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Polycystic kidney disease (PKD) is a genetic disorder characterized by the growth
of
numerous cysts in the kidneys. The cysts are filled with fluid. PKD cysts can slowly
replace
much of the mass of the kidneys, reducing kidney function and leading to kidney failure.
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:
Autosomal dominant PKDis 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.
Acquired cystic kidney disease (ACKD) develops in association with
long-term kidney problems, especially in patients who have kidney failure and who
have been on dialysis for a long time. Therefore it tends to occur in later years
of life.
It is not an inherited form of PKD.
Autosomal dominant PKD is one of the most common inherited disorders. 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 (see Genetic Diseases). 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. 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 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.
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:
Urinary tract infections
Hematuria (blood in the urine)
Liver and pancreatic cysts
Abnormal heart valves
High blood pressure
Kidney stones
Aneurysms (bulges in the walls of blood vessels) in the brain
Diverticulosis (small sacs on the colon).
To diagnose autosomal dominant PKD, a doctor typically observes three or more kidney
cysts using ultrasound imaging. The diagnosis is strengthened by a family 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 systs.
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)
Although a cure for autosomal dominant PKD is not available, treatment can ease the
symptoms and prolong life.
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.
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, and frequent urination. The disease usually affects the liver, spleen,
and pancreas,
resulting in low blood-cell counts, varicose veins, and hemorrhoids. Because kidney
function
is crucial for early physical development, children with autosomal recessive PKD
are usually
smaller than average size.
Ultrasound imaging of the fetus or newborn baby reveals cysts in the kidneys but
does not
distinguish between the cysts of auto-somal 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.
In
response to kidney failure, autosomal recessive PKD patients must receive dialysis
or
transplantation. (See End-Stage Renal Disease)
Genetic Diseases
Genes are segments of DNA, the long molecules that reside in the nuclei of your body's
cells. The genes, through complex processes, cause chemical activities that lead
to
growth and maintenance of the body. At conception, DNA (and therefore genes) from
both parents are passed to the child.
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.
ACKD develops in kidneys with long-term damage and bad scarring, so it often is associated
with dialysis and end-stage renal disease. 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.
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.
Patients with ACKD usually seek help because they notice blood in their urine (hematuria).
The cysts bleed into the urinary system, which discolors urine. Diagnosis is confirmed
using
ultrasound, CT scan, or MRI of the kidneys.
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.
Scientists have not determined the processes that trigger formation of PKD cysts.
However,
in recent years progress has been made in understanding the abnormal genes responsible
for
autosomal dominant and autosomal recessive PKD. Scientists have not yet developed
clinical
tests that determine whether a person carries a PKD gene.
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.
The three types of PKD are:
Two inherited forms:
A common form usually causes symptoms in midlife.
A rare form usually causes symptoms in early childhood.
A noninherited form is associated with long-term kidney problems, dialysis, and
old age.
The signs of PKD include:
Pain in the back and lower sides
Headaches
Urinary tract infections
Blood in the urine
Cysts in the kidneys and other organs.
Diagnosis of PKD is obtained by:
Ultrasound imaging of kidney cysts
Ultrasound imaging of cysts in other organs
Family medical history.
PKD has no cure. Treatments include:
Medicine and surgery to reduce pain
Antibiotics to resolve infections
Dialysis and transplantation to replace functions of failed kidneys.
Polycystic Kidney Research Foundation
4901 Main Street
Suite 320
Kansas City, MO 64112
(800) 753-2873
American Association of Kidney Patients
100 South Ashley Drive
Suite 280
Tampa, FL 33602
(800) 749-2257
National Kidney Foundation
30 East 33rd Street
New York, NY 10016
(800) 622-9010
The U.S. Government does not endorse or favor any specific commercial product or
comany. Trade, proprietary, or company names appearing in this publication are used
only
because they are considered essential in the context of the information reported
herein.
National Kidney and Urologic Diseases Information
Clearinghouse
3 Information Way
Bethesda, MD 20892-3580
E-mail: nkudic@info.niddk.nih.gov
The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) is a
service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
The NIDDK is part of the National Institutes of Health under the U.S. Public Health
Service.
Established in 1987, the clearinghouse provides information about diseases of the
kidneys
and urologic system to people with kidney and urologic disorders and to 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.
Publications produced by the clearinghouse are carefully reviewed for scientific
accuracy,
content, and readability.
This e-text is not copyrighted. The clearinghouse encourages users of this e-pub
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and distribute as many copies as desired.
NIH Publication No. 96-4008
April 1996
e-text posted: 12 February 1998
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