An inherited disorder in which multiple fluid-filled cysts gradually replace the tissue in both kidneys
Polycystic kidney disease is an inherited condition in which the kidneys have a honeycomb appearance as a result of the presence of numerous fluid-filled cysts. The cysts gradually replace normal tissue so that the kidneys become larger and progressively less able to function until eventually they fail completely (see End-stage kidney failure). Polycystic kidney disease is not the same as simple kidney cysts, which are generally harmless.
Polycystic kidneys may affect adults or, rarely, infants. Adult polycystic kidney disease does not usually become apparent until about the age of 45, although symptoms can appear as early as the age of 20. In children, the condition is known as juvenile polycystic kidney disease and is sometimes fatal.
Polycystic kidney disease is caused by an abnormal gene. In the adult form, the gene is inherited in an autosomal dominant manner, and as a result the disease can be inherited from just one parent (see Gene disorders). Each child of such a parent has a 1 in 2 chance of developing the disorder in adulthood. The juvenile form is inherited in an autosomal recessive way; both parents must pass the faulty gene to the child for the disorder to develop. When both parents have one copy each of the faulty gene, each child has a 1 in 4 chance of developing the disorder.
The gene responsible for polycystic kidneys in adults has been identified, and genetic counselling is available for people who have a family history of the disease. If both potential parents are aware that they carry the gene for the juvenile form, they will also need counselling before conceiving. It is possible to check the kidneys of a fetus for signs of the disorder using ultrasound scanning (see Ultrasound scanning in pregnancy). If an ultrasound scan reveals polycystic kidneys in the fetus, the parents can discuss the options available with the doctor.
The symptoms of adult polycystic kidney disease may not appear for many years. The main symptoms are:
Vague discomfort in the abdomen or aching in the lower back.
Episodes of severe and sudden pain in the abdomen or lower back.
Blood in the urine.
A baby with juvenile polycystic disease will have a very swollen abdomen due to enlargement of the kidneys.
In adults, as the disease progresses, high blood pressure (see Hypertension) may develop, which can lead to further kidney damage. Occasionally, one or more of the kidney cysts become infected, resulting in pain and fever. Sometimes, cysts develop in other organs, such as the pancreas and liver.
If you have abdominal pain and notice blood in your urine, you should consult your doctor as soon as possible.
Adult polycystic kidney disease is often first discovered during a routine physical examination. It may also be detected when family members are screened because a relative already has polycystic kidney disease. Blood and urine tests may be performed to assess kidney function, and ultrasound scanning or CT scanning may be carried out to confirm the diagnosis. Healthy children of people with polycystic kidney disease are usually advised to have an ultrasound scan at around the age of 20 to check for the development of the disorder.
If it has not been detected in the fetus, juvenile polycystic kidney disease may be obvious at birth because the baby will have a very swollen abdomen. The diagnosis can be confirmed by ultrasound scanning, which will show enlarged kidneys with cysts.
There is no effective way to prevent the cysts forming, but careful control of high blood pressure may slow the rate of the kidney damage. If the fluid in the cysts is infected, antibiotics may be prescribed. If end-stage kidney failure occurs, dialysis or a kidney transplant will be needed.
The progression of polycystic kidney disease in adults varies considerably. However, the outlook tends to be similar for affected members of the same family. About 7 in 10 of the people who have polycystic kidney disease develop kidney failure by the age of 65.
In a child who has juvenile polycystic kidney disease, the kidneys will fail, and eventually the child will need dialysis or a kidney transplant. Some affected infants may die at only a few months of age due to kidney failure.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.