Polycystic kidney disease (PKD or PCKD, also known as polycystic kidney syndrome) is a genetic disorder in which abnormal cysts develop and grow in the kidneys. Cystic disorders can express themselves at any point, infancy, childhood, or adulthood. The disease occurs in humans and some other animals. PKD is characterized by the presence of multiple cysts (hence, "polycystic") typically in both kidneys; however, 17% of cases initially present with observable disease in one kidney, with most cases progressing to bilateral disease in adulthood.