Heterogeneity of bone mineral density across skeletal sites and its clinical implications

WHOLE BODY AND REGIONAL BONE MINERAL CONTENT AND DENSITY IN WOMEN AGED 20-75 YEARS

BACKGROUND

Dual-energy X-ray absorptiometry (DXA) allows measurement of whole body (WB) and regional bone mineral content (BMC) and density (BMD).

OBJECTIVE

To measure WB and regional bone area, BMC and BMD (arms, legs, ribs and pelvis) in women of different ages.

SUBJECTS AND METHODS

140 women participated (age range 20-75 yrs). Three subgroups were built: 20-44 yr (30 premenopausal women), 45-59 (80 women), and 60-75 (30 women). WB DXA was performed on a Hologic QDR 4500 A bone densitometer (Hologic Inc., Bedford MA). WB BMD T-scores were calculated by using the manufacturer-provided and the NHANES 1999-2004 reference databases, while the WB BMC Z-scores - based on the latter. Statistical analysis was performed on an IBM SPSS Statistics 19.0 for Windows platform (Chicago, IL).

RESULTS

WB BMC and BMD Z-scores were consistently lower than the reference databases showing a difference of about 0.4 - 0.5 SD. The arms, legs and ribs lost more BMC after the age of 50-55, while the pelvis - much earlier. The total decreases in BMC were highest in the pelvis (26.36 %), followed by the arms (16.81 %) and whole body (15.91 %), while the bone area decreased mostly in the pelvis (13.23 %).

CONCLUSION

The age-related declines in regional BMC, bone areas and BMD follow different patterns in appendicular and axial bones.

Effect of simulated early weight bearing on micromotion and pullout strength of uncemented distal femoral stems

The effect of simulated early weight bearing on both micromotion and pullout strength of uncemented distal femoral stems was evaluated in this study. The effect of stem endosteal contact and bone quality on implant pullout strength was also analyzed. A randomized matched-pair study was performed using 8 bilateral pairs of fresh human cadaveric femoral specimens. Each specimen pair was dual-energy x-ray absorptiometry scanned, uniformly implanted, fluoroscopically imaged, and randomly assigned to the cycled or uncycled group. The cycled group received 5000 cycles of axial compressive loading (to 700 N) and the contralateral side was not cycled. Micromotion was monitored during cycling and compared with a failure threshold (150 µm), and all implants underwent direct axial distraction (pullout) testing. During cycling, minimal micromotion was observed with an asymptotic decrease in differential motion between the first and last 50 cycles. Both cycled and uncycled groups demonstrated no statistical difference in average pullout force (4888±2124 N vs 4367±1154 N; P=.43). The percentage of cortical contact for each implant was determined from panoramic fluoroscopy images using digital image analysis software. Contact area for the distal third of the stem showed the highest correlation with pullout force and with predicting pullout force. Bone quality did not correlate with pullout force (r(2)=0.367) or stem contact area (r(2)=0.394). In sum, press-fit uncemented femoral stems did not loosen or demonstrate decreased pullout strength with early weight bearing simulated by cyclical axial compressive loading.

Bone tissue composition varies across anatomic sites in the proximal femur and the iliac crest

The extent to which bone tissue composition varies across anatomic sites in normal or pathologic tissue is largely unknown, although pathologic changes in bone tissue composition are typically assumed to occur throughout the skeleton. Our objective was to compare the composition of normal cortical and trabecular bone tissue across multiple anatomic sites. The composition of cadaveric bone tissue from three anatomic sites was analyzed using Fourier transform infrared imaging: iliac crest (IC), greater trochanter (GT), and subtrochanteric femur (ST). The mean mineral:matrix ratio was 20% greater in the subtrochanteric cortex than in the cortices of the iliac crest (p = 0.004) and the greater trochanter (p = 0.02). There were also trends toward 30% narrower crystallinity distributions in the subtrochanteric cortex than in the greater trochanter (p = 0.10) and 30% wider crystallinity distributions in the subtrochanteric trabeculae than in the greater trochanter (p = 0.054) and the iliac crest (p = 0.11). Thus, the average cortical tissue mineral content and the widths of the distributions of cortical crystal size/perfection differ at the subtrochanteric femur relative to the greater trochanter and the iliac crest. In particular, the cortex of the iliac crest has lower mineral content relative to that of the subtrochanteric femur and may have limited utility as a surrogate for subtrochanteric bone.

Genome-wide association study identifies ALDH7A1 as a novel susceptibility gene for osteoporosis

Osteoporosis is a major public health problem. It is mainly characterized by low bone mineral density (BMD) and/or low-trauma osteoporotic fractures (OF), both of which have strong genetic determination. The specific genes influencing these phenotypic traits, however, are largely unknown. Using the Affymetrix 500K array set, we performed a case-control genome-wide association study (GWAS) in 700 elderly Chinese Han subjects (350 with hip OF and 350 healthy matched controls). A follow-up replication study was conducted to validate our major GWAS findings in an independent Chinese sample containing 390 cases with hip OF and 516 controls. We found that a SNP, rs13182402 within the ALDH7A1 gene on chromosome 5q31, was strongly associated with OF with evidence combined GWAS and replication studies (P = 2.08×10⁻⁹, odds ratio = 2.25). In order to explore the target risk factors and potential mechanism underlying hip OF risk, we further examined this candidate SNP's relevance to hip BMD both in Chinese and Caucasian populations involving 9,962 additional subjects. This SNP was confirmed as consistently associated with hip BMD even across ethnic boundaries, in both Chinese and Caucasians (combined P = 6.39×10⁻⁶), further attesting to its potential effect on osteoporosis. ALDH7A1 degrades and detoxifies acetaldehyde, which inhibits osteoblast proliferation and results in decreased bone formation. Our findings may provide new insights into the pathogenesis of osteoporosis.

Osteoporosis is a major health concern worldwide. It is a highly heritable disease characterized mainly by low bone mineral density (BMD) and/or osteoporotic fractures. However, the specific genetic variants determining risk for low BMD or OF are largely unknown. Here, taking advantage of recent technological advances in human genetics, we performed a genome-wide association study and follow-up validation studies to identify genetic variants for osteoporosis. By examining a total of 11,568 individuals from Chinese and Caucasian populations, we discovered a susceptibility gene, ALDH7A1, which is associated with hip osteoporotic fracture and BMD. ALDH7A1 might inhibit osteoblast proliferation and decrease bone formation. Our finding opens a new avenue for exploring the pathophysiology of osteoporosis.

Bone mineral density measurement at both spine and hip for diagnosing osteoporosis in Japanese patients

In Japan, spinal dual-energy X-ray absorptiometry (DXA) has been commonly performed for diagnosing osteoporosis but scanning the proximal femur is not done widely. The latest Japanese guidelines for prevention and treatment of osteoporosis, revised in 2006, recommend bone mineral density (BMD) measurement at both spine and hip for diagnosing osteoporosis, although there have been no reports that proved the necessity of those measurements. One thousand forty-one women and 485 men with clinical suspicion of osteoporosis were enrolled in this study, and DXA was performed at both spine and hip. The proportions of the patients who had inconsistency between diagnosis of osteoporosis from spinal DXA and that of hip were estimated. As a result, 22% of women and 15% of men had an inconsistency with the diagnosis of osteoporosis using DXA at each measurement site. There was inconsistency in diagnosing osteoporosis using DXA at the spine and proximal femur measurement sites. Because spine and femoral DXA measurements complement each other in the diagnosis of osteoporosis, BMD measurement at both spine and hip should be performed for all Japanese patients who are suspected osteoporosis, regardless of age and sex.

First update of the Lebanese guidelines for osteoporosis assessment and treatment

With the demographic explosion, the human, social, and economic costs of osteoporosis in developing countries, including the Middle East, will continue to rise. In 2002, the Lebanese Guidelines for Osteoporosis Assessment and Treatment were developed to optimize quality of osteoporosis care in Lebanon and the region. They were endorsed by 5 Lebanese medical scientific societies, and by the Eastern Mediterranean Regional Office branch of the World Health Organization (WHO). In April 2006, the Lebanese Society for Osteoporosis and Metabolic Bone Disorders (OSTEOS) led an initiative to update several recommendations detailed in the original document, based on relevant new local and international data. Data from a population-based sample of elderly Lebanese validated the following recommendations: fracture risk assessment, expressed as relative risk per standard deviation (RR/SD) decrease, was comparable in Lebanese subjects to similarly derived estimates from Western studies; the use of the NHANES database (hip), and the densitometer American database (spine) was as good, if not superior to the use of a Lebanese database for identifying subjects with prevalent vertebral fractures. The original recommendation regarding the use of a gender-specific western database, densitometer for spine and NHANES for T-score derivation for men, remains unchanged. For skeletal site selection, the update recommends measuring the spine and hip for women < or =65 yr, hip only for subjects >65 yr, and adding the forearm in conditions associated with cortical bone loss or in the case of inability to measure axial sites. The original recommendations for conservative management in premenopausal women were reiterated. This First Update of the Lebanese Osteoporosis Guidelines validates previous recommendations using evidence from a population-based sample of elderly Lebanese, and lays the ground for transitioning the Lebanese Osteoporosis Guidelines to the WHO global fracture risk assessment model.

Peripheral bone densitometry: Clinical applications

Technologies for the measurement of bone mineral density and other parameters of bone strength at peripheral skeletal sites have been studied since the 1960s. Single-energy Photon Absorptiometry (SPA), Radiographic Absorptiometry (RA), Radiogrametry (RG), Single-energy X-ray Absorptiometry (SXA), Peripheral Dual-energy X-ray Absorptiometry (pDXA), and Quantitative Ultrasonometry (QUS) have been successively evaluated. These technologies and their clinical applications are discussed in this article. The available scientific evidence supports the clinical use of these technologies at peripheral skeletal for assessment of fracture risk. Peripheral measurements other than the 33% (one-third) radius by DXA cannot be used to diagnose osteoporosis according to current standards. Peripheral skeletal sites are not clinically useful for monitoring changes in BMD with natural evolution of the disease and its treatment. Peripheral BMD measurement can theoretically be used to screen patients for selection to central DXA testing, although device-specific cut-points should be developed before this is implemented. When central DXA testing is not available, peripheral BMD testing may be considered to identify individuals who might benefit from pharmacological intervention.

Age-related bone mineral density, bone loss rate, prevalence of osteoporosis, and reference database of women at multiple centers in China

Our study surveyed age-related bone mineral density (BMD), bone loss rate, and prevalence of osteoporosis in women at multiple research centers in China. Survey results were used to establish a BMD reference database for the diagnosis of osteoporosis in Chinese women nationwide. We used dual-energy X-ray absorptiometry bone densitometers to measure BMD at posteroanterior (PA) lumbar spine (L1-L4; n=8142) and proximal femur (n=7290) in female subjects of age 20-89 yr from Beijing, Shanghai, Guangzhou, Chengdu, Nanjing, and Jiaxing. A cubic regression-fitting model was used to describe the change of BMD with age at various skeletal sites. Peak BMD occurred between 30 and 34 yr of age for femur neck and total femur, and between 40 and 44 yr for spine and trochanter measurement sites. Young adult (YA) BMD values (mean and standard deviation [SD], calculated as the average BMD in the age range of 20-39, were 1.116+/-0.12, 0.927+/-0.12, 0.756+/-0.11, and 0.963+/-0.13 g/cm2 at PA spine, femoral neck, trochanter, and total femur, respectively. The BMD of 85-yr-old women reflected a loss of 32% at the spine and 30-35% at femur measurement sites. The prevalence of osteoporosis, defined as a BMD of <or=-2.5 SDs from YA values established in this study, in female subjects of age 50 yr or older, was 28% for the spine, 15% for any femur site, and 31% for any spine or femur site. This study provides important information for formulating osteoporosis prevention and treatment strategies in Chinese women, and it establishes a reliable BMD reference database for the diagnosis of osteoporosis of Chinese women nationwide.

Complex segregation analysis accounting for GxE of bone mineral density in European pedigrees selected through a male proband with low BMD

Osteoporosis is a common multifactorial disorder characterized by low bone mass (BMD) and high susceptibility to low-trauma fractures. Family and twin studies have found a strong genetic component in the determination of BMD, but the mode of inheritance of this trait is not yet fully understood. BMD is a complex trait whose expression is confounded by environmental influences and polygenic inheritance. Detection of potential gene-environment interactions is of great interest in the determination of bone health status. Here we have conducted segregation analyses, using the regressive class D models, in a sample of 100 European pedigrees (NEMO) with 713 subjects (524 measured for phenotypes) identified via a male with low BMD values at either the Lumbar Spine or the Femoral Neck. Segregation analyses were conducted on the residuals of LS-BMD and FN-BMD adjusted for gender, age and BMI. We tested for gene-covariate (GxE) interactions, and investigated the impact of significant GxE interactions on segregation results. Without GxE a major effect was found to be marginally significant in LS-BMD and highly significant in FN-BMD. For both traits the Mendelian hypothesis was rejected. Significant Age x gene and BMI x gene interactions were revealed. Accounting for GxE increased statistical evidence for a major factor in LS-BMD, and improved the fit of the data to the Mendelian transmission model for both traits. The best fitting models suggested a codominant major gene accounting for 45% (LS-BMD) and 44% (FN-BMD) of the adjusted BMDs. However, substantial residual correlations were also found, and these remained highly significant after accounting for the major gene.

Smokeless tobacco use accelerates age-related loss of bone mineral density among older women in a multi-ethnic rural community

Cigarette smoking is a recognized risk factor for low bone mineral density (BMD) and osteoporosis. Despite the prevalence of smokeless tobacco (ST) use by women in some areas of the United States, minority groups in the United Kingdom, and populations in South Asia and Africa, no data exist to evaluate its effect on bone health. The objective of the study is to identify risk factors for low BMD among older women in a multi-ethnic population, with particular attention to smoking and ST use. Data were collected in Robeson County, North Carolina. ST use from childhood is common among women in this community. Two hundred-forty women aged 60 years and older (approximately equal numbers of African Americans, Native Americans and whites) were recruited at a variety of community events to obtain a cross-section of the demographic composition of the county. The main outcome was BMD measured in the heel using a portable dual energy x-ray absorptiometry. Twenty-nine percent of women were current or former smokers, and 26% current or former ST users. Increased BMD was predicted by greater body mass index, estrogen use in the past year, and African American and Native American ethnicity. There was a significant interaction between ST use and age, and between smoking and nutritional supplement use. BMD declined with age; the decline with age was greater for women who were current or former ST users than for those who never used ST. Women who formerly smoked and did not use supplements had a decreased BMD. ST should be considered as an additional risk factor for osteoporosis in populations where its use is prevalent.

Osteoporosis in a population from medieval Norway

Modern populations from Norway and England differ in their experience of osteoporosis, the former showing lower bone mineral density (BMD) and a higher fragility fracture rate. The aim of the present work was to investigate whether this was also the case during the Middle Ages. Age-dependent loss of BMD in the proximal femur was assessed using dual X-ray absorptiometry (DXA) in male and female adult skeletons from a cemetery in the medieval town of Trondheim, Norway. Fracture prevalence was also investigated. Results were compared with those previously reported for a skeletal series from Wharram Percy, a deserted medieval village in England. Results indicate that peak BMD and patterns of age-related loss of BMD in the Norwegian and the English group were similar. Among females, the prevalence of osteoporotic fractures was greater in the Norwegian than in the English population. The BMD results suggest that differences in BMD between English and Norwegians are of recent origin, although given the fairly modest sample sizes, further work is needed to confirm this. Reasons for the greater prevalence of osteoporotic fractures in women in the Norwegian skeletal series are unclear, but the colder climate and greater frequency of hard surfaces may have meant that falls were more frequent, and when they occurred, were more likely to result in fractures than in the rural English group.

Prevalence of low central bone mineral density in a Bulgarian female referral population: a pilot study

Osteoporosis is one of the most important health problems among elderly women. The prevalence of central osteoporosis in Bulgaria is still unknown. We tried to retrospectively determine the prevalence of osteopenia and osteoporosis at the spine and hip in a female referral population. Bulgarian women (2,600) aged group 25-87 years referred for bone densitometry screening were included. Information about known risk factors for low bone mass was recorded. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (Hologic QDR 4500 A) at the lumbar spine (2,547 participants, 1,954 of whom were postmenopausal) and left hip (723 participants, 605 of whom were postmenopausal). T-scores were calculated from Hologic-provided and own Bulgarian peak BMD data (the latter based on 122 healthy premenopausal 25- to 39-year-old women). Peak lumbar spine BMD was 0.994 g/cm2 (SD 0.095 g/cm2), and thus lower than the manufacturer-provided value of 1.047 g/cm2. The peak BMD of the total hip was 0.959 g/cm2 (SD 0.129 g/cm2) and thus higher than the manufacturer-provided BMD of 0.942. T-scores differed according to the database used. The osteoporosis threshold of -2.5 SD was reached at the spine in the age group 70-74 years. Left hip T-scores showed a much slower decline with age. In women aged 50 and older the prevalence of osteoporosis reached 37.31% at the spine, and 16.14% at the left hip. Osteopenia was found in 39.74% at the spine and in 65.57% at the total hip. This is the first Bulgarian study looking for the prevalence of central osteoporosis in a female referral population. It may become the starting point for future epidemiological work.

A frequent regulatory variant of the estrogen-related receptor alpha gene associated with BMD in French-Canadian premenopausal women

Genes are important BMD determinants. We studied the association of an ESRRA gene functional variant with BMD in 1335 premenopausal women. The ESRRA genotype was an independent predictor of L2-L4 BMD, with an effect similar to smoking and equivalent to a 10-kg difference in weight.

INTRODUCTION

Several genetic polymorphisms have been associated with osteoporosis or osteoporosis fractures, but no functional effect has been shown for most of these gene variants. Because functional studies have implicated estrogen-related receptor alpha (ESRRA) in bone metabolism, we evaluated whether a recently described regulatory variant of the ESRRA gene is associated with lumbar and hip BMD as measured by DXA and with heel bone parameters as measured by quantitative ultrasound (QUS).

MATERIALS AND METHODS

Heel bone parameters were measured by right calcaneal QUS in 1335 healthy French-Canadian premenopausal women, and one-half of these women also had their BMD evaluated at two sites: femoral neck and lumbar spine (L2-L4) by DXA. All bone measures were tested separately for association with the ESRRA genotype by analysis of covariance. The significance of the ESRRA contribution to the model was also assessed by two different permutation tests.

RESULTS

A statistically significant association between ESRRA genotype and lumbar spine BMD was observed: women carrying the long ESRRA genotype had a 3.9% (0.045 g/cm2) higher lumbar spine BMD than those carrying the short ESRRA genotype (p = 0.004), independently of other risk factors measured. This effect of ESRRA genotype is similar to the effect of smoking and equivalent to a 10-kg difference in weight. This association was confirmed by permutation tests (p = 0.004). The same trend was observed for femoral neck BMD (2.6%, p = 0.07). However, no association was observed between ESRRA and QUS heel bone measures.

CONCLUSION

These results support the genetic influence of this ESRRA regulatory variant on BMD.

Lebanese guidelines for osteoporosis assessment and treatment: who to test? What measures to use? When to treat?

With the demographic explosion of the population worldwide, the human, social, and economic costs of osteoporosis will continue to rise. It is estimated that the magnitude of the problem might be even larger in developing countries, including those in the Middle East. Although several organizations and countries have developed or adapted guidelines to their local needs, as of today there are no guidelines for osteoporosis assessment in the Middle East. In April 2002, a panel of osteoporosis experts met and discussed practice guidelines for osteoporosis assessment and treatment in Lebanon. The process, which involved an overview of international guidelines as well as local data on osteoporosis, resulted in a draft for Lebanese guidelines that addressed three main questions: "Who to test?" "What measures to use?" and "When to treat?". Representatives from five major Lebanese societies (Endocrinology, Rheumatology, Orthopedics, Obstetrics and Gynecology, and Radiology) subsequently reviewed, discussed, and officially endorsed the guidelines after revisions. The Lebanese guidelines were also endorsed by the Eastern Mediterranean branch of the World Health Organization.

A second-stage genome scan for QTLs influencing BMD variation

Low bone mineral density (BMD) is a major risk factor for osteoporotic fracture. To identify genomic regions harboring quantitative trait loci (QTLs) contributing to BMD variation, we performed a two-stage genome screen. The first stage involved genotyping of a sample of 53 pedigrees with 630 individuals using 400 microsatellite markers spaced at approximately 10-cM intervals throughout the genome. Ten genomic regions with multi- and/or two-point LOD scores greater than 1.5 were observed. In the present second-stage study, 60 microsatellite markers, with a mean spacing of about 5 cM, were genotyped in these regions in an expanded sample of 79 pedigrees that contained 1816 subjects. Each pedigree was ascertained through a proband with extreme BMD at the hip or spine. BMD at the spine (L1-4), hip (the femoral neck, trochanter, and intertrochanteric region), and wrist (the ultradistal region) was measured by dual-energy X-ray absorptiometry (DXA) and was adjusted for age, sex, height, and weight. Two-point and multipoint linkage analyses were performed for each BMD site using statistical genetic methods that are implemented in the computer package SOLAR. Several regions (7q11, 10q26, 12q13, and 12q24) achieved LOD scores in excess of 1 in the second-stage followup study. The current results replicate some of our previous linkage findings and also highlight some of the difficulties facing microsatellite linkage mapping for complex human diseases.

Bone quantitative ultrasound and nutritional status in severely handicapped institutionalized children and adolescents

BACKGROUND & AIMS

Children with cerebral palsy (CP) have a high prevalence of pathologic fractures. Bone quantitative ultrasonography (QUS) has emerged as a radiation-free method for the assessment of bone quality and fracture risk. In this study, we applied QUS technique in order to investigate bone status in handicapped institutionalized children and adolescents.

METHODS

This cross-sectional study included 87 handicapped institutionalized patients. Measurements of the velocity of ultrasound wave, speed of sound (SOS), at distal radius and midshaft tibia, were performed using Omnisense 7000S analyser (Sunlight Ltd., Tel Aviv, Israel). In addition, all the participants had a thorough evaluation of nutritional status, demographic and clinical characteristics.

RESULTS

Forty-five of patients had either radius or tibia bone SOS lower than -1 SD, and 21% had either radius or tibia bone SOS lower than -2.5 SD. Using step-wise regression analysis, female gender (P=0.003) and stature (P=0.008) were correlated with radius SOS. Age (P=0.03) and fracture history (P=0.04) were negatively correlated with tibia SOS.

CONCLUSION

In this group of children and adolescents with CP one-fifth had poor bone status as suggested by low tibia/radius SOS assessed by QUS. Female gender, stature, age and fracture history were significantly correlated with poor bone status.

A whole-genome linkage scan suggests several genomic regions potentially containing quantitative trait Loci for osteoporosis

Osteoporosis is an important health problem, particularly in the elderly women. Bone mineral density (BMD) is a major determinant of osteoporosis. For a sample of 53 pedigrees that contain 1249 sibling pairs, 1098 grandparent-grandchildren pairs, and 2589 first cousin pairs, we performed a whole- genome linkage scan using 380 microsatellite markers to identify genomic regions that may contain quantitative trait loci (QTL) of BMD. Each pedigree was ascertained through a proband with BMD values belonging to the bottom 10% of the population. We conducted two-point and multipoint linkage analyses. Several potentially important genomic regions were suggested. For example, the genomic region near the marker D10S1651 may contain a QTL for hip BMD variation (with two-point analysis LOD score of 1.97 and multipoint analysis LOD score of 2.29). The genomic regions near the markers D4S413 and D12S1723 may contain QTLs for spine BMD variation (with two-point analysis LOD score of 2.12 and 2.17 and multipoint analysis LOD score of 3.08 and 2.96, respectively). The genomic regions identified in this and some earlier reports are compared for exploration in extension studies with larger samples and/or denser markers for confirmation and fine mapping to eventually identify major functional genes involved in osteoporosis.

Tests of linkage and/or association of genes for vitamin D receptor, osteocalcin, and parathyroid hormone with bone mineral density

Bone mineral density (BMD) is a major determinant of osteoporotic fractures (OFs). The heritability of BMD ranges from 50% to 90% in human populations. Extensive molecular genetic analyses have been performed through traditional linkage or association approaches to test and identify genes or genomic regions underlying BMD variation. The results, particularly those concerning the vitamin D receptor (VDR) gene, have been inconsistent and controversial. In this study, we simultaneously test linkage and/or association of the genes for VDR, osteocalcin (also known as bone Gla protein [BGP]), and parathyroid hormone (PTH) with BMD in 630 subjects from 53 human pedigrees. Each of these pedigrees was ascertained through a proband with an extreme BMD value at the hip or spine (Z score < or = -1.28). For the raw BMD values, adjusting for significant covariate effects of age, sex, and weight, we performed tests for linkage alone, association alone, and then both linkage and association. For the spine BMD, at the two markers (ApaI and FokI) inside the VDR gene we found evidence for linkage (p < 0.05) and for both linkage and association by the transmission disequilibrium test (TDT; p < 0.05); association was detected (p < 0.07) with regular statistical testing by analyses of variance (ANOVA). In addition, significant results were found for association alone (p < 0.05), linkage alone (p = 0.0005), and for linkage and association (p = 0.0019) for the intragenic marker HindIII of the BGP gene for the hip BMD. Through testing for association, linkage, and linkage and association simultaneously, our data support the VDR gene as a quantitative trait locus (QTL) underlying spine BMD variation and the BGP gene as a QTL underlying hip BMD variation. However, our data do not support the PTH gene as a QTL underlying hip or spine BMD variation. This is the first study in the broad field of bone genetics that tests candidate genes as QTLs for BMD by testing simultaneously for association alone, for linkage alone, and for association and linkage (via the TDT).

Role of genetics in osteoporosis

Osteoporosis is a disease characterized by fragile bones and high susceptibility to low-trauma fractures. It is a serious health problem, especially in elderly women. Bone mineral density (BMD) has been employed most commonly as the index for defining and studying osteoporosis. BMD has high genetic determination, with heritability ranging from 50 to 90%. Various gene-mapping approaches have been applied to identify specific genes underlying osteoporosis, largely using BMD as the study phenotype. We review here the genetic determination of osteoporosis as defined by BMD and discuss a fundamental issue we encounter in genetic research in osteoporosis: the choice of phenotype(s) to study. We briefly summarize and discuss advantages and disadvantages of various approaches used in genetic studies of osteoporosis. Finally, we review and discuss the current status for mapping and identification of genes for osteoporosis. We focus on linkage studies in humans and quantitative trait loci mapping in mice to supplement the already extensive reviews of association studies made by many investigators for candidate genes.

Relevance of the genes for bone mass variation to susceptibility to osteoporotic fractures and its implications to gene search for complex human diseases

We investigate the relevance of the genetic determination of bone mineral density (BMD) variation to that of differential risk to osteoporotic fractures (OF). The high heritability (h(2)) of BMD and the significant phenotypic correlations between high BMD and low risk to OF are well known. Little is reported on h(2) for OF. Extensive molecular genetic studies aimed at uncovering genes for differential risks to OF have focussed on BMD as a surrogate phenotype. However, the relevance of the genetic determination of BMD to that of OF is unknown. This relevance can be characterized by genetic correlation between BMD and OF. For 50 Caucasian pedigrees, we estimated that h(2) at the hip is 0.65 (P < 0.0001) for BMD and 0.53 (P < 0.05) for OF; however, the genetic correlation between BMD and OF is nonsignificant (P > 0.45) and less than 1% of additive genetic variance is shared between them. Hence, most genes found important for BMD may not be relevant to OF at the hip. The phenotypic correlation between high BMD and low risk to OF at the hip (approximately -0.30) is largely due to an environmental correlation (rho(E) = -0.73, P < 0.0001). The search for genes for OF should start with a significant h(2) for OF and should include risk factors (besides BMD) that are genetically correlated with OF. All genes found important for various risk factors must be tested for their relevance to OF. Ideally, employing OF per se as a direct phenotype for gene hunting and testing can ensure the importance and direct relevance of the genes found for the risk of OF. This study may have significant implications for the common practice of gene search for complex diseases through underlying risk factors (usually quantitative traits).

North American male reference population for speed of sound in bone at multiple skeletal sites

Alternatives to dual-energy X-ray absorptiometry (DXA) have been sought to increase access to low-cost osteoporosis risk assessment. Early quantitative ultrasound (QUS) systems measured speed of sound (SOS) and broadband ultrasound attenuation (BUA) at the calcaneus, and these were demonstrated to be good predictors of hip fracture risk. Recent studies have demonstrated the usefulness of other peripheral sites to assess bone status. The Sunlight Omnisense (Sunlight Medical, Rehovot, Israel) is a portable, inexpensive QUS device capable of multiple-site SOS measurement. To provide a robust male reference database, 588 healthy Caucasian males aged 20-90 yr were recruited from 6 centers across North America. SOS measurements were taken at the distal 1/3 radius, proximal third phalanx, midshaft tibia, and fifth metatarsal. A female reference database has previously been collected at North American sites. The results indicate that SOS in males exhibits an age-related decline beginning in the fifth decade at the radius, phalanx, and metatarsal, whereas the tibial SOS remains nearly constant until the ninth decade. Although females reach a higher-peak SOS than males at most sites, SOS is higher in males at all sites after the sixth decade, as a result of a more gradual decline in SOS. Longitudinal monitoring of healthy men should be performed to confirm these cross-sectional results.

A study on the influence of calcified intervertebral disk and aorta in determining bone mineral density

This study utilized dual-energy X-ray absorptiometry (DXA) to determine the association that age-related calcinosis of the aorta and intervertebral disks have in determining bone mineral density (BMD). Eight cadavers were chosen at random and were scanned with DXA before and after the removal of the aorta and intervertebral disks. Our results showed that the removal of sclerotic aortas decreased the vertebral BMD an average of 4.64% and the removal of two lumbar intervertebral disks further decreased BMD an average of 11.93%. These results were deemed significant at the 0.01 level using a Friedman two-way analysis of variance by ranks. It can be concluded that the presence of aortic arteriosclerotic lesions and intervertebral disk chondrocalcinosis add a significant contribution to BMD.

A national random survey of bone mineral density reporting in the United States

The rapidly evolving technology of bone mineral density (BMD) testing has revolutionized the clinical care of osteoporosis; however, at present, there are no guidelines for BMD reporting. A survey was mailed to a random sample of bone densitometry centers in the United States registered in the National Osteoporosis Foundation database in order to evaluate the practice of BMD reporting in the United States. Of the 1200 questionnaires mailed, 22.5% were completed and returned. Spine and hip BMD were routinely measured at 71% of the centers and were expressed as T-scores by 90% of centers. The World Health Organization working group definition of osteoporosis was included in the report by 64% of the survey responders and was used as the sole criterion to make treatment recommendations by 34%. Fracture risk was reported by 70% of the centers and only the minority (<15%) applied appropriate age and gender restrictions. There were geographic and specialty variations in the practices of bone density reporting. Despite the established value of clinical densitometry in the care of patients at risk for osteoporosis, our survey revealed that clinical information, including fracture risk, was missing from many reports. A re-examination of the practice of clinical densitometry reporting is warranted.

Assessment of bone status using speed of sound at multiple anatomical sites

Studies in vitro and in vivo have shown that quantitative ultrasound (QUS) is a valid tool for the assessment of bone status. Current QUS methods using the transmission technique are limited to one peripheral bone site. A new system, Sunlight Omnisense (Omnisense, Sunlight Medical Ltd., Rehovot, Israel), measures speed of sound (SOS, in m/s) along the surface of the bone based on an axial transmission technique. The Omnisense can measure SOS at several anatomical sites. This study evaluated the SOS at different anatomical sites in a healthy population. A total of 334 adult women from three research centers in the USA and Canada with a mean (+/- SD) age of 48.8 (+/- 17.4) years were enrolled in this study. SOS was measured at the proximal third phalanx, distal one third radius, midshaft tibia, and fifth metatarsal. The mean SOS (+/- SD) values for the phalanx, radius, tibia and metatarsal were 3984 (+/- 221), 4087 (+/- 147), 3893 (+/- 150) and 3690 (+/- 246) m/s, respectively. Each anatomical site SOS was significantly different (p < 0.001) from that of the other sites. SOS at the different anatomical sites was modestly, but significantly, correlated (r = 0.31 to 0.56, p < 0.001). Similar correlation coefficients were obtained for the T scores. The mean T scores for subjects over the age of 60 years were -1.94, -2.01, -0.97 and -1.42 for the phalanx, radius, tibia and metatarsal, respectively. The age of peak SOS and the rate of change thereafter varied with anatomical site, implying that the prevalence of osteopenia and osteoporosis was site-dependent if only one T score cut-off point was used. Comparing individuals, 10% to 17% of patients had T scores that differed by more than a factor of 2 between sites. Weight and age were some of the contributing factors to this heterogeneity. The Omnisense provides an opportunity to assess bone status at different anatomical sites. Whether or not combining measurements from all these anatomical sites will improve osteoporosis management still needs to be determined.

Toward high-throughput genotyping: dynamic and automatic software for manipulating large-scale genotype data using fluorescently labeled dinucleotide markers

To efficiently manipulate large amounts of genotype data generated with fluorescently labeled dinucleotide markers, we developed a Microsoft database management system, named. offers several advantages. First, it accommodates the dynamic nature of the accumulations of genotype data during the genotyping process; some data need to be confirmed or replaced by repeat lab procedures. By using, the raw genotype data can be imported easily and continuously and incorporated into the database during the genotyping process that may continue over an extended period of time in large projects. Second, almost all of the procedures are automatic, including autocomparison of the raw data read by different technicians from the same gel, autoadjustment among the allele fragment-size data from cross-runs or cross-platforms, autobinning of alleles, and autocompilation of genotype data for suitable programs to perform inheritance check in pedigrees. Third, provides functions to track electrophoresis gel files to locate gel or sample sources for any resultant genotype data, which is extremely helpful for double-checking consistency of raw and final data and for directing repeat experiments. In addition, the user-friendly graphic interface of renders processing of large amounts of data much less labor-intensive. Furthermore, has built-in mechanisms to detect some genotyping errors and to assess the quality of genotype data that then are summarized in the statistic reports automatically generated by. The can easily handle >500,000 genotype data entries, a number more than sufficient for typical whole-genome linkage studies. The modules and programs we developed for the can be extended to other database platforms, such as Microsoft SQL server, if the capability to handle still greater quantities of genotype data simultaneously is desired.

Diagnostic discrepancies between two closely related forearm bone density measurement sites

At the present time the diagnosis of osteoporosis is based on the use of T-scores. Measurements at different skeletal sites or of different regions of interest may result in diagnostic discrepancies. In this study, we tried to demonstrate that bone mineral density (BMD)values at the closely related forearm sites may lead to diagnostic uncertainty, and to assess the degree of site heterogeneity across different age groups. The study consisted of 2348 women (age 20-83) referred for bone densitometry. Forearm BMD was measured at the distal and ultradistal sites by single X-ray absorptiometry (DTX-100 device). T-scores were calculated from Bulgarian reference data. Diagnostic disagreement between sites was found in 19.3% of all women. In 7.7% of all cases, the difference between T-scores at the two sites exceeded 1. The discrepancies were more pronounced after age 60. This corresponds well to the different onset and rates of trabecular and cortical bone losses as well as to their different distribution along the forearm. We encourage the separate assessment of cortical and trabecular bone densities or measurements at axial sites in case forearm sites yield conflicting results or low-normal BMD values.

Multisite bone ultrasound measurement on North American female reference population

The Sunlight Omnisense is a portable quantitative ultrasound device that measures speed of sound (SOS) at multiple skeletal sites and therefore has the potential to provide a more complete assessment of an individual's overall fracture risk than single-site measurements such as the calcaneus. To provide a robust normative female database, 545 healthy Caucasian women ages 20-90 were recruited at five centers across North America. SOS measurements were obtained from the distal one-third radius, proximal third phalanx, midshaft tibia, and fifth metatarsal. The results demonstrate that peak SOS occurs around the age of 40, with maximum mean values of 4161, 3928, 3786, and 4092 m/s seen at the radius, tibia, metatarsal, and phalanx, respectively. Maximal rate of decline of SOS was seen in the decade following menopause (-12.4, -9.2, -12.1, and -18.8 m/s at the radius, tibia, metatarsal, and phalanx, respectively). Reproducibility between successive measurements indicates high precision, with standardized coefficients of variance ranging between 1.5 and 4.5%. Greatest precision was seen at the metatarsal. Further work is required to clarify the biologic significance of multisite SOS measurements and their use in the assessment of fracture risk.

Determination of bone mineral density of the hip and spine in human pedigrees by genetic and life-style factors

In 40 human pedigrees with 563 subjects, we evaluated the contribution of genetic and life-style factors (exercise, smoking, and alcohol consumption) and the interactions between non-genetic factors in determining bone mineral density (BMD) of the hip and spine. In our analysis, we adjusted for age, weight, height, menopausal status in females, life-style factors, and the significant interactions among these factors. For the spine and hip BMD, heritabilities (h(2)) (+/- SE) were, respectively, 0.68 (0.21) and 0.86 (0.28) in males and 0.64 (0.13) and 0.67 (0.14) in females. Exercise had significant beneficial effects for male spine BMD and female hip BMD. Alcohol consumption experienced in our sample had significant beneficial effects on hip BMD in both sexes. Although the main effect of smoking was not significant, there were significant interaction effects between smoking and other important factors (e.g., exercise, weight, alcohol consumption). For example, for female spine BMD, exercise had significant beneficial effects in smokers; however, its effect in non-smokers was non-significant. This result indicates that exercise may reduce deleterious effects of smoking (if any) on BMD, but may have minor effects in increasing BMD in non-smokers. The various interaction effects among risk factors explicitly revealed here for the first time indicate that the detailed effects and direction of individual risk factors may depend on the presence and magnitude of other factors. Weight invariably affected BMD of the hip and spine in both sexes. Age effects were significant for hip BMD, but not for male spine BMD.

Effect of estrogen replacement therapy on speed of sound at multiple skeletal sites

OBJECTIVES

To evaluate the effect of estrogen replacement therapy (ERT) on postmenopausal bone loss by multi-site ultrasound measurement.

METHODS

A cross-sectional comparison of postmenopausal women, ERT users and non-users. The two study groups were enrolled for the reference database collection for the Sunlight Omnisense (Omnisense) and were matched by years since menopause. Speed of sound (SOS) was measured at the distal radius (RAD), mid-shaft tibia (TIB), fifth metatarsus (MTR) and proximal phalanx (PLX).

RESULTS

143 ERT users for 5.2+/-3.6 years were compared with 139 ERT non-users (age: 57.0+/-5.3 and 57.5+/-5.5, respectively). Both groups were 7.1+/-5.0 years since menopause. SOS, expressed in T-score units, was higher at the RAD in ERT users as compared to ERT non-users (-0.55+/-1.30 and -1.36+/-1.60, respectively, P<0.0001), and at the TIB (-0.73+/-1.34 and -1.28+/-1.45, respectively, P=0. 003). Same trend was observed at the MTR and PLX, but not statistically significant because of fewer observations. In early post menopause period, the ERT-non users RAD data shows an annual SOS decrease of 0.17 versus annual increase of 0.12 T-score units (P=0.037). Similar effect is observed at the TIB, though not statistically significant (non-users decrease of 0.20 vs. users increase of 0.08 T-score units/year, P=0.086).

CONCLUSIONS

SOS measurements by Omnisense at multiple skeletal sites support the ERT protective effect on bone.

A fracture risk profile using single-site bone density assessment and clinical risk factors

The Risk Factor Profile combines single-site bone density assessment and selected clinical risk factors to help estimate the risk of osteoporotic fracture for Caucasian postmenopausal women over the next 5 years. The bone density assessment uses T score cut-off values equivalent to the WHO definitions of osteoporosis and osteopenia at the hip that would identify 16-17% of women over 50 years of age as "high" risk. The clinical risk factors are defined as "major" producing about a doubling of fracture risk independent of bone density, and "minor" where the predictive power is less certain. The indications for a risk factor assessment using the Profile are the same as for any bone density assessment with the exception of monitoring response to treatment. In practice the clinical risk factors can be measured at the time of the bone density estimation taking only a few minutes. The decision to treat, or not to treat, a postmenopausal woman at high or medium risk will ultimately depend on the overall assessment of risks and benefits, costs of treatment and the desires of the patient. The Risk Factor Profile aims to supply the clinician with a simple tool to aid treatment decision-making.

Genetic determination of variation and covariation of peak bone mass at the hip and spine

The likelihood of low trauma fracture in the elderly is highly predictable by peak bone mass (PBM) at age approximately 25-50 yr. We estimated the magnitude of genetic determination of the variation and covariation of PBM of the spine and hip (adjusted by age, gender, and ethnicity) in 47 independent healthy full-sib pairs and 27 healthy mother-offspring pairs. For the spine and hip, the narrow-sense heritabilities (h(2)) (mean +/- SE) were 0.76 +/- 0.34 and 0.84 +/- 0.36, respectively, when estimated from full sibs, and 0.86 +/- 0.38 and 0.84 +/- 0.39, respectively, when estimated from parent-offspring. Some genetic loci underlying PBM variation at the hip and spine are the same or closely linked, as is reflected by the high genetic correlation of 0.95 +/- 0.05 between them when estimated from full sibs, and 0.57 +/- 0.27 when estimated from parent-offspring, respectively. Generally, common familial environmental effects shared by relatives may bias these estimates. However, these effects may be small, since our results reported herein and those in other earlier studies indicate that common familial environmental effects are probably negligible in causing similarity of bone mass among family members. The correlation of bone mass among randomly sampled couples living in the same household is small and nonsignificant as measured either by densitometry at the radius and ulna or by quantitative ultrasound at the patella. The problem of shared environmental effects notwithstanding, we conclude that much of the PBM variation and covariation at the hip and spine is determined genetically.