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Polycystic kidney disease (PKD) is characterized by the growth of numerous cysts in the kidneys. The Polycystic Kidney Disease Foundation (PKDF) estimates over half a million people in the United States suffer with PKD. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) calls it the fourth leading cause of kidney failure. (Read about kidney failure in "Kidney Disease")
The cysts, which are filled with fluid, can slowly replace much of the mass of the kidneys, reducing kidney function and leading to kidney failure. When PKD causes kidneys to fail - which usually happens only after many years, according to NIDDK - the patient requires dialysis or kidney transplantation. (Read about "Transplants") PDKF says that over half of people with the major type of PKD progress to end-stage renal disease or ESRD. (Read about "End Stage Renal Disease")
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. They are part of the urinary system and filter wastes from the blood to form urine. They also regulate amounts of certain vital substances in the body. (Read about "Kidney Disease")
PKD can cause cysts in the liver and problems in other organs, such as the heart and blood vessels in the brain. (Read about "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, according to NIDDK.
NIDDK says there are three major inherited forms of PKD and a noninherited form:
Below find information on these three forms of PKD.
Autosomal dominant PKD is one of the most common inherited disorders. PKDF estimates one in four hundred to one in a thousand adults have this condition. The phrase "autosomal dominant" means that if one parent has the disease, there is a 50-percent chance that the disease will pass to a child. At least one parent must have the disease for a child to inherit it. Either the mother or father can pass it along, but new mutations may account for one-fourth of new cases. NIDDK says that in some rare cases, the cause of autosomal dominant PKD occurs spontaneously in the child soon after conception - in these cases the parents are not the source of this disease.
Many people with autosomal dominant PKD live for decades without developing symptoms. For this reason, autosomal dominant PKD is often called "adult polycystic kidney disease." Yet, in some cases, cysts may form earlier, even in the first years of life.
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 African Americans (Read about "Minority Health") and more often in females than in males. High blood pressure (Read about "Hypertension: 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, according to NIDDK.
The most common symptoms are pain in the back and the sides (between the ribs and hips), and headaches. The dull pain can be temporary or persistent, mild or severe.
People with autosomal dominant PKD also can experience the following, according to NIDDK:
NIDDK says to diagnose autosomal dominant PKD; a doctor typically observes three or more kidney cysts using ultrasound imaging. (Read about "Ultrasound Imaging") The diagnosis is strengthened by a family history (Read about "Family Health History") of autosomal dominant PKD and the presence of cysts in other organs.
An ultrasound imaging device passes harmless sound waves through the body to detect possible kidney cysts.
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 check-ups 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.
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, according to NIDDK. (Read about "CT Scan - Computerized Tomography" "MRI - Magnetic Resonance Imaging") CT scans require x-rays and sometimes injected dyes.
A genetic test has recently been developed and is commercially available to detect mutations in the PKD1 and PKD2 genes, according to NIDDK. This test can detect the presence of the autosomal dominant PKD mutations before cysts develop, but its usefulness is limited by the fact that the test cannot predict ultimate severity or onset of disease, and by the fact that no absolute cure is available to prevent the onset of the disease. A young person who knows of a PKD gene mutation may be able to forestall the disease through diet and blood pressure control. The test may also be used to determine whether a young member of a PKD family can safely donate a kidney to a parent. NIDDK says anyone considering genetic testing should receive counseling to understand all the implications of the test.
Although a cure for autosomal dominant PKD is not available, treatment can ease the symptoms and prolong life, according to NIDDK.
NIDDK says autosomal recessive PKD is caused by a particular genetic flaw that is different from the genetic flaw that causes autosomal dominant PKD. Parents who do not have the disease can have a child with the disease if both parents carry the abnormal gene and both pass the gene to their baby. The chance of this happening (when both parents carry the abnormal gene) is one in four. If only one parent carries the abnormal gene, the baby cannot get the disease.
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.
Children with autosomal recessive PKD experience high blood pressure, urinary tract infections (Read about "Urinary Tract Infections") and frequent urination, according to NIDDK. The disease usually affects the liver, spleen (Read about "The Spleen"), and pancreas, resulting in low blood-cell counts, varicose veins (Read about "Varicose Veins"), and hemorrhoids (Read about "Hemorrhoids"). Because kidney function is crucial for early physical development, children with autosomal recessive PKD are usually smaller than average size.
Ultrasound imaging (Read about "Ultrasound Imaging") of the fetus or newborn baby reveals cysts in the kidneys but does not distinguish between the cysts of autosomal recessive and autosomal dominant PKD. Ultrasound examination of kidneys of relatives can be helpful; for example, a parent or grandparent with autosomal dominant PKD cysts could help confirm diagnosis of autosomal dominant PKD in a fetus or child. (It is extremely rare, although not impossible, for a person with autosomal recessive PKD to become a parent.) Because autosomal recessive PKD tends to scar the liver, ultrasound imaging of the liver also aids in diagnosis.
Medicines can control high blood pressure in autosomal recessive PKD, and antibiotics can control urinary tract infections. Eating increased amounts of nutritious food improves growth in children with autosomal recessive PKD. In some cases, growth hormones are used. (Read about "Growth Hormone") In response to kidney failure, autosomal recessive PKD patients must receive dialysis or transplantation
ACKD develops in kidneys with long-term damage and bad scarring, so it often is associated with dialysis and end-stage renal disease, according to NIDDK. About 90 percent of people on dialysis for 5 years develop ACKD. People with ACKD can have any underlying kidney disease, such as glomerulonephritis or kidney disease of diabetes. (Read about "Diabetes and Kidney Disease")
The cysts of ACKD may bleed. Kidney tumors, including kidney (renal) cancer (Read about "Kidney 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, says NIDDK.
Patients with ACKD usually seek help because they notice blood in their urine (hematuria). The cysts bleed into the urinary system, which discolors urine. (Read about "The Urinary System") Diagnosis is confirmed using ultrasound, CT scan or MRI of the kidneys. (Read about "Ultrasound Imaging" "CT Scan - Computerized Tomography" "MRI - Magnetic Resonance Imaging")
Most ACKD patients are already receiving treatment for kidney problems. In rare cases, surgery is used to stop bleeding of cysts and to remove tumors or suspected tumors.
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