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The clinical syndrome that results from decreased secretion of thyroid hormone from the thyroid gland. It leads to a slowing of metabolic processes and in its most severe form to the accumulation of mucopolysaccharides in the skin, causing a nonpitting edema termed myxedema. Cretinism is the congenital form leading to abnormalities of intellectual and physical development. (Bennett, et al., Cecil Textbook of Medicine, 20th ed)