The kidneys are two organs, each about the size of a fist, located in the upper part of a person's abdomen, toward the back. The kidneys filter wastes from the blood to form urine. They also regulate amounts of certain vital substances in the body.
When PKD causes kidneys to fail-which usually happens only after many years-the patient requires dialysis or kidney transplantation. About one-half of people with the major type of PKD progress to kidney failure, i.e., end-stage renal disease (ESRD).
PKD can cause cysts in the liver and problems in other organs, such as the heart and blood vessels in the brain. These complications help doctors distinguish PKD from the usually harmless "simple" cysts that often form in the kidneys in later years of life.
In the United States, about 500,000 people have PKD, and it is the fourth leading cause of kidney failure. Medical professionals describe two major inherited forms of PKD and a noninherited form:
The disease is thought to occur equally in men and women and equally in people of all races. However, some studies suggest that it occurs more often in whites than in blacks and more often in females than in males. High blood pressure occurs early in the disease, often before cysts appear.The cysts grow out of nephrons, the tiny filtering units inside the kidneys. The cysts eventually separate from the nephrons and continue to enlarge. The kidneys enlarge along with the cysts (which can number in the thousands), while retaining roughly their kidney shape. In fully developed PKD, a cyst-filled kidney can weigh as much as 22 pounds.
People with autosomal dominant PKD also can experience the following:
In most cases of autosomal dominant PKD, the person's physical condition appears normal for many years, even decades, so the disease can go unnoticed. Physical checkups and blood and urine tests may not lead to diagnosis. The slow, undetected progression is why some people live for many years without knowing they have autosomal dominant PKD.
Once cysts have formed, however, diagnosis is possible with imaging technology. Ultrasound, which passes sound waves through the body to create a picture of the kidneys, is used most often. Ultrasound imaging employs no injected dyes or radiation and is safe for all patients including pregnant women. It can also detect cysts in the kidneys of a fetus.
More powerful and expensive imaging methods such as computed tomography (CT scan) and magnetic resonance imaging (MRI) also can detect cysts, but these methods usually are not required because ultrasound provides adequate information. CT scans require x-rays and sometimes injected dyes.
In the future, DNA testing will be able to confirm a diagnosis of autosomal dominant PKD before cysts develop. (See The Search for PKD Genes)
Pain. A doctor will first suggest over-the-counter pain medications, such as aspirin or Tylenol. For most but not all cases of severe pain, surgery to shrink cysts can relieve pain in the back and flanks. However, surgery provides only temporary relief and does not slow the disease's progression, in many cases, toward kidney failure.
Headaches that are severe or that seem to feel different from other headaches might be caused by aneurysms, or swollen blood vessels, in the brain. Headaches also can be caused by high blood pressure. People with autosomal dominant PKD should see a doctor if they have severe or recurring headaches-even before considering over-the-counter pain medications.
Urinary Tract Infections. Patients with autosomal dominant PKD tend to have frequent urinary tract infections, which can be treated with antibiotics. People with the disease should seek treatment for urinary tract infections immediately, because infection can spread from the urinary tract to the cysts in the kidneys. Cyst infections are difficult to treat because many antibiotics do not penetrate into the cysts. However, some antibiotics are effective.
High Blood Pressure. Keeping blood pressure under control can slow the effects of autosomal dominant PKD. Lifestyle changes and various medications can lower high blood pressure. Patients should ask their doctors about such treatments. Sometimes proper diet and exercise are enough to keep blood pressure low.
End-Stage Renal Disease. Because kidneys are essential for life, people with ESRD must seek one of two options for replacing kidney functions: dialysis or transplantation. In hemodialysis, blood is circulated into an external machine, where it is cleaned before reentering the body; in peritoneal dialysis, a fluid is introduced into the abdomen, where it absorbs wastes, and it is then removed. Transplantation of healthy kidneys into ESRD patients has become a common and successful procedure. Healthy (non-PKD) kidneys transplanted into PKD patients do not develop cysts.
The symptoms of autosomal recessive PKD can begin before birth, so it is often called "infantile PKD." Children born with autosomal recessive PKD usually develop kidney failure within a few years. Severity of the disease varies. Babies with the worst cases die hours or days after birth. Children with an infantile version may have sufficient renal function for normal activities for a few years. People with the juvenile version may live into their teens and twenties and usually will have liver problems as well.
The cysts of ACKD may bleed. Kidney tumors, including kidney (renal) cancer, can develop in people with ACKD. Renal cancer is rare yet occurs at least twice as often in ACKD patients as in the general population.
In 1985, scientists narrowed their hunt for a PKD gene to a particular portion of human chromosome 16. In 1994, they precisely identified a gene associated with the vast majority of cases of autosomal dominant PKD. They named the gene "PKD1," knowing that one or more additional genes for autosomal dominant PKD have yet to be found. By 1995, scientists had produced a map of the PKD1 gene, showing all of its molecular components.
Scientists have continued to search for the autosomal recessive PKD gene. By 1995, they knew that a gene responsible for at least some cases of autosomal recessive PKD resides on chromosome 6.
Scientists will study PKD genes to learn their effects on chemical processes in the body. Knowing the effects will lead to better treatments for the diseases. Eventually, scientists may be able to correct genetic defects, eliminating the diseases entirely.
A genetic disease occurs when one or both parents pass abnormal genes to a child at conception. If receiving an abnormal gene from just one parent is enough to produce a disease in the child, the disease is said to have dominant inheritance. If receiving abnormal genes from both parents is needed to produce disease in the child, the disease is said to be recessive.
The chance of acquiring a dominant disease (one gene copy is enough) is higher than the chance of acquiring a recessive disease (two gene copies are needed). A child who receives only one gene copy for a recessive disease at conception will not develop the genetic disease (such as autosomal recessive PKD), but could pass the gene to the following generation.
American Association of Kidney Patients
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Tampa, FL 33602
National Kidney Foundation
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New York, NY 10016
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The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases, one of the National Institutes of Health, under the U.S. Public Health Service. The clearinghouse, authorized by Congress in 1987, provides information about diseases of the kidneys and urologic system to people with such afflictions and their families, health care professionals, and the public. NKUDIC answers inquiries; develops, reviews, and distributes publications; and works closely with professional and patient organizations and government agencies to coordinate resources about kidney and urologic diseases.
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