Two siblings with vitamin-D-dependent rickets type II: no recurrence of rickets for 14 years after cessation of therapy.

Rickets in a 3-year-old boy and his 1-year-old sister, both with alopecia, was cured by treatment with 50,000 IU of vitamin D2 daily for 2 years and did not recur within 14 years after cessation of therapy. A diagnosis of vitamin-D-dependent rickets type II was made in these patients at the ages of 20 and 18 years based on the findings that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] did not inhibit DNA biosynthesis in phytohaemagglutinin-stimulated lymphocytes and that cultured skin fibroblasts showed impaired nuclear uptake and normal cytosol binding of [3H]1,25(OH)2D3. Surprisingly, the serum 1,25(OH)2D levels of these patients were high and their serum 24,25-dihydroxyvitamin D levels were low, although neither patient showed any symptoms except alopecia. The presence of vitamin D metabolite imbalances in the absence of rickets in these patients might be explained by differences in sensitivity to 1,25(OH)2D3 of bone formation and vitamin D metabolism. In addition, changes of sensitivity to treatment with vitamin D derivatives might be a consequence of differentiation of target cells. From the present findings, it is suggested that in this disease treatment with a sufficient dose of vitamin D derivatives should be initiated in the active phase of rickets.