What is Difference between PKD different and simple kidney cysts?

It is normal for our kidneys to develop small, fluid-filled cysts as we age. These are called simple kidney cysts and are almost always benign (not harmful). In contrast, PKD occurs when a genetic disease causes cysts to form and grow out of control and overrun the kidneys. These cysts can slowly damage the kidneys and, in some cases, cause the kidneys to fail.