The word “congenital” means something that is present at the time of birth.
Because of spare renal capacity, a kitten with a congenital kidney disease may lead a normal life for several years and only become sick in later life.
This was the case for a lovely Birman cat I treated named Lola; she was fine until she was 3 years old but then started to drink a lot and lose weight. Lola is slightly unusual because the average age that symptoms break through is at age 5, after the reserve capacity is used up.
Potentially any part of the kidney may not form properly in the womb, and the list of congenital issues is a long one that includes, for example, problems with the blood supply (renal telangiectasia) or the “meaty” part of the kidney (renal dysplasia).
The kidney may be incorrectly plumbed in (ectopic ureter), have a form of early onset cancer (nephroblastoma) or not be able to function correctly (congenital nephrogenic diabetes insipidus).
But of all the congenital kidney diseases, 2 are by far the most common:
- Polycystic kidney disease (PKD)
- Amyloidosis (the condition Lola has)
As a general rule, the kidney is limited in how it shows a problem, and the symptoms are largely the same regardless of the cause.
The signs associated with renal failure include:
- Poor appetite
- Increased thirst (polydipsia)
- Wetting more than usual (polyuria)
- Weight loss
- Lack of energy
- Bad breath
- Stunted growth
In addition, cats with PKD can have swollen bellies because their kidneys are physically much bigger than usual. Also, cats with amyloidosis sometimes develop symptoms such as fluid in the belly or swollen legs and paws.
Congenital disease can come about because of genetic disease, or because the pregnant mother acquired an infection or had contact with a chemical that causes birth defects.
A disturbance in the normal process of assembling the fetal kidney results in the organ being imperfectly made. Because the kidney is designed for a lifetime of use, it has a significant amount of spare capacity; however, with congenital kidney disease, the kitten is born with “short-dated” kidneys that run out of healthy tissue way ahead of schedule.
From the list of possible congenital conditions, the common PKD has arisen as an unhappy result of inbreeding to produce breed characteristics in pedigrees. Thus, PKD is especially common in the Persian and certain exotic shorthair cats; amyloidosis is more common in Abyssinian, Siamese and Oriental shorthair cats.
The diagnostic process starts with analysis of blood and urine samples.
Your veterinarian draws blood to check the levels of naturally occurring toxins of which the kidney should rid itself. However, the “spare” capacity of the kidney means deceptively normal test results until the cat is down to her last 25% of a kidney. It may surprise you, but it is only when 75% of renal function is lost that blood tests show any abnormal reading at all.
However, if the vet is suspicious of juvenile kidney disease but the in-house tests come back normal, a new blood test is available. The SDMA test measures a different natural chemical in the bloodstream, which can highlight problems earlier.
On the other hand, a simple test on urine to see how diluted or concentrated it is and a further test looking at how much protein has leaked into the urine tells a clinician whether this cat has renal problems but is coping — or not.
In breeds such as the Persian, an ultrasound may be performed to examine the texture of the kidney to look for the characteristic cysts associated with PKD. A kidney biopsy gives the definitive diagnosis but is not without risk. It also is not necessary to put an exact name to the condition to treat it since the basis of the treatment is similar in most cases, regardless of cause.
For the majority of congenital kidney diseases there is no cure, and treatment is based on relieving symptoms (such as nausea and poor appetite) and protecting the kidney from further damage.
This includes special diets that produce less toxic metabolites when digested, drugs to maximize the functional capacity of the kidney, phosphate binders (phosphate tends to scar the kidney as it is processed) and antibiotics for any secondary urine infections.
If the cat is doing very poorly and has become dehydrated, then intravenous fluids may be necessary to detox the patient.
Screening and responsible breeding of affected breeds, such as Persians, is vital to avoid breeding from individuals carrying genes for PKD. Unfortunately, there is no substitute for a wide gene pool when trying to reduce the risk of congenital diseases.
- Small Animal Internal Medicine. Nelson & Couto. Publisher: Mosby.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.