The Williams syndrome is a disease in which supravalvular aortic stenosis, an elfin facies, mental retardation and other congenital defects are sometimes associated with abnormal vitamin D and calcium metabolism. Whereas some patients have been reported to show increased sensitivity to vitamin D or an exaggerated response of serum 25-hydroxyvitamin D {25(OH)D} to administration of vitamin D and to have hypercalcemia caused by increased circulating 1,25-dihydroxyvitamin D{1,25(OH)2D} in infancy and early childhood, most patients have normal calcium metabolism and normal values for circulating 25(OH)D and 1,25(OH)2D. We propose to carry out further studies of vitamin D metabolism to elucidate the mechanism(s) for abnormal vitamin D metabolism. We will determine the response of serum 1,25(OH)2D to administration of 1,25(OH)2D3. Measurement of the 1,25(OH)2D in the patients compared to normal subjects will be the primary outcome.