Bone in the marmoset: a resemblance to vitamin D-dependent rickets, type II.

The common marmoset, a New World monkey, requires a large amount of vitamin D3 to maintain its normal growth. This monkey is reported to have an end-organ resistance to 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3). In this study, the bone morphology of marmosets fed a high vitamin D3 diet (intake of vitamin D3, 110 IU/day/100 g of body weight) was compared by X-ray and histological examinations with that of rhesus monkeys (Old World monkey) fed a normal diet (intake of vitamin D3, 5 IU/day/100 g of body weight). Three of 20 marmosets were found by X-ray examination to have osteomalacic changes in their bones despite the high daily intake of vitamin D3, whereas none of the 5 rhesus monkeys showed any signs of osteomalacia. Osteomalacic marmosets had distinct increases in osteoid surface, relative osteoid volume, and active osteoclastic bone resorption, whereas non-osteomalacic marmosets had no increase in osteoid tissues in their bones. None of the marmosets, either osteomalacic or non-osteomalacic, was hypercalcemic despite the extremely high circulating levels of 1 alpha,25(OH)2D3. However, the serum 25-hydroxyvitamin D3 (25OHD3) and 24R,25-dihydroxyvitamin D3 (24R,25(OH)2D3) levels were significantly lower in the osteomalacic than in the non-osteomalacic marmosets. These results suggest that the marmoset is likely to exhibit osteomalacic bone changes despite the high daily intake of vitamin D3. These changes resemble those in vitamin D-dependent rickets, type II.