has been diagnosed, treatment is warranted, including removing the underlying cause (if possible) and treating with aggressive bicarbonate supplementation. The Gonto protocol, involving aggressive bicarbonate supplementation, is one treatment modality; others include diet changes and vitamin and mineral supplementation. This is reportedly effective in Basenjis. Supplementation of potassium and other electrolytes (if low) is warranted, as is maintenance of good hydration status.
There have been recent reports of a Fanconi syndrome-like condition associated with ingestion of chicken jerky treats.1 FDA investigations are ongoing without established causality or identification of the toxic ingredient. Although most dogs reported have had transient illness, at least one has died from progressive kidney disease secondary to the Fanconi-like syndrome. A thorough diet and medication history should be obtained in any dog with suspected Fanconi-like syndrome, and a report should be submitted to the FDA. Every attempt should be made to differentiate this disease from other conditions, including diabetes mellitus, chronic kidney disease, and urinary tract infections. The hallmark finding of glucosuria with normoglycemia should raise the clinical index of suspicion; blood work and urinalysis abnormalities should be confirmed with a reputable laboratory.
Editor's note: This article was originally published in November 2012 as "Fanconi Syndrome: A Review"