Here we review and extend a new unitary model for the pathophysiology of involutional osteoporosis that identifies estrogen (E) as the key hormone for maintaining bone mass and E deficiency as the major cause of age-related bone loss in both sexes. Also, both E and testosterone (T) are key regulators of skeletal growth and maturation, and E, together with GH and IGF-I, initiate a 3- to 4-yr pubertal growth spurt that doubles skeletal mass. Although E is required for the attainment of maximal peak bone mass in both sexes, the additional action of T on stimulating periosteal apposition accounts for the larger size and thicker cortices of the adult male skeleton. Aging women undergo two phases of bone loss, whereas aging men undergo only one. In women, the menopause initiates an accelerated phase of predominantly cancellous bone loss that declines rapidly over 4-8 yr to become asymptotic with a subsequent slow phase that continues indefinitely. The accelerated phase results from the loss of the direct restraining effects of E on bone turnover, an action mediated by E receptors in both osteoblasts and osteoclasts. In the ensuing slow phase, the rate of cancellous bone loss is reduced, but the rate of cortical bone loss is unchanged or increased. This phase is mediated largely by secondary hyperparathyroidism that results from the loss of E actions on extraskeletal calcium metabolism. The resultant external calcium losses increase the level of dietary calcium intake that is required to maintain bone balance. Impaired osteoblast function due to E deficiency, aging, or both also contributes to the slow phase of bone loss. Although both serum bioavailable (Bio) E and Bio T decline in aging men, Bio E is the major predictor of their bone loss. Thus, both sex steroids are important for developing peak bone mass, but E deficiency is the major determinant of age-related bone loss in both sexes.

Sex steroids and the construction and conservation of the adult skeleton.

See related commentary by Kanis, page [1829][1]

Since the publication of the Osteoporosis Canada guidelines in 2002, there has been a paradigm shift in the prevention and treatment of osteoporosis and fractures. [1][2],[2][3] The focus now is on preventing fragility fractures and their negative

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2010 clinical practice guidelines for the diagnosis and management of osteoporosis in Canada: summary

Quantitative ultrasound (QUS) methods have been introduced in recent years for the assessment of skeletal status in osteoporosis. The performance of QUS techniques has been evaluated in a large number of studies. Reviewing existing knowledge, an international expert panel formulated the following consensus regarding the current status of this technology. To date, evidence supports the use of QUS techniques for the assessment of fracture risk in elderly women. This has been best established for water-based calcaneal QUS systems. Future studies should include the predictive validity of other QUS systems. Additional clinical applications of QUS, specifically the assessment of rates of change for monitoring disease progression or response to treatment, require further investigation. Its low cost and portability make QUS an attractive technology for assessing risk of fractures in larger populations than may be suitable or feasible for bone densitometry. Additional investigations that assess innovative QUS techniques in well defined research settings are important to determine and utilize the full potential of this technology for the benefit of early detection and monitoring of osteoporosis.

Quantitative ultrasound techniques for the assessment of osteoporosis : Expert agreement on current status

This study, based on data from the National Osteoporosis Risk Assessment, examined the effects of different treatment thresholds on fracture risk within a year after a measurement of bone mineral density (BMD). BMD is thesingle most important predictor of osteoporotic fractures in postmenopausal women having no previous fractures. The study population included 149,524 white postmenopausal women 50 to 104 years of age. At baseline, BMD was measured by peripheral bone densitometry at the heel, finger, or forearm. Fracture risk was followed over the next 12 months. A total of 2340 new osteoporotic fractures were reported by 2259 women. Hip fractures made up 17% of the total. As shown in Figure 1, lower baseline BMD values were associated with higher fracture rates (the number of women with fracture per 1000 person-years of follow up). Fracture rates were highest in women with the lowest T scores. More than 80% of women who reported having a fracture within 12 months had peripheral T scores higher than -2.5, and two thirds had T scores exceeding -2.0. Fracture rates were highest in these women but they occurred in only 18% of osteoporotic fractures and 26% of hip fractures. According to treatment guidelines formulated by the National Osteoporosis Foundation, 22.6% of women had T scores of 2.0 or less or -1.5 or less accompanied by 1 or more clinical risk factors. Fracture rates were lower in these women, but they constituted 45% of all osteoporotic fractures and 53% of hip fractures. It seems unlikely that a substantial reduction of osteoporotic fractures in postmenopausal women could be achieved solely by treating women with T scores of -2.5 or less. More attention must be given to women with moderate loss of bone mass who are nevertheless at increased risk of future fracture. The authors believe that nonpharmacologic measures such as weight-bearing exercise, strength training, and a healthy diet with adequate calcium should be tried as an initial measure.

Bone mineral density thresholds for pharmacologic intervention to prevent fractures

Osteoporosis is a common multifactorial disorder of reduced bone mass. The disorder in its most common form is generalized, affecting the elderly, both sexes, and all racial groups. Multiple environmental factors are involved in the pathogenesis. Genes also play a major role as reflected by heritability of many components of bone strength. Quantitative phenotypes in bone strength in the normal population do not conform to a monogenetic mode of inheritance. The common form of osteoporosis is generally considered to be a polygenic disorder arising from the interaction of common polymorphic alleles at quantitative trait loci, with multiple environmental factors. Finding the susceptibility genes underlying osteoporosis requires identifying specific alleles that coinherit with key heritable phenotypes in bone strength. Because of the close correspondence among mammalian genomes, identification of the genes underlying bone strength in mammals such as the mouse is likely to be of major assistance in human studie...

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Genetics of Osteoporosis

Bone mass and bone turnover are under genetic control. Restriction fragment length polymorphisms (RFLPs) at the vitamin D receptor (VDR) gene locus have been recently correlated to bone mineral density (BMD) and rate of bone loss. However, agreement on this relationship is not universal. The existence of ethnical and environmental differences between populations, a health-based selection bias in several previous studies, and the involvement of other genes could explain these discordant findings. In this study, we examined the relationship of VDR and estrogen receptor (ER) gene RFLPs with lumbar spine and upper femur BMD in 426 Italian postmenopausal women, 57.7 +/- 0.4 yr old (144 normal, 106 osteopenic, and 176 osteoporotic). VDR gene RFLPs for ApaI, Bsm I, and TaqI restriction endonucleases and ER RFLPs for PvuII and XbaI restriction endonucleases were assessed by Southern blotting analysis and were indicated, respectively, as A-a, B-b, T-t, P-p, and X-x (uppercase letters signifying the absence and lowercase letters the presence of the restriction site). After correcting for potential confounding factors (age, height, weight, age since menopause, osteophytosis, and facet joint osteoarthritis), a statistically significant VDR genotype effect on lumbar BMD (P = 0.01, analysis of covariance), but not on femoral BMD, was detected, with subjects in AABBtt genotype showing a 13% lower BMD than those with aabbTT genotype (P < 0.05, Tukey's test). Moreover, a statistically significant prevalence of AABBtt genotype in osteoporotics, and of AabbTT and aabbTT genotypes in nonosteoporotics, were detected. Conversely, there was no significant relationship of ER genotype to either lumbar or femoral BMD, even though a trend for higher BMD values in women with the ER PP genotype (with respect to those with ER pp genotype) was detected. When mean lumbar BMD was calculated for women grouped by ER and VDR genotype, we observed a significant difference between those within the 2 opposite associations AABBtt-PPXX and aabbTT-ppxx (0.71 +/- 0.05 vs. 0.97 +/- 0.03 g/cm2, P < 0.05 Tukey's test). These results are consistent with a segregation of the VDR AABBtt genotype with a higher risk of developing osteoporosis, in the Italian female population. The introduction of another variable, the ER genotype, in the analysis of VDR genetic determination of BMD, may represent a useful model in the identification of patients at risk of developing a multigenic disorder like osteoporosis.

Vitamin D and Estrogen Receptor Allelic Variants in Italian Postmenopausal Women: Evidence of Multiple Gene Contribution to Bone Mineral Density

Several studies have shown that bone mass and bone turnover are genetically determined. This genetic component is thought to be mediated in part by polymorphisms at the vitamin D receptor (VDR) locus, even though the underlying molecular mechanisms are still unknown. To evaluate a possible site of differential action of the VDR gene alleles we examined their correlation with intestinal calcium absorption in 120 Caucasian postmenopausal women (aged 61 ± 0.6 years). VDR gene polymorphisms for Apa I, Bsm I, and Taq I restriction endonucleases were assessed by Southern blotting analysis. The most common genotypes observed in our population were AaBbTt (37%), AABBtt (20%), aabbTT (15%), AabbTT (15%), and AABbTt (9%). Although there was some evidence of 13% higher lumbar BMD values in aabbTT genotype with respect to AABBtt genotype, this difference of approximately 0.1 g/cm2 did not reach statistical significance, possibly because of the limited number of observations. On the contrary, no relationship was found between genotypes and femoral neck BMD values. Intestinal calcium absorption was significantly lower in BB and tt genotypes than, in bb and TT genotypes, respectively, and in AABBtt genotype than in either aabbTT or AaBbTt genotypes (P= 0.0015 ANOVA). No significant differences in intact PTH, alkaline phosphatase, 25OHD3, and 1,25(OH)2D3 were found among subjects with different VDR genotypes. These results are consistent with a possible role of VDR alleles on intestinal calcium absorption.

Vitamin D Receptor Genotypes and Intestinal Calcium Absorption in Postmenopausal Women

Speed of sound (SOS) and broadband ultrasound attenuation (BUA) of ultrasound (US) in bone have been proposed as alternatives to radiation-based methods for the quantitative assessment of osteoporosis. However, the usefulness of US in monitoring response to treatment in osteoporotic patients has yet to be defined. To compare US with bone mineral density (BMD), we studied 112 osteoporotic women (age range 50–64 years). Seventy-eight of them were treated with salmon calcitonin nasal spray (CT; 200 IU/day, 1 month on and 1 month off) and calcium (500 mg/day); 34 patients were given only calcium. One hundred and four women complied with treatment throughout the 2-year study period. At baseline and after 1 and 2 years we measured BMD at lumbar spine by dual-energy X-ray absorptiometry (DXA), and SOS, BUA and Stiffness index, by an Achilles ultrasound unit. Moreover, biochemical markers of bone turnover (alkaline phosphatase, osteocalcin and hydroxyproline) were also measured at baseline and after 6, 12 and 24 months. In the calcitonin-treated group at the end of the study period BMD had increased by 1.99%, SOS by 0.20%, BUA by 0.88% and Stiffness by 2.12%. By contrast in the calcium-treated group all parameters had decreased (BMD, −2.66%; SOS, −0.55%; BUA, −3.30%; Stiffness, −6.0%) by the end of the study period. The differences between groups were significant for BMD, SOS and Stiffness. At baseline a significant, but weak correlation was found between BMD and US parameters. The correlation coefficients between percentage changes at the end of the study period, in BMD and in SOS, BUA and Stiffness, were all significant (p<0.001), being 0.41, 0.53 and 0.57 respectively. In conclusion, ultrasound measurements carried out in conjunction with BMD measurements will yield a more comprehensive assessment of skeletal status and may be helpful in monitoring the response to treatment in osteoporotic patients.

Ultrasound parameters in osteoporotic patients treated with salmon calcitonin: a longitudinal study.

Transdermal estrogen therapy is now an accepted form of treatment for postmenopausal osteoporosis. Ninety postmenopausal osteoporotic women were randomized to receive either transdermal estrogen (0.05 mg/day 17β-estradiol) and calcium (n = 45) or calcium alone (n = 45). The study period was 2 years. Bone mineral density (BMD) at the lumbar spine (by dual-energy X-ray absorptiometry [DXA]) and markers of bone turnover (alkaline phosphatase, osteocalcin, hydroxyproline, pyridinoline cross-links) were assessed at baseline and after 1 and 2 years. In the estrogen-treated group, BMD showed a significant increase (p < 0.001) both after 1 and 2 years, with a reduction in biochemical markers. To investigate the effectiveness of estrogen treatment of postmenopausal osteoporosis in relation to bone turnover, we also divided the patients on the basis of bone turnover, as assessed by measurement of whole body retention (WBR) of99mTc-methylene diphosphonate. WBR revealed that 26 patients had high bone turnover (HT) and 55 had low bone turnover (LT). The response to estrogen was greater in the HT patients than in the LT patients; in fact BMD increased by 5.7 and 6.6% in HT patients and by 2.6 and 2.7% in LT patients after 1 and 2 years, respectively. In conclusion, the present study demonstrates that, while the BMD decreases in the patients treated with calcium alone, 2-year treatment with transdermal estrogen increases axial BMD and that the response to estrogen treatment is influenced by bone turnover. Therefore, the evaluation of bone turnover may be useful to identify those postmenopausal osteoporotic women who may especially benefit from treatment with estrogen.

S Martini

Papers

Vitamin D and Estrogen Receptor Allelic Variants in Italian Postmenopausal Women: Evidence of Multiple Gene Contribution to Bone Mineral Density

Vitamin D Receptor Genotypes and Intestinal Calcium Absorption in Postmenopausal Women

Ultrasound parameters in osteoporotic patients treated with salmon calcitonin: a longitudinal study.

The usefulness of bone turnover in predicting the response to transdermal estrogen therapy in postmenopausal osteoporosis

Quantitative ultrasound in the assessment of skeletal status in uremic patients.