Genetic Effects of Estrogen Receptor  and Collagen IA1 Genes on the Relationships of Parathyroid Hormone and 25 Hydroxyvitamin D With Bone Mineral Density in Caucasian Women R. Sapir-Koren, G. Livshits, and E. Kobyliansky There is a growing body of evidence that estrogen receptor  (ER) and collagen IA1 (COLIA1) genes may affect bone mineral density (BMD) levels in postmenopausal women. In a recent study we found that the Px haplotype of the ER gene (resulting from combined PvuII and XbaI restriction fragment-length polymorphisms [RFLPs] in intron 1) was associated with low radiographic phalangeal hand BMD in elderly women (62.7  6.5 years of age), of European origin. The combination of the Px haplotype and “s” allele of the COLIA1 gene (MscI RFLP in Sp1 locus) decreased BMD in these women. The major aim of the present study was to investigate whether the genetic effects of these genotypes on cancellous and cortical hand BMD, in the same elderly women (N  122), are possibly mediated through circulating levels of parathyroid hormone (PTH) and/or 25 hydroxyvitamin D [25(OH)D], and may be related to biochemical markers of bone turnover (propeptide of type I procollagen [PICP] and osteocalcin). Multiple regression analyses of age-adjusted cancellous BMD revealed that ER polymorphism and circulating levels of PTH were independent predictors of about 12.9% of its variation. Some 17.9% of cortical BMD variations were attributable to the combined effects of ER polymorphism and plasma concentrations of 25(OH)D, estradiol, and PTH. The significant inverse association between PTH and BMD of both types was further confirmed by association analysis according to categorical subgroups of BMD values, as well by haplotype status. The mean difference in PTH concentrations between subjects carrying the Px haplotype (higher mean) and those lacking it (lower mean) reached 0.59 SD (P  .01). The difference in PTH levels further increased when explored in the 4 subgroups formed by combinations of polymorphic ER and COLIA1 genotypes. Mean PTH of subjects carrying both the Px haplotype and “s” allele was higher by 1.52 SD (P  .001) than in subjects lacking both the Px haplotype and “s” allele. Those carrying both Px haplotype and “s” allele were also characterized by highest mean value of PICP and lowest means of 25(OH)D and BMD (both tissue types). We conclude that in the studied elderly women, the Px haplotype may be involved in causing the phenotypic expression of higher circulating levels of PTH and higher bone turnover, which, in turn, may lead to bone loss. © 2003 Elsevier Inc. All rights reserved. B ONE mineral density (BMD) is a quantitative trait deter- mined by the interaction of genetic, metabolic, and en- vironmental factors, and its diminution is deemed a major risk factor for fractures. To date, several candidate genes have received great attention, among them the collagen IA1 (COLIA1) and estrogen receptor  (ER) genes. 1-8 The CO- LIA1 gene encodes the most abundant bone matrix protein, collagen type I1. Estrogen receptor genes mediate in women the effects of estrogen, probably the major systemic hormone for maintaining normal bone turnover, 9 and its deficiency leads to bone mass loss. 10 While there are some evidence that the ER gene may be involved in regulation of BMD in men, 11,12 the main evidence for its regulatory role of BMD in women derives from studies performed in postmenopausal women of different ethnic origins. 5,7,8,13 We recently conducted haplotype-based association analysis between combined PvuII and XbaI restriction fragment-length polymorphisms (RFLPs) in intron 1 of ER gene and phalan- geal hand BMD, on pedigree data collected from a population of European origin, residing in Russia. 13 We found that the Px haplotype of the ER was associated with low cancellous and cortical BMD in a maternal subgroup, actually comprised of elderly women (62.7  6.5 years of age). The transmission disequilibrium test (TDT) revealed evidence suggestive of a linkage disequilibrium between the Px haplotype of the ER gene and the BMD putative gene in female (but not in male) offspring. Additionally in our elderly women sample, the “s” allele of COLIA1 gene substantially enhanced the influence of the Px haplotype of the ER gene by further reducing BMD in subjects carrying the combined genotypes (Px haplotype and “s” allele). It has been shown that increased/decreased levels of calcio- tropic hormones (parathyroid hormone [PTH] and 25 hy- droxyvitamin D [25(OH)D]), and biochemical indices of bone formation like the carboxyterminal propeptide of type I procol- lagen (PICP), or osteocalcin, may be associated with increased risk for osteoporosis fracture in postmenopausal women, inde- pendently of each other or of BMD. 14-16 The present study was therefore undertaken to evaluate whether the association of the Px haplotype of the intronic ER gene and allele “s” of Sp1 locus in the COLIA1 gene with phalangeal hand BMD could be related to calciotropic hormones and/or biochemical indices of bone formation. Specifically we addressed the following 4 questions: (1) Is there an association between high or low levels of each of the above biochemical indices and low BMD? (2) Is there an association between high or low levels of each of the above biochemical indices and either or both the Px haplotype of the ER gene and the “s” allele of the COLIA1 gene? (3) Is there a specific genotype whose carriers are characterized by a lowest mean BMD and highest (or lowest) circulating levels of From the Research Unit–Human Population Biology, Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel. Submitted August 5, 2002; accepted April 29, 2003. Supported by the Israeli National Science Foundation, “Academia” (agreement no. 544/00), by the Constantiner Institute for Molecular Genetics, Tel Aviv University, and by Strauss Dairies Ltd, Israel. Address reprint requests to Professor G. Livshits, Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978 Israel. © 2003 Elsevier Inc. All rights reserved. 0026-0495/03/5209-0007$30.00/0 doi:10.1016/S0026-0495(03)00187-2 1129 Metabolism, Vol 52, No 9 (September), 2003: pp 1129-1135