Polycystic kidney disease
Polycystic kidney disease (PKD) is a genetic disorder characterized by the development of numerous fluid-filled cysts in the kidneys, which can significantly impair kidney function and potentially lead to renal failure. It affects approximately 600,000 people in the United States and is a leading cause of kidney failure globally. There are two primary forms of PKD: autosomal dominant PKD, which typically manifests in adulthood, and autosomal recessive PKD, which primarily affects children. Symptoms of autosomal dominant PKD may include high blood pressure, back and side pain, and complications like urinary tract infections and brain aneurysms.
As the cysts grow, they can lead to kidney enlargement, with advanced cases resulting in kidneys weighing as much as 22 pounds. Unfortunately, PKD cannot be cured, and treatment focuses on alleviating symptoms and preventing complications through medications, lifestyle changes, and potentially dialysis or kidney transplantation. Research into the genetic basis of PKD has advanced significantly, with scientists exploring potential therapies that could further improve treatment outcomes. Despite its challenges, ongoing studies aim to enhance understanding and management of this complex condition.
Polycystic kidney disease
ANATOMY OR SYSTEM AFFECTED: Blood vessels, brain, gastrointestinal system, kidneys, liver, pancreas
DEFINITION: A genetic disorder characterized by multiple, bilateral, grape-like clusters of fluid-filled cysts that slowly replace much of the mass of the kidney, reducing kidney function and leading to renal failure
CAUSES: Genetic defect; long-term kidney damage associated with dialysis, end-stage renal disease
SYMPTOMS: Cysts in kidneys, kidney enlargement, high blood pressure; may include pain in back and side, headaches, blood in urine, urinary tract infections, brain aneurysms, cysts in liver and pancreas, nail abnormalities, painful menstruation, varicose veins, hemorrhoids, joint pain, drowsiness, anemia
DURATION: Progressive, usually fatal without treatment
TREATMENTS: Alleviation of symptoms and prevention of complications; may include analgesics (aspirin, acetaminophen), antibiotics, iron supplements, blood transfusions, cyst drainage, dialysis, kidney transplantation
Causes and Symptoms
About 600,000 people in the United States have polycystic kidney disease (PKD), and 12.5 million suffer from it worldwide; it is the fourth leading cause of kidney failure. There are two major inherited forms of PKD, autosomal dominant and autosomal recessive, and a noninherited form called acquired cystic kidney disease (ACKD). The autosomal dominant type is the most common inherited form.
Autosomal dominant PKD has a slow onset, with symptoms usually developing between the ages of thirty and forty. Sometimes, symptoms do not appear until age seventy. Cysts grow out of the nephrons, the blood-processing units in the kidneys. High blood pressure occurs, and the kidney enlarges as the cysts form. A normal kidney weighs 10 to 12 ounces and is the size of a human fist. A cyst-filled kidney can weigh as much as 22 pounds and can grow to the size of a football or larger. Healthy kidney tissue is destroyed as the cysts produce pressure on it, and renal failure eventually occurs. Once uremic symptoms appear, the disease is usually fatal within four years unless the patient receives dialysis or a kidney transplant. This destruction of kidney tissue may take as long as ten years.
Several other symptoms are associated with autosomal dominant PKD. Patients experience pain in the back and side, as well as headaches. Blood may appear in the urine, and urinary tract infections occur. Aneurysms in the blood vessels of the brain can also appear. Cysts may form in the liver and pancreas, and even the heart valves may be affected. Life-threatening bleeding into the abdominal cavity from cyst ruptures can occur. Other symptoms often associated with the disease are nail abnormalities, painful menstruation, joint pain, drowsiness, and anemia.
Autosomal dominant PKD is thought to occur equally in men and woman and in all races; however, some studies suggest that it occurs more often in White females than in African Americans. Diagnosis can be made by ultrasound, computed tomography (CT) scanning, and magnetic resonance imaging (MRI). Genetic tests are run to identify the presence of the autosomal dominant gene.
Autosomal recessive PKD usually affects children. Patients experience high blood pressure, urinary tract infections, and frequent urination. The liver, spleen, and pancreas are usually affected, resulting in low blood cell counts, varicose veins, and hemorrhoids. The child is usually smaller in size than average.
Autosomal recessive PKD can be diagnosed by ultrasound imaging of the fetus or newborn, which will reveal cysts in the kidneys. However, this procedure does not distinguish between the cysts of autosomal recessive and autosomal dominant PKD. Performing ultrasound examinations of relatives can be helpful in making a diagnosis.
The noninherited type of cystic disease is ACKD. It develops in kidneys as a result of long-term damage and bad scarring and is associated with dialysis and end-stage renal disease (ESRD). About 90 percent of people who have been on dialysis for five years or more develop ACKD. People with ACKD may have underlying conditions such as glomerulonephritis or kidney disease associated with diabetes mellitus. The cysts of ACKD may bleed, and patients may develop renal cancer.
Treatment and Therapy
Polycystic kidney disease cannot be cured. The goals of treatment are the reduction of symptoms and the prevention of complications. Analgesics such as aspirin or acetaminophen (Tylenol) are used to treat the pain. If severe headaches occur, however, then an aneurysm may be involved. Therefore, the patient should see a physician before using over-the-counter medications.
Antibiotics are given to treat urinary tract infections, and high blood pressure is treated with proper diet, exercise, and medications as prescribed by a physician. Any symptoms of anemia are treated with iron supplements or blood transfusions.
Surgical drainage of cysts may be indicated because of pain, bleeding, infection, or obstruction. Because of the large number of cysts, surgery to remove them is not deemed proper. Eventually, the kidney may fail as a result of tissue destruction by the cysts, and dialysis and kidney transplantation become the only methods of treatment.
Perspective and Prospects
The first recorded case of polycystic kidney disease dates back to Stefan Bathory, the king of Poland who lived from 1533 to 1588. In the mid-1980s, the Polycystic Kidney Disease Foundation was formed.
Through extensive genetic research, a better understanding of PKD has been gained. In 1985, the first gene associated with autosomal dominant PKD was located on chromosome 16; in 1993, another was located on chromosome 4. Within three years, scientists isolated the proteins produced by these two genes, polycystin 1 and polycystin 2. Since then, scientists have identified the autosomal recessive PKD gene on chromosome 6.
Researchers are using mice bred with this genetic disease in an attempt to find a cure. In 2000, they reported that a cancer drug was successful in inhibiting cyst formation in mice with the PKD gene. The hope is that further testing will lead to safe and effective treatments for humans.
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