Polymorphism at the vitamin D receptor gene was examined in relation to bone mineral density (BMD) at spine, femur, and forearm in 86 monozygotic (MZ) and 39 dizygotic (DZ) adult female twins. All were white, 63 pairs (44 MZ, 19 DZ) were premenopausal, and 43 pairs (31 MZ, 12 DZ) were discordant for age at menopause or use of estrogen.Each individual of the DZ pairs and one individual of MZ pairs was genotyped for Apal, BsmI, and TaqI polymorphism at the vitamin D receptor gene locus using Southern hybridization.Intraclass correlations for BMD in MZ and DZ twin pairs indicated that heritability accounted for over 70% of BMD. There was no relationship between genotype for any of the three polymorphisms and BMD at any skeletal site in the twin population, considered either as a total population, both with and without twins discordant for age at menopause or use of estrogen, or as a premenopausal population. In DZ twin pairs discordant for alleles for the three polymorphisms, no allele was associated with higher or lower BMD.It is concluded that in this population of healthy adult females there was no relationship between these polymorphisms at the vitamin D receptor gene locus and BMD. (J. Clin. Invest. 1994. 94:2130-2134

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The hormonal form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], inhibits the proliferation of T lymphocytes and production of growth-promoting factors (including interleukin-2) (IL2) in CTLL2 murine cells. In this study, we investigated the role of monocytes in this hormone-mediated inhibitory effect, by testing the effects of 1,25-(OH)2D3 on the ability of the mitogenic lectin phytohemagglutinin (PHA) to induce T cell activation in either a monocyte-dependent or phorbol myristate acetate (PMA)-driven (monocyte-independent) system. The results indicate that proliferation of T cells and production of growth-promoting factors are inhibited by 1,25-(OH)2D3 only in the monocyte-dependent system. Preincubation of monocytes with 1,25-(OH)2D3 for various periods of time and subsequent removal of the hormone resulted in inhibition of the PHA-driven proliferation of T cells. Preincubation for 2 h resulted in 20% inhibition, while preincubation for 36 h reduced proliferation to 50% of the control value [no 1,25-(OH)2D3 exposure]. These data suggested that monocytes are important participants in 1,25-(OH)2D3-mediated events. Therefore, we tested the effects of the hormone on the production of IL1, a monocyte-derived product thought to be involved in the induction of IL2 release and the subsequent development of the T cell proliferative response. 1,25-(OH)2D3 inhibited the production of both extracellular and cell-associated immunoreactive IL1 alpha and IL1 beta. Indomethacin, a prostaglandin synthetase inhibitor, did not alter the inhibitory properties of 1,25-(OH)2D3, suggesting that prostaglandins are not responsible for the inhibitory phenomenon. We conclude that part of the ability of 1,25-(OH)2D3 to inhibit T cell proliferation may be due to direct effects on monocytes by down-regulating IL-1 production. However, it is unlikely that the immunoregulatory properties of 1,25-(OH)2D3 on T cells are mediated solely through monocytes, and it is possible that the hormone also exerts its influence directly on T cells.