Summary
McCune-Albright syndrome (MAS) is a rare, genetic, non-inherited condition that causes bone tumors, bone deformity and fractures. The manifestations include polyostotic fibrous dysplasia, café au lait spots, and precocious puberty.
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McCune-Albright syndrome (MAS) is a rare condition that results from a spontaneous, non-inherited mutation in the Gs gene. The manifestations include polyostotic fibrous dysplasia, bone fractures, café au lait (hyperpigmented) skin spots, precocious onset of puberty, and variable hyperactivity of the endocrine glands.
Mutation of the GS gene in chromosome 20q13 occurs early in development, and results in a mosaic of abnormal and mutated cells. The manifestations of MAS in each individual depend upon the extent and distribution of abnormal cells. Abnormal and prolonged activation of multiple peripheral endocrine glands occurs even while the necessary stimulatory pituitary hormones may be absent. Precocious puberty, with onset of breast development, pubic hair, and the onset of menses as early as the first few months of life may occur in females. Other manifestations include acromegaly, hyperthyroidism, hyperprolactinemia, and others.
Frequently involved bones include the femur, the tibia, the facial skeleton, and the ribs. Bone fragility and associated fractures are common, and weight-bearing bones may suffer multiple fractures. In the proximal femurs, multiple successive cortical microfractures may result in characteristic bowing of the proximal end of the bone into a "shepherd's crook" deformity.
Clinical signs of sarcomatous degeneration include pain and swelling at the site of the lesion. The most reliable radiographic sign is extension of the lesion through the cortex into the surrounding soft tissues. Since osteosarcoma is the most common histologic type of sarcoma that may occur, bone formation within the soft tissue mass would be a particularly worrisome sign.