Did you know that dogs can get many of the same diseases as people? Osteoarthritis, diabetes mellitus and congestive heart failure are a few of the most common. But there are rarer conditions that both humans and dogs can have too, such as today’s topic: Fanconi syndrome. A complex disease of the kidneys, today we will discuss what Fanconi syndrome is, how it affects dogs, and how vets diagnose and treat it.
Physiology of the Kidneys
To understand Fanconi syndrome, it is first important to understand how the kidneys work. The physiology is similar between dogs and people, so this applies to both species.
The kidneys
The kidneys are organs located in the upper part of the abdomen, one left and one right. Their primary roles are the removal of waste products from the body and controlling water concentration in the blood. They are also involved in the secretion of certain hormones, helping control the acidity of blood, maintaining blood pressure, and resorbing important substances like glucose and electrolytes. To fulfil these functions, the kidneys filter the body’s blood multiple times a day through tiny tubes called nephrons. Each kidney has thousands of nephrons. To reach the kidneys, blood flows from the heart into a large vessel called the aorta. Near the kidneys, branches called the renal arteries divert to the kidneys. The arteries then branch into tiny blood vessels that enter the kidneys, before leaving again to empty into the renal veins and finally the vena cava and back to the heart.
Within the kidneys, the blood vessels are under high pressure, which forces water, electrolytes and other components out of blood and into the nephrons, specifically the glomerulus. The rate this takes place is called the Glomerular Filtration Rate (GFR). The GFR can be altered by various factors. This step is called ultrafiltration.
Next, the fluid travels through a system of tubes
These are the proximal convoluted tubules, the Loop of Henle, and the distal convoluted tubules. These tubes are surrounded by blood vessels – fluid and electrolytes can move back and forth between the tubes and the blood vessels. Through a very complex mechanism of pressures and concentrations, important electrolytes like glucose and amino acids are fully absorbed back into blood, and water and sodium are absorbed. This step is selective resorption and water conservation.
Finally, in the collecting ducts, after some further minor adjustments, the fluid is now considered urine containing excess electrolytes and waste products. The urine leaves the kidneys via the ureters, which flow into the bladder to be stored. It is finally excreted when urination takes place.
What is Fanconi Syndrome?
Fanconi syndrome is a condition where the proximal convoluted tubules that usually resorb glucose, amino acids, sodium, potassium and other electrolytes are not working properly. This results in these important electrolytes being leaked into urine, causing a deficiency in the blood. In advanced cases, damage to the kidneys can progress to kidney failure.
The condition can be a genetic disorder, most commonly in Basenji dogs, though it has been reported in other breeds as well. These dogs can show symptoms as early as 11 weeks old, but mostly present from 4-7 years old.
However, rarely it can also be acquired due to damage to the proximal convoluted tubules. This can occur after the misuse of certain antibiotics, toxicity from heavy metals like lead or copper, certain cancers, and metabolic diseases including hypoparathyroidism and hypovitaminosis D. Interestingly, over the last few years a number of cases of Fanconi syndrome have been linked to dried meat products imported from China. Thankfully, a review of 30 cases of ‘jerky-induced Fanconi syndrome’ (JFS) found that 24 resolved completely after stopping feeding the treats. Eleven did require veterinary treatment, however, including 7 requiring hospitalisation. Care should still be taken when feeding dogs certain treats, but bear in mind that the exact ingredient causing JFS has not yet been identified.
What Are the Symptoms?
The symptoms of Fanconi syndrome are all associated with electrolyte loss and kidney disease. The most common reported symptoms are excessive drinking and excessive urination. Many dogs are lethargic, have weight loss and a reduced appetite. Some will have vomiting and diarrhoea. Advanced renal failure can progress to dehydration, collapse and eventually death. Others can develop chronic renal disease.
Dogs that develop symptoms very young may not grow properly and can have muscle and bone disorders. Seizures have also sometimes been reported, but it is not clear if this is directly related to Fanconi syndrome. The aforementioned study did note that two of the 30 dogs did not have any symptoms from JFS.
How is Fanconi Syndrome Diagnosed?
Diagnosing Fanconi syndrome requires several steps. History and clinical examination can often point towards a kidney problem, but this requires blood and urine analysis to confirm.
Dogs with Fanconi syndrome will usually have increased blood creatinine and urea (waste-products the kidneys usually remove from the blood), but reduced potassium and phosphate (due to loss into urine). There can be metabolic acidosis too due to loss of bicarbonate. Some dogs may have normal blood values however. Glucose is usually normal, which can help differentiate the condition from diabetes mellitus. Other non-specific findings may include damage to the liver; and blood, protein or ketones in the urine.
Urine usually reveals high glucose (due to loss into the urine), low urine concentration, and increased alkalinity. Amino acids can be detected in the urine using specialised tests.
A genetic test is available for Basenjis that identifies the abnormal gene, but does not necessarily determine if the dog will go on to develop Fanconi syndrome or not.
How Can it be Treated?
If Fanconi syndrome is acquired, particularly due to jerky-treats, removing the underlying cause should be the first approach. In some cases, as the study found, this was enough to completely reverse the disease. Other treatments include supplementing bicarbonate, potassium and other electrolytes if they are deficient, to make up for renal losses. Encouraging drinking to reduce dehydration is also important. One protocol, the ‘Gonto protocol’ has been developed (though not peer reviewed) for Basenjis that claims to have a good outcome.
If dogs have concurrent renal disease they often require hospitalisation with intra-venous fluid therapy to support the kidneys and reduce dehydration. Other care may include anti-emetics, pain relief and antibiotics for secondary infection.
What is the Prognosis for Fanconi Syndrome?
The prognosis can vary for Fanconi syndrome and depends on the cause, when the disease is identified and if there is already kidney disease. The author of the Gonto protocol claims that Basenjis treated with their method can give normal lifespan and quality of life, whereas without many will die within 18 months of symptoms starting. These cases are likely those that develop rapid kidney failure. A study of 60 dogs with inherited Fanconi syndrome (58 Basenjis) found that the median lifespan for these dogs was 11.3-12.1 years, quite close to the natural lifespan of these dogs. Even with the disease, 97% of dogs were reported by their owners to have a good or better condition. The study in 30 dogs found almost all dogs with JFS had a complete reversal of symptoms, though two developed chronic kidney disease.
Therefore, in summary, it can be determined that the outcome for Fanconi syndrome is good provided the condition is diagnosed early and managed well.
Further reading
Update on Fanconi Syndrome and Cystinuria – Veterinary Information Network
Fanconi Syndrome – Renal Tubular Defects in Dogs and Cats – MSD Vet Manual
Fanconi Syndrome Review – Clinician’s Brief
Survival time, lifespan, and quality of life in dogs with idiopathic Fanconi syndrome – JAVMA
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