Genetic influence on bone turnover in postmenopausal twins

[18F] Sodium Fluoride PET Kinetic Parameters in Bone Imaging

This report describes the significance of the kinetic parameters (k-values) obtained from the analysis of dynamic positron emission tomography (PET) scans using the Hawkins model describing the pharmacokinetics of sodium fluoride ([¹⁸F]NaF) to understand bone physiology. Dynamic [¹⁸F]NaF PET scans may be useful as an imaging biomarker in early phase clinical trials of novel drugs in development by permitting early detection of treatment-response signals that may help avoid late-stage attrition.

Disentangling the relationship between bone turnover and glucose homeostasis: A prospective, population-based twin study

Background

Biochemical markers of bone turnover are lower in patients with type 2 diabetes, which may be explained by genetic variants being associated with type 2 diabetes and bone turnover as well as environmental factors. We hypothesized that bone turnover markers associate with and predict changes in glucose homeostasis after control for genetics and shared environment.

Methods

1071 healthy, non-diabetic (at baseline, 1997-2000) adult mono- and dizygotic twins participating in the prospective study GEMINAKAR were reassessed between 2010 and 2012 with clinical evaluation, biochemical tests and oral glucose tolerance test. Fasting bone turnover markers (CTX, P1NP and osteocalcin) were measured. The association between bone turnover, glucose homeostasis and the ability of bone turnover markers to predict changes in glucose homeostasis were assessed in cross-sectional and longitudinal analyses. Analyses were performed both at an individual level and adjusted for shared environmental and genetic factors.

Results

Glucose levels increased with age, and 33 (3%) participants had developed type 2 diabetes at follow-up. In women, bone turnover markers increased with age, whereas for men only osteocalcin increased with age. Bone turnover markers were not associated with fasting glucose, insulin, or HOMA-IR at baseline or follow-up before or after adjustment for age, sex, BMI, smoking, and use of medication at baseline. Variation in bone turnover markers was mainly explained by unique environmental factors, 70%, 70% and 55% for CTX, P1NP and osteocalcin, respectively, whereas additive genetic factors explained 7%, 13% and 45% of the variation in CTX, P1NP and osteocalcin.

Conclusions

Bone turnover markers were not associated with baseline plasma glucose levels and did not predict changes in glucose homeostasis. Variation in bone turnover markers is mainly explained by environmental factors, however, compared to CTX and P1NP, genetic factors have a larger impact on osteocalcin levels.

Trabecular architecture of the great ape and human femoral head

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole-epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle-walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.

Trabecular bone patterning in the hominoid distal femur

BACKGROUND

In addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.

METHODS

Micro-computed tomography scans of Homo sapiens (n = 11), Pan troglodytes (n = 18), Gorilla gorilla (n = 14) and Pongo sp. (n = 7) were used to investigate trabecular structure throughout the distal epiphysis of the femur. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles in Homo would be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion.

RESULTS

Results indicate some significant differences between taxa, with the most prominent being higher BV/TV in the posterosuperior region of the condyles in Pan and higher BV/TV and anisotropy in the posteroinferior region in Homo. Furthermore, trabecular number, spacing and thickness differ significantly, mainly separating Gorilla from the other apes.

DISCUSSION

The trabecular architecture of the distal femur holds a functional signal linked to habitual behaviour; however, there was more similarity across taxa and greater intraspecific variability than expected. Specifically, there was a large degree of overlap in trabecular structure across the sample, and Homo was not as distinct as predicted. Nonetheless, this study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa.

The clinical contribution of cortical porosity to fragility fractures

Cortical bone is not compact; rather it is penetrated by many Haversian and Volkmann canals for blood supply. The lining of these canals are the intracortical bone surfaces available for bone remodeling. Increasing intracortical bone remodeling increases cortical porosity. However, cortical bone loss occurs more slowly than trabecular loss due to the fact that less surface per unit of bone matrix volume is available for bone remodeling. Nevertheless, most of the bone loss over time is cortical because cortical bone constitutes 80% of the skeleton, and the relative proportion of trabecular bone diminishes with advancing age. Higher serum levels of bone turnover markers are associated with higher cortical porosity of the distal tibia and the proximal femur. Greater porosity of the distal radius is associated with higher odds for forearm fracture, and greater porosity of the proximal femur is associated with higher odds for non-vertebral fracture in postmenopausal women. Measurement of cortical porosity contributes to fracture risk independent of areal bone mineral density and Fracture Risk Assessment Tool. On the other hand, antiresorptive treatment reduces porosity at the distal radius and at the proximal femoral shaft. Thus, porosity is a substantial determinant of the bone fragility that underlies the risk of fractures and may be a target for fracture prevention.

Premenopausal Trabecular Bone Loss is Associated with a Family History of Fragility Fracture

INTRODUCTION

Although a fragility fracture family history (FFFH+) has repeatedly been shown to be associated with lower bone mineral density (BMD), its relationship to human BMD change is unclear. Animal research, however, documented that different purebred strains within rodent species have wide ranges in rates of bone acquisition during growth as well as in change post-ovariectomy. Our objective was to compare the rate of premenopausal spinal trabecular BMD change between women with and without a general family history of fragility fracture.

PARTICIPANTS AND METHODS

Healthy premenopausal community women participated in prospective observational studies at two academic medical research centres: Vancouver, Canada (n = 66) and Munich, Germany (n = 20). The primary outcome was annual spinal BMD change, measured by quantitative computed tomography (QCT). The two studies employed similar methodologies for assessing QCT and FFFH.

RESULTS

Volunteer community participants had a mean age of 36.0 (SD, 6.9) years, body mass index 22.5 (2.4) and baseline QCT of 150.2 (22.5) mg/cm³ trabecular bone. The rates of BMD change were similar in both cities: - 3.5 (5.1)/year Vancouver, - 2.0 (3.4)/year Munich (95 % CI of difference: - 3.9, 0.9). Over a third of the women (31 of the 86, 36 %) reported FFFH+. Those with and without a FFFH were similar in demographics, nutrition, exercise, menstrual cycle and luteal phase lengths and physiological measures (serum calcium, osteocalcin and estradiol). However, women with FFFH+ lost trabecular BMD more rapidly: FFFH+, - 4.9 (5.0), FFFH-, - 2.2 (4.4) mg/cm³/year (95 % CI diff - 0.7 to - 4.8, F_1.83 = 7.88, p = 0.006). FFFH+ explained 7.7 % of the variance in QCT volumetric trabecular spinal bone change/year in these healthy premenopausal women.

CONCLUSION

This study shows for the first time that having a history of a fragility fracture in a family member is associated with a greater rate of premenopausal spinal trabecular bone loss.

Fine mapping of bone structure and strength QTLs in heterogeneous stock rat

We previously demonstrated that skeletal structure and strength phenotypes vary considerably in heterogeneous stock (HS) rats. These phenotypes were found to be strongly heritable, suggesting that the HS rat model represents a unique genetic resource for dissecting the complex genetic etiology underlying bone fragility. The purpose of this study was to identify and localize genes associated with bone structure and strength phenotypes using 1524 adult male and female HS rats between 17 to 20 weeks of age. Structure measures included femur length, neck width, head width; femur and lumbar spine (L3-5) areas obtained by DXA; and cross-sectional areas (CSA) at the midshaft, distal femur and femoral neck, and the 5th lumbar vertebra measured by CT. In addition, measures of strength of the whole femur and femoral neck were obtained. Approximately 70,000 polymorphic SNPs distributed throughout the rat genome were selected for genotyping, with a mean linkage disequilibrium coefficient between neighboring SNPs of 0.95. Haplotypes were estimated across the entire genome for each rat using a multipoint haplotype reconstruction method, which calculates the probability of descent at each locus from each of the 8 HS founder strains. The haplotypes were then tested for association with each structure and strength phenotype via a mixed model with covariate adjustment. We identified quantitative trait loci (QTLs) for structure phenotypes on chromosomes 3, 8, 10, 12, 17 and 20, and QTLs for strength phenotypes on chromosomes 5, 10 and 11 that met a conservative genome-wide empiric significance threshold (FDR=5%; P<3×10(-6)). Importantly, most QTLs were localized to very narrow genomic regions (as small as 0.3 Mb and up to 3 Mb), each harboring a small set of candidate genes, both novel and previously shown to have roles in skeletal development and homeostasis.

High-resolution genome screen for bone mineral density in heterogeneous stock rat

We previously demonstrated that skeletal mass, structure, and biomechanical properties vary considerably in heterogeneous stock (HS) rat strains. In addition, we observed strong heritability for several of these skeletal phenotypes in the HS rat model, suggesting that it represents a unique genetic resource for dissecting the complex genetics underlying bone fragility. The purpose of this study was to identify and localize genes associated with bone mineral density in HS rats. We measured bone phenotypes from 1524 adult male and female HS rats between 17 and 20 weeks of age. Phenotypes included dual-energy X-ray absorptiometry (DXA) measurements for bone mineral content and areal bone mineral density (aBMD) for femur and lumbar spine (L3-L5), and volumetric BMD measurements by CT for the midshaft and distal femur, femur neck, and fifth lumbar vertebra (L5). A total of 70,000 polymorphic single-nucleotide polymorphisms (SNPs) distributed throughout the genome were selected from genotypes obtained from the Affymetrix rat custom SNPs array for the HS rat population. These SNPs spanned the HS rat genome with a mean linkage disequilibrium coefficient between neighboring SNPs of 0.95. Haplotypes were estimated across the entire genome for each rat using a multipoint haplotype reconstruction method, which calculates the probability of descent for each genotyped locus from each of the eight founder HS strains. The haplotypes were tested for association with each bone density phenotype via a mixed model with covariate adjustment. We identified quantitative trait loci (QTLs) for BMD phenotypes on chromosomes 2, 9, 10, and 13 meeting a conservative genomewide empiric significance threshold (false discovery rate [FDR] = 5%; p < 3 × 10(-6)). Importantly, most QTLs were localized to very small genomic regions (1-3 megabases [Mb]), allowing us to identify a narrow set of potential candidate genes including both novel genes and genes previously shown to have roles in skeletal development and homeostasis.

Genetic influence on bone phenotypes and body composition: a Swedish twin study

Bone mineral density (BMD), bone size and bone turnover are independent determinants of fractures in elderly. Earlier twin studies of these phenotypes have revealed high heritability for BMD and bone area, and more moderate heritability for bone turnover markers. No previous Scandinavian study has evaluated the genetic and environmental contribution to the variance of these phenotypes, despite the fact that Scandinavian countries have the highest incidence of osteoporotic fractures worldwide. Participants were selected from the Swedish Twin Registry. All intact like-sexed twin pairs born in 1965 or earlier and living in the county of Uppsala were invited to participate. A total of 102 twin pairs (45 monozygotic and 57 dizygotic) accepted the invitation to participate. All twins underwent measurement of BMD and bone area using dual-energy X-ray absorptiometry. Hip geometry was also calculated. Markers for bone formation (osteocalcin) and bone resorption (CrossLaps) were measured in serum. We observed a substantial heritability for BMD at the lumbar spine (0.85; 95 % CI 0.54-0.90), the femoral neck (0.75; 95 % CI 0.62-0.83), and the proximal femur (0.84; 95 % CI 0.74-0.90). The values for bone area were approximately similar to those for BMD. Bone turnover markers had a slightly lower genetic influence with a value of 0.69 (0.53-0.80) for osteocalcin and 0.58 (95 % CI 0.33-0.75) for CrossLaps. As a comparison, the heritabilities of body height and weight were 0.95 and 0.82, respectively. The high heritability on bone phenotypes among Swedish middle-aged and older men and women should encourage further work on the identification of specific genetic pathways. Continuing research in this area could reveal the mechanisms behind the strong genetic susceptibility of bone-related phenotypes.

Vitamin D receptor gene polymorphisms and bone mass indices in post-menarchal Indian adolescent girls

To study the association between vitamin D receptor (VDR) gene polymorphisms and bone mass indices in adolescent girls, a cross-sectional study was conducted in 120 post-menarchal girls aged 15-18 years in Pune city, India. Serum levels of ionised calcium, inorganic phosphorous, parathyroid hormone and 25-hydroxy vitamin-D were measured. Bone mineral content (BMC), bone area (BA) and bone mineral density (BMD) were measured at total body (TB), lumbar spine (LS) and left femoral neck (FN) using dual energy X-ray absorptiometry. Polymorphisms of the VDR gene at the Fok1 and Bsm1 loci were detected using SYBR Green quantitative polymerase chain reaction. The overall distribution of genotypes at the Bsm1 locus in this study was 33.3 % Bb, 29.2 % bb and 37.5 % BB while that for the Fok1 locus was 44.2 % Ff, 7.5 % ff and 48.3 % FF. There were no significant differences in the blood parameters when classified according to Bsm1 or Fok1 genotypes. Subjects with BB genotype have significantly higher mean TBBMC, TBBA, TBBMD and LSBMD than Bb and bb (p < 0.05) and showed a tendency for association with LSBMC and LSBA (p < 0.1). Subjects with Ff genotype showed a tendency for association with left FNBMC and FNBA (p < 0.1). Bsm1 genotype did not show an association with FN bone indices whereas Fok1 genotype did not show association with TB or LS bone indices. In conclusion, the present study demonstrates VDR gene polymorphism, defined by Bsm1 genotype, has an influence on total body and lumbar spine bone mass indices in post-menarchal Indian girls.

Genetic analysis of serum osteocalcin and bone mineral in multigenerational Afro-Caribbean families

Osteocalcin is a major component of bone matrix. Concentrations of total, carboxylated, and uncarboxylated osteocalcin, are highly heritable and genetically correlated with bone mineral content (BMC) within African ancestry families.

INTRODUCTION

Osteocalcin (OC) is a protein constituent of bone matrix and a marker of bone formation. We characterized the heritability of serum OC measures and identified genomic regions potentially involved in the regulation of OC via high-density genome-wide linkage analysis in African ancestry individuals.

METHODS

African ancestry individuals (n = 459) were recruited, without regard to health status, from seven probands (mean family size = 66; 4,373 relative pairs). Residual heritability of serum OC measures was estimated and multipoint quantitative trait linkage analysis was performed using pedigree-based maximum likelihood methods.

RESULTS

Residual heritabilities of total OC, uncarboxylated OC, carboxylated OC and percent uncarboxylated OC were 0.74 ± 0.10, 0.89 ± 0.08, 0.46 ± 0.10 and 0.41 ± 0.09, respectively. All OC measures were genetically correlated with whole body BMC. We obtained strong evidence of bivariate linkage for percent uncarboxylated OC and whole body BMC on chromosome 17 (logarithm of the odds [LOD] = 3.15, 99 cM).

CONCLUSIONS

All forms of OC were highly heritable and genetically correlated with total body BMC in these African ancestry families. The identified linkage region contains several candidate genes for bone and energy metabolism including COL1A1 and TNFRSF11A. Further studies of this genomic region may reveal novel insight into the genetic regulation of OC and bone mineralization.

Heterogeneous stock rat: a unique animal model for mapping genes influencing bone fragility

Previously, we demonstrated that skeletal mass, structure and biomechanical properties vary considerably among 11 different inbred rat strains. Subsequently, we performed quantitative trait loci (QTL) analysis in four inbred rat strains (F344, LEW, COP and DA) for different bone phenotypes and identified several candidate genes influencing various bone traits. The standard approach to narrowing QTL intervals down to a few candidate genes typically employs the generation of congenic lines, which is time consuming and often not successful. A potential alternative approach is to use a highly genetically informative animal model resource capable of delivering very high resolution gene mapping such as Heterogeneous stock (HS) rat. HS rat was derived from eight inbred progenitors: ACI/N, BN/SsN, BUF/N, F344/N, M520/N, MR/N, WKY/N and WN/N. The genetic recombination pattern generated across 50 generations in these rats has been shown to deliver ultra-high even gene-level resolution for complex genetic studies. The purpose of this study is to investigate the usefulness of the HS rat model for fine mapping and identification of genes underlying bone fragility phenotypes. We compared bone geometry, density and strength phenotypes at multiple skeletal sites in HS rats with those obtained from five of the eight progenitor inbred strains. In addition, we estimated the heritability for different bone phenotypes in these rats and employed principal component analysis to explore relationships among bone phenotypes in the HS rats. Our study demonstrates that significant variability exists for different skeletal phenotypes in HS rats compared with their inbred progenitors. In addition, we estimated high heritability for several bone phenotypes and biologically interpretable factors explaining significant overall variability, suggesting that the HS rat model could be a unique genetic resource for rapid and efficient discovery of the genetic determinants of bone fragility.

Genetic determinants of osteoporosis: common bases to cardiovascular diseases?

Osteoporosis is the most common and serious age-related skeletal disorder, characterized by a low bone mass and bone microarchitectural deterioration, with a consequent increase in bone fragility and susceptibility to spontaneous fractures, and it represents a major worldwide health care problem with important implications for health care costs, morbidity and mortality. Today is well accepted that osteoporosis is a multifactorial disorder caused by the interaction between environment and genes that singularly exert modest effects on bone mass and other aspects of bone strength and fracture risk. The individuation of genetic factors responsible for osteoporosis predisposition and development is fundamental for the disease prevention and for the setting of novel therapies, before fracture occurrence. In the last decades the interest of the Scientific Community has been concentrated in the understanding the genetic bases of this disease but with controversial and/or inconclusive results. This review tries to summarize data on the most representative osteoporosis candidate genes. Moreover, since recently osteoporosis and cardiovascular diseases have shown to share common physiopathological mechanisms, this review also provides information on the current understanding of osteoporosis and cardiovascular diseases common genetic bases.

Genes influencing spinal bone mineral density in inbred F344, LEW, COP, and DA rats

Previously, we identified the regions of chromosomes 10q12-q31 and 15p16-q21 harbor quantitative trait loci (QTLs) for lumbar volumetric bone mineral density (vBMD) in female F2 rats derived from Fischer 344 (F344) x Lewis (LEW) and Copenhagen 2331 (COP) x Dark Agouti (DA) crosses. The purpose of this study is to identify the candidate genes within these QTL regions contributing to the variation in lumbar vBMD. RNA was extracted from bone tissue of F344, LEW, COP, and DA rats. Microarray analysis was performed using Affymetrix Rat Genome 230 2.0 Arrays. Genes differentially expressed among the rat strains were then ranked based on the strength of the correlation with lumbar vBMD in F2 animals derived from these rats. Quantitative PCR (qPCR) analysis was performed to confirm the prioritized candidate genes. A total of 285 genes were differentially expressed among all strains of rats with a false discovery rate less than 10%. Among these genes, 18 candidate genes were prioritized based on their strong correlation (r (2) > 0.90) with lumbar vBMD. Of these, 14 genes (Akap1, Asgr2, Esd, Fam101b, Irf1, Lcp1, Ltc4s, Mdp-1, Pdhb, Plxdc1, Rabep1, Rhot1, Slc2a4, Xpo4) were confirmed by qPCR. We identified several novel candidate genes influencing spinal vBMD in rats.

Differentially expressed genes strongly correlated with femur strength in rats

The region of chromosome 1q33-q54 harbors quantitative trait loci (QTL) for femur strength in COPxDA and F344xLEW F2 rats. The purpose of this study is to identify the genes within this QTL region that contribute to the variation in femur strength. Microarray analysis was performed using RNA extracted from femurs of COP, DA, F344 and LEW rats. Genes differentially expressed in the 1q33-q54 region among these rat strains were then ranked based on the strength of correlation with femur strength in F2 animals derived from these rats. A total of 214 genes in this QTL region were differentially expressed among all rat strains, and 81 genes were found to be strongly correlated (r(2)>0.50) with femur strength. Of these, 12 candidate genes were prioritized for further validation, and 8 of these genes (Ifit3, Ppp2r5b, Irf7, Mpeg1, Bloc1s2, Pycard, Sec23ip, and Hps6) were confirmed by quantitative PCR (qPCR). Ingenuity Pathway Analysis suggested that these genes were involved in interferon alpha, nuclear factor-kappa B (NFkB), extracellular signal-related kinase (ERK), hepatocyte nuclear factor 4 alpha (HNF4A) and tumor necrosis factor (TNF) pathways.

Genomic expression analysis of rat chromosome 4 for skeletal traits at femoral neck

Hip fracture is the most devastating osteoporotic fracture type with significant morbidity and mortality. Several studies in humans and animal models identified chromosomal regions linked to hip size and bone mass. Previously, we identified that the region of 4q21-q41 on rat chromosome (Chr) 4 harbors multiple femoral neck quantitative trait loci (QTLs) in inbred Fischer 344 (F344) and Lewis (LEW) rats. The purpose of this study is to identify the candidate genes for femoral neck structure and density by correlating gene expression in the proximal femur with the femoral neck phenotypes linked to the QTLs on Chr 4. RNA was extracted from proximal femora of 4-wk-old rats from F344 and LEW strains, and two other strains, Copenhagen 2331 and Dark Agouti, were used as a negative control. Microarray analysis was performed using Affymetrix Rat Genome 230 2.0 arrays. A total of 99 genes in the 4q21-q41 region were differentially expressed (P < 0.05) among all strains of rats with a false discovery rate <10%. These 99 genes were then ranked based on the strength of correlation between femoral neck phenotypes measured in F2 animals, homozygous for a particular strain's allele at the Chr 4 QTL and the expression level of the gene in that strain. A total of 18 candidate genes were strongly correlated (r(2) > 0.50) with femoral neck width and prioritized for further analysis. Quantitative PCR analysis confirmed 14 of 18 of the candidate genes. Ingenuity pathway analysis revealed several direct or indirect relationships among the candidate genes related to angiogenesis (VEGF), bone growth (FGF2), bone formation (IGF2 and IGF2BP3), and resorption (TNF). This study provides a shortened list of genetic determinants of skeletal traits at the hip and may lead to novel approaches for prevention and treatment of hip fracture.

Osteoporosis, schizophrenia and antipsychotics: the need for a comprehensive multifactorial evaluation

Osteoporosis is recognised as a major public health issue leading to bone fractures, pain and disability. Awareness of an elevated risk of osteoporosis in individuals with schizophrenia is increasing. An accelerated decrease in bone mineral density (BMD) in patients with schizophrenia may be disease related or drug induced. A drug-induced decrease in BMD has been attributed mostly to hyperprolactinaemia and its consequences. However, as demonstrated in this review, decreased BMD and osteoporosis are multifactorial processes, and abnormal bone structure and functions are not limited to BMD. Multiple dynamic processes may lead to impairment of bone homeostasis and eventually to bone abnormalities. Many of these processes may be abnormal in treated as well as untreated patients with schizophrenia. Despite many publications, the epidemiology of abnormal bone structure, mineralisation and dynamics in patients with schizophrenia is still not fully determined. Comprehensive studies of bone dynamics in individuals with first-episode schizophrenia, as well as in patients treated with various current medications, are needed in order to characterise the problem(s) and then to develop relevant treatment and prevention strategies.

Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins

Supine weight-bearing exercise within lower body negative pressure (LBNP) alleviates some of the skeletal deconditioning induced by simulated weightlessness in men. We examined this potential beneficial effect in women. Because dietary acid load affected the degree of bone resorption in men during bed rest, we also investigated this variable in women. Subjects were 7 pairs of female identical twins assigned at random to 2 groups, sedentary bed rest (control) or bed rest with supine treadmill exercise within LBNP. Dietary intake was controlled and monitored. Urinary calcium and markers of bone resorption were measured before bed rest and on bed rest days 5/6, 12/13, 19/20, and 26/27. Bone mineral content was assessed by dual-energy X-ray absorptiometry before and after bed rest. Data were analyzed by repeated-measures two-way analysis of variance. Pearson correlation coefficients were used to define the relationships between diet and markers of bone metabolism and to estimate heritability of markers. During bed rest, all markers of bone resorption and urinary calcium and phosphorus increased (P<0.001); parathyroid hormone (P=0.06), bone-specific alkaline phosphatase (P=0.06), and 1,25-dihydroxyvitamin D (P=0.09) tended to decrease. LBNP exercise tended to mitigate bone density loss. The ratio of dietary animal protein to potassium was positively correlated with urinary calcium excretion for all weeks of bed rest in the control group, but only during weeks 1 and 3 in the exercise group. Pre-bed rest data suggested that many markers of bone metabolism have strong genetic determinants. Treadmill exercise within LBNP had less of a protective effect on bone resorption during bed rest in women than previously published results had shown for its effect in men, but the same trends were observed for both sexes. Dietary acid load of these female subjects was significantly correlated with calcium excretion but not with other bone resorption markers.

The effect of bilateral oophorectomy on bone mineral density

The objective of this study is to investigate the effect of bilateral oophorectomy with total abdominal hysterectomy on bone loss, comparing the cases having surgery before and after the menopause. Bone mineral density (BMD) measurements were obtained from the lumbar spine and femoral neck of totally 127 cases. Out of 127, 105 had surgery before menopause and 22 cases were operated on postmenopausally. The results were compared with the USA normal values. The average age of surgical menopause (SM) cases was 48.45 years with a mean duration of menopause of 5.77 years. The average height and weight were 157.67 cm and 68.19 kg, respectively. The average age of cases having surgery after menopause (SAM) was 62.45 years with a mean duration of 5.59 years after the surgery (duration after menopause is 13.23 years). The average height and weight were 157.45 cm and 73.55 kg, respectively. The average of BMD measurements of lumbar spines L2-L4 was 1.04 gr/cm(2) (BMD = 85.65% and T score = -0.96) in the cases with SM. On the contrary, the average of the BMD measurements of lumbar spines L2-L4 was 1.05 gr/cm(2) (BMD = 101.14% and T score = 0.24) in the cases with SAM. The average of the BMD measurements of femoral neck was 0.85 gr/cm(2) (BMD = 91.39% and T score = -0.64) in the cases with SM. On the contrary, the average of the BMD measurements of femoral neck was 0.82 gr/cm(2) (BMD = 96.69% and T score = -0.31) in the cases with SAM. The bilateral oophorectomy as a surgical procedure is not a statistically significant factor for the acceleration of the bone loss. The main points are the age and the duration of menopause of the patient affecting the bone loss if the surgery is performed before menopause.

Genetics of osteoporosis

Genetic factors play an important role in regulating bone mineral density and other phenotypes relevant to the pathogenesis of osteoporosis such as ultrasound properties of bone, skeletal geometry, and bone turnover. Progress has been made in identifying quantitative traits for regulation of bone mineral density by linkage studies in man and mouse, but relatively few causal genes have been identified. Dramatic progress has been made in identifying the genes responsible for monogenic bone diseases and it appears that polymorphisms in many of these genes also play a role in regulating bone mineral density in the general population. Advances in knowledge about the genetic basis of osteoporosis and other bone diseases offer the prospect of developing new markers for assessment of fracture risk and the identification of novel molecular targets for the design of new drug treatments for osteoporosis.

An assessment of genetic markers as predictors of bone turnover in healthy adults

In 1992 a significant relationship between bone turnover and the vitamin D receptor (VDR) genotype was reported in Australian subjects of UK-Irish decent. Since then, several groups have investigated the relationship between VDR and other bone-related genotypes, bone mass and bone turnover in several populations. However, the results of these studies are conflicting. Therefore, our aim was to determine bone-related genotypes in a population of healthy Irish adults and relate these genotypes to the rate of bone turnover. One hundred and eighteen healthy Irish adults (aged 19-67 yr) were recruited and fasting blood and first void urines were collected from each subject. Bone-related genotype frequencies in healthy Irish adults were similar to those reported in other Caucasian populations and were in Hardy-Weinberg equilibrium. Estrogen receptor (Pvu II or Xba I), apolipoprotein E and collagen IA1 genotypes were not related to bone turnover. The tt VDR genotype was associated with significantly higher serum osteocalcin (29% and 40%) compared with the Tt and TT genotypes, respectively. The ff VDR genotype was associated with significantly higher urinary pyridinoline (by approximately 44% and approximately 29%) and deoxypyridinoline (by approximately 76% and approximately 58%) levels and higher serum osteocalcin (by approximately 25% and approximately 53%) compared with the Ff or FF genotypes, respectively. These findings suggest that healthy Irish adults with either the tt or ff VDR genotype have higher rates of bone turnover than those with Tt or TT, or Ff or FF genotypes, respectively, and therefore may have a higher risk of low bone mineral density and osteoporosis in later life.