Genetic Diseases PKD and HCM

Polycystic Kidney Disease (PKD)

Cornell Feline Health Center
Cornell University College of Veterinary Medicine
Ithaca, New York 14853

Occurring most frequently in Persian cats, polycystic kidney disease is an inherited disorder in which small, closed, liquid-filled sacs develop in the tissue of the feline kidney. These sacs (cysts) tend to multiply in number and grow in size over time, eventually overwhelming normal kidney tissue and often leading to potentially fatal kidney failure. There is no explanation for the development of these cysts except for a genetic anomaly that is evident primarily in Persians and occasionally in a few other feline breeds, such as Himalayans and British Shorthairs.

“You can have one large cyst or 30 or more small cysts,” says Richard Goldstein, DVM, associate professor of small animal medicine at Cornell University’s College of Veterinary Medicine. “In an advanced stage of the condition, it’s possible for the sacs to become so large and numerous that you can actually see the kidney’s outline when an affected cat is lying on its back. When you examine the animal, the kidney will seem to be unusually large, but you may not be able to actually feel the stones because they’re on the interior wall of the organ.” Eventually, however, the cysts may become so large that their bulging distends the kidney’s surface and can be felt during the course of a veterinary examination.

In an affected cat, the cysts are present at birth and, though minuscule, may be diagnosed in kittens as young as six months of age. The number of these cysts varies from cat to cat, as does their size and the rate at which they grow within the kidney. The growths in a mature cat typically range in size from less than one millimeter to more than a centimeter in diameter. Clinical signs of polycystic kidney disease are most often recognized in cats that are seven years of age or so, although the disorder may be diagnosed in patients that are several years younger or older than that.

The clinical signs of this condition are typically the same as those associated with kidney disease in general, says Dr. Goldstein: increased drinking and urination; diminished appetite and weight loss; nausea and vomiting; and lethargy. “It’s not like there’s a cluster of grapes inside the kidney,” he points out, “so you usually can’t feel the cysts by themselves. And you can’t see them on a radiograph. You can run a genetic test, but that won’t tell you how seriously the cat is affected. So the only way to get a definitive diagnosis is by using ultrasound.”

It is conceivable, according to Dr. Goldstein, that cysts within the kidney could be drained with a needle in a procedure guided by ultrasound imaging. “But there usually are so many cysts,” he notes, “that this is not a viable option. And even if you did drain all of them, they would fill up with fluid again.”  So the only feasible approach to managing the condition, he  points out, is the same as that recommended for addressing kidney failure in general—a combination of diet control, fluid therapy, and certain medications that are prescribed by a veterinarian. “The goal is to keep the kidneys as happy as we can for as long as we can,” says Dr. Goldstein.

Considering the dreadful implications of polycystic kidney disease, owners should take advantage of the only method known to prevent its occurrence. That is, any cat considered to be a possible carrier of the gene responsible for the disorder—especially a Persian cat—must undergo a test to determine whether or not it is indeed harboring the responsible gene. If it turns out that the cat is in fact carrying the gene, it must not be allowed to breed.

By Tom Ewing
February 12, 2011

 

Cardiomyopathy (HCM)

Cornell Feline Health Center
Cornell University College of Veterinary Medicine
Ithaca, New York 14853

The feline heart, like the human heart, is a hollow, muscular organ located in the center of the chest. Both the right and left sides of the organ have an upper chamber (atrium), which collects circulating blood, and a lower chamber (ventricle), which pumps blood from the heart.

Cardiomyopathy, which literally means “disease of the heart muscle,” is brought about by a structural abnormality in the tissue enclosing one or more of these chambers. In general, says Marc Kraus, DVM, a senior lecturer in cardiology at Cornell University’s College of Veterinary Medicine, the heart muscle either grows too thick to function properly or it stretches and becomes too thin. In either case, the abnormality sets the organ’s blood-collecting and blood-pumping mechanics awry, a dysfunction that often leads to congestive heart failure with respiratory distress, paralysis-causing blood clots, and, in some cases, sudden death.

Most feline cardiomyopathies are primary diseases—those whose origins are either genetic or unknown. Some, however, are secondary diseases—those whose causes are specifically identifiable, such as hyperthyroidism or high blood pressure.

Three types of the disorder account for nearly all cardiomyopathies. The most common type by far is hypertrophic cardiomyopathy. Developing with no feasible explanation other than the strong likelihood of hereditary influence, this condition—which occurs most often in male cats—is characterized by a thickening of the muscle tissue associated with the left ventricle. This thickening results in poor heart function and, sometimes, obstruction of blood flow from the heart. It also causes the upper heart chambers to become enlarged. The consequence of these combined factors is a condition in which the heart fails to relax fully and fills with circulating blood. This can result in increased fluid pressure in the lungs and shortness of breath. In addition, blood clots may develop in the left atrium. If a clot breaks up, small pieces of it may circulate and eventually lodge in an artery leading to the legs. This may cause the sudden onset of lameness or paralysis, often accompanied by severe pain.

The second most common type, Dr. Kraus points out, is restrictive cardiomyopathy. This condition is caused by the excessive buildup of scar tissue on the inner lining and muscle of the ventricle, which prevents the organ from relaxing completely, filling adequately, and emptying with each heartbeat.

The third type—dilated cardiomyopathy—is relatively rare, says Dr. Kraus. The condition is chiefly characterized by a poorly contracting dilated left ventricle. The heart walls are thin and flaccid, which results in a decreased forward flow of blood from the heart and, consequently, heart failure. The condition is rare these days, notes Dr. Kraus, due to the fact that cat food manufacturers have, for the past three decades or so, been routinely adding an important amino acid called taurine to their products. Prior to that, a lack of taurine in cat food had been closely linked to the incidence of dilated cardiomyopathy.

Male and female cats of any age—even kittens—are susceptible to one form or another of cardiomyopathy, says Dr. Kraus, although most patients are middle-aged males. And among all feline breeds, he adds, Maine Coons and Ragdolls seem to be at elevated risk.
The most common clinical signs include rapid breathing, lethargy, and diminished appetite. If the condition progresses and the heart’s blood-collecting and blood-pumping mechanisms continue to fail, congestive heart failure ensues, which can lead to severe respiratory distress, paralysis-causing blood clots, and eventual death. Owners should know that a cat that is struggling to take in air or has trouble moving its rear legs may be experiencing advanced cardiomyopathy and must receive veterinary help immediately.

The initial objective in diagnosing cardiomyopathy is to exclude other heart conditions that could have similar signs. In most cases, radiographs will be taken. Sometimes an electrocardiogram will be required. The definitive diagnosis, however, will be obtained via an echocardiogram (an ultrasound of the heart), which Dr. Kraus refers to as “the gold standard” for diagnosing this condition. Treatment with certain medications may be initiated. For example, beta-blockers may help the heart muscle relax by slowing the patient’s heart rate, thereby decreasing its need for oxygen. With appropriate care, a cat diagnosed with cardiomyopathy may survive for several years. “But once heart failure occurs,” says Dr. Kraus, “a cat may be able to stay alive for up to a year or so. But some will succumb before that.”

By Tom Ewing
August 30, 2010