Impact of endocrine hyperfunction and phosphate wasting on bone in McCune-Albright syndrome

Skin dysplasia, as cafe-au-lait spots, bone fibrous dysplasia and peripheral endocrinopathies are the main clinical features of McCune-Albright syndrome (MAS). This illness is due to activating mutations of the G(s)alpha protein and is spread with a mosaic pattern in affected tissues that consist of intermixed areas of normal and mutated cells. Peripheral endocrine secretion, free of hypothalamic pituitary control, is the hallmark of the endocrine syndromes: precocious puberty, Cushing's syndrome, hyperthyroidism and gigantism/acromegaly. In addition, phosphate wasting as hyperphosphaturia is often present. The impact of hormonal hypersecretion and phosphate loss on the bones of patients with MAS is poorly understood both in normal and fibrous bone tissue. As hypercortisolism and hyperthyroidism increase bone resorption, hyperestrogenism and growth hormone hypersecretion stimulate bone growth and mineralization, and phosphate wasting reduces bone mineral content. All these actions can be exerted at varying times and degrees in a single patient on lesional and non-lesional bones. Sonographic evidence of multiple diffused hyperechogenic spots in the testes of patients with MAS do not seem to be related to alterations in calcium-phosphate metabolism but rather to zonal dysplasia/hyperplasia of testicular tissue.