About two-thirds of cases are caused by an enlargement of the adrenal glands, while the majority of the remainder are caused by a tumor on the adrenals. More rarely, it is caused by adrenal cancer or by a genetic condition. About 10% of patients with high blood pressure also have Conn's. It is more common in women, and usually is first diagnosed in patients over 30 but under 50. In addition, about 40% of patients have been identified with a common gene even in non-genetic cases.