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

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Abstract
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 1α,25-dihydroxyvitamin D3 (1α, 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 osteomalacica. Osteomalacic marmosets had distinct incrases in osteoid surface, relative osteoid volume, and active osteoclastic bone resorption, whereas nonosteomalacic marmosets had no increase in osteoid tissues in their bones. None of the marmosets, either osteomalacic or nonosteomalacic, was hypercalcemic despite the extremely high circulating levels of 1α,25(OH)2D3. However, the serum 25-hydroxy vitamin D3 (25OHD3) and 24R,25-dihydroxyvitamin D3 (24R,25(OH)2D3) levels were significantly lower in the osteomalacic than in the nonosteomalacic 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.