Cysts are noncancerous (benign) sacs that contain water-like fluid. They vary in size and as they accumulate more fluid can grow extremely large. Normally, a kidney weighs less than one-third of a pound (approximately three-quarters of a kilogram), while a kidney containing numerous cysts can weigh as much as 20 to 30 pounds (9.1 to 13.6 kilograms).

Abnormal genes cause polycystic kidney disease, and the genetic defects mean the disease runs in families. Rarely, a genetic mutation can be the cause of polycystic kidney disease. There are two types of polycystic kidney disease, caused by different genetic flaws:

  • Autosomal dominant polycystic kidney disease (ADPKD). Signs and symptoms of ADPKD often develop between the ages of 30 and 40. In the past, this type was called adult polycystic kidney disease, but children can develop the disorder. Only one parent needs to have the disease in order for it to pass along to the children. If one parent has ADPKD, each child has a 50 percent chance of getting the disease. This form accounts for about 90 percent of cases of polycystic kidney disease.
  • Autosomal recessive polycystic kidney disease (ARPKD). This type is far less common than is ADPKD. The signs and symptoms often appear shortly after birth. Sometimes, symptoms don't appear until later in childhood or during adolescence. Both parents must have abnormal genes to pass on this form of the disease. If both parents carry a gene for this disorder, each child has a 25 percent chance of getting the disease.

Researchers have identified two genes associated with ADPKD and one associated with ARPKD.

In some cases, a person with ADPKD has no known family history of the disease. However, it's possible that someone in the affected person's family actually did have the disease, but didn't show signs or symptoms before dying of other causes. In a smaller percentage of cases where no family history is present, ADPKD results from a spontaneous gene mutation.

Nov. 18, 2011