A rare, genetic disorder that affects the endocrine glands and causes a type of thyroid cancer called medullary thyroid cancer, pheochromocytoma, and parathyroid gland cancer. It may also cause benign (noncancerous) tumors in the parathyroid glands and adrenal glands. The affected endocrine glands may make high levels of hormones, which can lead to other medical problems such as high blood pressure and kidney stones. An itchy skin condition may also occur. Sipple syndrome is caused by a mutation (change) in a gene called RET. Also called MEN2A, MEN2A syndrome, multiple endocrine adenomatosis type 2A, and multiple endocrine neoplasia type 2A syndrome.