Supravalvular aortic stenosis with parafollicular cell (C-cell) hyperplasia.

Autopsy examination of a patient with well-documented supravalvular aortic stenosis and other characteristic features of the idiopathic infantile hypercalcemia syndrome revealed previously unreported hyperplasia of parafollicular cells (C cells). Immunohistochemical analysis demonstrated up to 30 calcitonin-containing cells per high power field, whereas normal glands contain only 4 to 10 cells per low power field in areas of highest concentration. The parathyroid glands were found to be normal both grossly and microscopically, whereas the bones showed thickened trabeculas, normal Haversian canals and no apparent increase in osteoblast or osteoclast activity, suggesting normal parathyroid hormone, but increased thyrocalcitonin activity. We suggest that C-cell hyperplasia has occurred in response to a persistent, rather than transient, elevation in serum calcium levels and that thyrocalcitonin function is augmented, rather than impaired in this disorder. The primary biochemical defect promoting hypercalcemia remains to be clarified, as well as the role, if any, such a defect plays in producing significant pathology in the central nervous system and in the cardiovascular, renal and skeletal systems.