McCune-Albright syndrome (MAS) is a disorder that affects the skin, skeleton, and certain endocrine organs (hormone-producing tissues). Cafe-au-lait spots of the skin are common and are usually the first apparent sign of MAS. The main skeletal feature is fibrous dysplasia, which ranges in severity and can cause various complications. Early skeletal symptoms may include limping, pain, or fracture. Endocrinous features may include precocious puberty especially in girls (resulting of estrogen excess from ovarian cysts), excess growth hormone; thyroid lesions with possible hyperthyroidism; renal phosphate wasting, and, rarely, Cushing syndrome caused by an excess of the hormone cortisol produced by the adrenal glands, which are small glands located on top of each kidney. MAS is not inherited. MAS is caused by a somatic genetic change in a gene called GNAS, which is acquired after an egg is fertilized and only affects some of the body's cells and tissues.