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Polycystic Kidney Disease
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 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.
- 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
What Is Autosomal Dominant 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. 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.
What Are the Symptoms of Autosomal Dominant PKD?
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).
How Is Autosomal Dominant PKD Diagnosed?
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.
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.
How Is Autosomal Dominant PKD Treated?
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
What Is Autosomal Recessive PKD?
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.
What Are the Symptoms of Autosomal Recessive PKD?
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.
How Is Autosomal Recessive PKD Diagnosed?
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.
How Is Autosomal Recessive PKD Treated?
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.
Acquired Cystic Kidney Disease
What Is ACKD?
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.
How Is ACKD Diagnosed?
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.
How Is ACKD Treated?
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.
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.
Points to Remember
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.
Source:
NIH Publication No. 96-4008
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