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According to the American Kidney Foundation, Polycystic Kidney Disease (PKD) is the most common life threatening, genetic disorder caused by a single gene and affects between 1 in 400 and 1 in 1000 people worldwide. Fluid-filled cysts form in the nephrons of both kidneys (bilateral) that eventually lead to kidney failure in the majority of patients. Polycystic kidney disease is the fourth most common cause of kidney failure.

Cysts usually begin as an outpouching (like a blister) anywhere along the nephron. Approximately 70% of the cysts detach from the nephron when they are small and proceed to enlarge as they fill with either clear fluid or fluid that may contain blood cells. Hundreds to thousands of cysts can develop that range from the size of a pinhead to as large as a grapefruit (10-20 cm.) in diameter. Each kidney may expand to as large as a football and may weigh up to 38 pounds.

There are at least three factors related to cyst formation in the kidney but exactly what triggers the process is unclear.

• Increased production of cells of the cyst wall. These cells continue to reproduce all through life enable the cyst to enlarge.
• Increased production of fluid by the cells forming the cyst.
• Abnormal basement membrane (a thin layer of tissue upon which the cyst rests) structure and function. In PKD the makeup of the basement membrane is not normal, the layer is also thicker than normal, and attachment to the cyst wall is increased.

Kidney function is usually eventually compromised to the point that it leads to kidney failure resulting in a loss of its ability to cleanse the blood and concentrate urine. It is thought that the continual enlargement of cysts crowds out healthy kidney tissue. In addition, normal tissue can be actively destroyed (apoptosis) and fibrous tissue can be formed resulting in a condition called interstitial fibrosis. The combination of cysts and progressive interstitial fibrosis is thought to accelerate chronic renal failure. Kidney failure does not usually occur until after the 4th decade.

Hypertension (high blood pressure) is closely associated with polycystic kidney disease due the increased burden placed on the blood vessels resulting from inadequately filtered blood. It is often one of the earliest symptoms of PKD.