as a fellow, he participated in the first chemical synthesis of 1,25-dihydroxyvitamin d3 and 1α-hydroxyvitamin d3 to treat renal osteodystrophy, hypoparathyroidism, vitamin d dependent rickets type i, and osteoporosis. furthermore, he elucidated the pathophysiology of hereditary vitamin d-dependent rickets which involves defective vitamin d metabolism, and the pathophysiological mechanisms of x-linked hypophosphatemic rickets.