Polycystic kidney disease
Polycystic kidney disease
Description, Causes and Risk Factors:
Alternative Names: Autosomal dominant polycystic kidney disease (ADPKD).
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 and extra fluid from the blood to form urine. They also regulate amounts of certain vital substances in the body. Polycystic kidney disease (PKD) is a genetic disorder characterized by the growth of numerous cysts in the kidneys.
Polycystic kidney disease is a kidney disorder passed down through families in which multiple cysts form on the kidneys, causing them to become enlarged. PKD is passed down through families (inherited), usually as an autosomal dominant trait. If one parent carries the gene, the children have a 50% chance of developing the disorder.
Autosomal dominant PKD occurs in both children and adults, but it is much more common in adults, with symptoms often not showing up until middle age. It affects nearly 1 in 1,000 Americans. The actual number may be more, as some people do not have symptoms. The disorder may not be discovered unless tests revealing the disease are performed for other reasons.
An autosomal recessive form of polycystic kidney disease also exists and appears in infancy or childhood. This type tends to be very serious and progresses rapidly, resulting in end-stage kidney failure and generally causing death in infancy or childhood.
Persons with PKD have multiple clusters of cysts form on the kidneys. The exact action that triggers cyst formation is unknown. In early stages of the disease, the cysts cause the kidney to swell, disrupting kidney function and leading to chronic high blood pressure and kidney infections. The cysts may cause the kidneys to increase production of erythropoietin, a hormone that stimulates production of red blood cells. This leads to too many red blood cells, rather than the anemia seen in chronic kidney disease.
Autosomal dominant PKD is the most common inherited form. Symptoms usually develop between the ages of 30 and 40, but they can begin earlier, even in childhood. About 90 percent of all PKD cases are autosomal dominant PKD.
Autosomal recessive PKD is a rare inherited form. Symptoms of autosomal recessive PKD begin in the earliest months of life, even in the womb.
Scientists have located two genes associated with autosomal dominant PKD. The first was located in 1985 on chromosome 16 and labeled PKD1. PKD2 was localized to chromosome 4 in 1993. Within 3 years, scientists had isolated the proteins these two genes produce—polycystin-1 and polycystin-2.
When both the PKD1 and PKD2 genes are normal, the proteins they produce work together to foster normal kidney development and inhibit cyst formation. A mutation in either of the genes can lead to cyst formation, but evidence suggests that disease development also requires other factors, in addition to the mutation in one of the PKD genes.
Genetic analyses of most families with PKD confirm mutations in either the PKD1 or PKD2 gene. In about 10 to 15 percent of cases, however, families with autosomal dominant PKD do not show obvious abnormalities or mutations in the PKD1 and PKD2 genes, using current testing methods.
Researchers have also recently identified the autosomal recessive PKD gene, called PKHD1, on chromosome 6. Genetic testing for autosomal recessive PKD to detect mutations in PKHD1 is now offered by a limited number of molecular genetic diagnostics laboratories in the United States.
Abdominal pain or tenderness.
Blood in the urine.
Excessive urination at night.
Flank pain on one or both sides.
Additional symptoms that may be associated with this disease include the following:
High blood pressure.
PKD is often diagnosed when a person begins to have the symptoms listed above, but not all people who have PKD will have all of these symptoms. If you have symptoms of PKD or if you are at risk for the disease, your doctor may want you to have an ultrasound exam. An ultrasound exam uses sound waves to create a picture of your organs and can detect cysts on the kidneys. Your doctor may also order a CT (computerized tomography) scan to look for cysts in the kidney.
Polycystic kidney disease and associated cysts on the liver or other organs may be detected with the following tests:
Abdominal CT scan.
Abdominal MRI scan.
In a family with several members with PKD, genetic tests can be done to determine whether a person at risk carries the PKD gene. Gene linkage analysis involves special blood tests for you and for at least three family members who are known either to have or not to have polycystic kidney disease. Then, the results of your blood tests are compared with the results of the tests of your family members. Because ultrasound and other imaging tests generally result in a definitive diagnosis, this test is often only used when a young family member is considering donating a kidney. It may also be used when results of the imaging tests aren't conclusive.
PKD can be diagnosed in unborn babies using a test called amniocentesis. During this test, a very small amount of the amniotic fluid is taken out of the womb. The fluid is then tested. Another test, called chorionic villus sampling, involves testing a very small piece of the placenta.
No treatment is available for the cysts caused by PKD. If the cysts are causing symptoms, these symptoms can be treated so you will be more comfortable. The goal of treatment is to control symptoms and prevent complications. High blood pressure may be difficult to control, but control of it is the most important aspect of treatment.
Treatment may include:
Rarely, when kidney cysts are causing severe pain or obstructing other organs or blood vessels, you may need to undergo surgery to drain the cysts.
If your kidneys lose their ability to remove wastes and extra fluids from your blood, you'll eventually need either dialysis or a kidney transplant.
Blood pressure medicines.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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