Bone Mineral Content Measurements Research Articles

Histone de-acetylases and epigenetic regulation

Histone de-acetylases and epigenetic regulation

Normative data and percentile curves for Dual Energy X-ray Absorptiometry in healthy Indian girls and boys aged 5–17 years

For the correct interpretation of Dual Energy X-ray Absorptiometry (DXA) measurements in children, the use of age, gender, height, weight and ethnicity specific reference data is crucially important. In the absence of such a database for Indian children, the present study aimed to provide gender and age specific data on bone parameters and reference percentile curves for the assessment of bone status in 5–17year old Indian boys and girls. A cross sectional study was conducted from May 2006 to July 2010 on 920 (480 boys) apparently healthy children from schools and colleges in Pune City, India. The GE-Lunar DPX Pro Pencil Beam DXA scanner was used to measure bone mineral content (BMC [g]), bone area (BA [cm2]) and bone mineral density (BMD [g/cm2]) at total body, lumbar spine and left femur. Reference percentile curves by age were derived separately for boys and girls for the total body BMC (TBBMC), total body BA (TBBA), lumbar spine bone mineral apparent density (BMAD [g/cm3]), and left femoral neck BMAD. We have also presented percentile curves for TBBA for height, TBBMC for TBBA, LBM for height and TBBMC for LBM for normalizing bone data for Indian children. Mean TBBMC, TBBA and TBBMD were expressed by age groups and Tanner stages for boys and girls separately. The average increase in TBBMC and TBBA with age was of the order of 8 to 12% at each age group. After 16years of age, TBBMC and TBBA were significantly higher in boys than in girls (p<0.01). Maximal increase in TBBMD occurred around the age of 13years in girls and three years later in boys. Reference data provided may be used for the clinical assessment of bone status of Indian children and adolescents.

Cross-SectionalversusLongitudinal Associations of Lean and Fat Mass with pQCT Bone Outcomes in Children

Cross-sectional associations for lean mass (LM) and fat mass (FM) with bone may not reflect longitudinal associations. Cross-sectional and longitudinal associations of LM and FM with radial bone measurements in children were compared. We conducted a longitudinal study on 370 (232 females) children, 8-18 yr of age. LM and FM were measured by dual-energy absorptiometry. Peripheral quantitative computed tomography at the 4% radius (4R) and 20% radius (20R) measured bone mineral content (BMC), volumetric bone mineral density (vBMD), area, and strength [polar stress strain index (pSSI)]. Males at 20R had negative FM cross-sectional and longitudinal associations with cortical area and BMC and pSSI (P < 0.02); negative cross-sectional association with total area (P < 0.001); and negative longitudinal association with cortical thickness (P < 0.001). Females at 20R had FM cross-sectional association with total area, cortical BMC, and pSSI and longitudinal associations with cortical BMC and area, vBMD, and pSSI that went from positive to negative with age and, in some cases, varied with menarche. Both sexes at 4R had a negative FM cross-sectional association with BMC and area (P < 0.001) but negative longitudinal association with vBMD (P < 0.05). LM associations with bone outcomes were generally positive, except for negative longitudinal associations with cortical BMC and vBMD in young females (P < 0.01). LM associations were greater magnitude than FM associations and often depended on age. For males and older females, cross-sectional associations indicated a reduced bone size with higher FM, whereas longitudinal associations showed a decrease in cortical area without changes in bone size. LM was positively associated with BMC and area.

Bone Mineral Content Measured by DEXA Scan in Preterm Neonates Receiving Total Parentral Nutrition with and without Phosphorus Supplementation

Intravenous phosphorus preparation was not available in Egypt till recently. So we aimed to prove the positive effect of adding intravenous phosphorus to total parentral nutrition (TPN) on calcium (Ca) and phosphorus (PO4) metabolism ofpreterm neonates by measuring bone mineral content (BMC) using DEXA scan. A case-control study was conducted in NICU of Obstetric and Gynecology Hospital of Ain Shams University which is a tertiary care unit in Cairo. Thirty preterm infants were prospectively enrolled in the study divided into 2 groups; 15 preterm infants received TPN with phosphorus supplementation (group 1) and 15 preterm received TPN without phosphorus supplementation (group 2). Serum Ca, PO4 and alkaline phosphatase (ALP) assay were done together with urinary calcium/creatinine (Ca/Cr) ratio, abdominal ultrasound and DEXA scan. There were no significant difference regarding serum Ca and PO4 between group 1 and 2. Yet there were highly significant increase in serum ALP and urinary Ca/Cr ratio in group 2 compared to group 1 (p = 0.001). Also group 1 had significantly higher BMC compared to group 2 even with TPN duration less than 15 days (p = 0.001). BMC was significantly positively correlated with G.A and B.W in both groups and was significantly negatively correlated with serum ALP in group 2 and with urinary calcium/creatinine ratio in group 1. Duration of TPN as short as 2 weeks can affect negatively the BMC as documented by DEXA scan in preterm infants receiving TPN without phosphorus supplementation.

Improved accuracy of cortical bone mineralization measured by polychromatic microcomputed tomography using a novel high mineral density composite calibration phantom

Microcomputed tomography (micro-CT) is increasingly used as a nondestructive alternative to ashing for measuring bone mineral content. Phantoms are utilized to calibrate the measured x-ray attenuation to discrete levels of mineral density, typically including levels up to 1000 mg HA/cm3, which encompasses levels of bone mineral density (BMD) observed in trabecular bone. However, levels of BMD observed in cortical bone and levels of tissue mineral density (TMD) in both cortical and trabecular bone typically exceed 1000 mg HA/cm3, requiring extrapolation of the calibration regression, which may result in error. Therefore, the objectives of this study were to investigate (1) the relationship between x-ray attenuation and an expanded range of hydroxyapatite (HA) density in a less attenuating polymer matrix and (2) the effects of the calibration on the accuracy of subsequent measurements of mineralization in human cortical bone specimens. A novel HA-polymer composite phantom was prepared comprising a less attenuating polymer phase (polyethylene) and an expanded range of HA density (0-1860 mg HA/cm3) inclusive of characteristic levels of BMD in cortical bone or TMD in cortical and trabecular bone. The BMD and TMD of cortical bone specimens measured using the new HA-polymer calibration phantom were compared to measurements using a conventional HA-polymer phantom comprising 0-800 mg HA/cm3 and the corresponding ash density measurements on the same specimens. The HA-polymer composite phantom exhibited a nonlinear relationship between x-ray attenuation and HA density, rather than the linear relationship typically employed a priori, and obviated the need for extrapolation, when calibrating the measured x-ray attenuation to high levels of mineral density. The BMD and TMD of cortical bone specimens measured using the conventional phantom was significantly lower than the measured ash density by 19% (p < 0.001, ANCOVA) and 33% (p < 0.05, Tukey's HSD), on average, respectively. The BMD and TMD of cortical bone specimens measured using the HA-polymer phantom with an expanded range of HA density was significantly lower than the measured ash density by 8% (p < 0.001, ANCOVA) and 10% (p < 0.05, Tukey's HSD), on average, respectively. The new HA-polymer calibration phantom with a less attenuating polymer and an expanded range of HA density resulted in a more accurate measurement of micro-CT equivalent BMD and TMD in human cortical bone specimens compared to a conventional phantom, as verified by ash density measurements on the same specimens.

Age at Onset of Puberty Predicts Bone Mass in Young Adulthood

To determine whether the commencement and length of puberty influences dual x-ray absorptiometry (DXA) values of bone mineral content (BMC) and bone mineral density (BMD) in the axial and appendicular skeleton at skeletal maturity. From the Bone Mineral Density in Childhood Study, we identified children who began puberty and completed sexual and skeletal development and examined whether the timing and length of puberty influence DXA values of BMC and BMD at skeletal maturity. A total of 78 girls and 85 boys began puberty and completed skeletal maturity; 4.4 ± 0.8 and 4.5 ± 0.8 years later, respectively. Multiple linear regression analyses indicated that the age of onset of puberty was a strong negative predictor of DXA bone measurements at skeletal maturity, independent of bone values at the beginning of puberty, and the length of puberty. This negative relation was observed for all BMC and BMD measurements at all skeletal sites, in both boys and girls (all P < .0001). In contrast, length of puberty had no relation to any measures of bone. In healthy adolescent males and females, bone mass and bone density at skeletal maturity are inversely related to the timing of puberty.

A New Method in Measuring Bone Mineral Content by X-ray Densitometer

A New Method in Measuring Bone Mineral Content by X-ray Densitometer

Rapid in vivo whole body composition of rats using cone beam μCT

Precise, noninvasive analysis and quantification of in vivo body composition is essential for research involving longitudinal, small-animal disease models. We investigated the feasibility and precision of a rapid, flat-panel μCT scanner to report whole body adipose tissue volume (ATV), lean tissue volume (LTV), skeletal tissue volume (STV), and bone mineral content (BMC) in 25 postmortem female and 52 live male Sprague-Dawley rats. μCT images, acquired in three 90-mm segments and reconstructed with 308 μm of isotropic voxel spacing, formed contiguous image volumes of each entire rat specimen. Three signal-intensity thresholds (determined to be -186, 5, and 155 HU) were used to classify each voxel as adipose, lean, or skeletal tissue, respectively. Tissue masses from the volume fractions of ATV, LTV, and STV were calculated from assumed tissue densities of 0.95, 1.05, and 1.92 g/cm(-3), respectively. A CT-derived total mass was calculated for each rat and compared with the gravimetrically measured mass, which differed on average for the postmortem female and the live male group by 2.5 and 1.1%, respectively. To evaluate the accuracy of the CT-derived body composition technique, following the live male study excised muscle tissue in the lower right leg of all rats in group B were compared with the image-derived LT measurement of the same regional compartment and found to differ on average by 2.2%. Through repeated CT measurements of postmortem specimens, the whole body ATV, LTV, STV, and BMC measurement analysis gave a precision value of ±0.6, 1.9, 1.7, and 0.5% of the average value, respectively.

Impact of freezing on immunology and incorporation of bone allograft

With an increasing clinical use of deep frozen allograft for bone reconstruction, it is important to understand the immunological and biological events of allograft incorporation. In this study, we have investigated the impact of deep freezing on immunology and biopotency for incorporation of bone allografts. Deep frozen bone grafts matched or mismatched for major histoscompatibilty complex (MHC) were implanted in an 8-mm segmental defect in the tibia in rats. The construct was stabilized with intramedullary nailing. The immune response was evaluated by determination of serum antibody against the grafts MHC molecules at day 1 and after 2 and 4 months. Incorporation of the graft was compared with fresh syngeneic grafts and assessed with the use of conventional radiography, biomechanical testing and measurement of bone mineral content and density after 4 months. The analyses revealed no antibody responses in the rats that received grafts from donors differing at histocompatibility loci, and at 4 months the frozen grafts showed an overall reconstruction that was not significantly different from the fresh grafts. This study indicates that in the long run there are no significant consequences; either immunological or biomechanical, of the use of deep frozen allogenous bone as compared to fresh autogenous bone grafts in this animal model.

Bone mineral content and prostate cancer risk: data from the Baltimore Longitudinal Study of Aging

Aetiology (inception cohort) Level of Evidence 2b. To determine whether there might be differences in bone mineral content (BMC) between men who develop life-threatening prostate cancer and those who do not, as bone is a common site of prostate cancer metastases. From 1973 to 1984, BMC was serially measured in 519 participants (778 observations) as part of a longitudinal study of ageing. We examined the association between serial BMC measurements with the development of overall and high-risk prostate cancer over the next one to three decades. For all prostate cancer cases, BMC was censored at the time of diagnosis. During a median (range) overall follow-up of 21.1 (0.2-35.0) years after the last BMC measurement, 76 (14.6%) men were later diagnosed with prostate cancer (18 high-risk and 58 not high-risk). BMC declined with age to a greater extent in healthy controls than among men diagnosed with prostate cancer (P = 0.018, likelihood ratio test), and tended to decline less in high-risk than non-high-risk cases. The distribution of BMC was significantly different between men who did and did not develop prostate cancer, over an extended follow-up. Specifically, BMC appeared to decline to a greater extent with age among healthy controls than in men with prostate cancer, especially high-risk disease. The biology underlying the lesser decline in BMC among men with prostate cancer remains unclear, but suggests that host factors in the bony milieu might be associated with prostate cancer development and progression.

Calcium supplementation for 2 years improves bone mineral accretion and lean body mass in Chinese adolescents.

to study the effects of different doses of calcium intake on bone health and body composition in Chinese adolescents. a double-blind randomized controlled trial of calcium carbonate supplementation in 257 healthy adolescents aged 12-15 years old for 24 months. Subjects were randomly assigned to four groups receiving chewable calcium carbonate tablets providing elemental calcium at 63 mg/d, 354 mg/d, 660 mg/d, 966 mg/d, respectively. At the end of intervention, we reclassified 197 adolescents into 3 groups who had received actual doses of elemental calcium of 85 mg/d (Low dose), 230 mg/d (Medium dose) and 500 mg/d (High dose). We measured bone mineral content (BMC), bone mineral density (BMD) and body composition by dual-energy X-ray absorptiometry. BMC and BMD of total body and lumbar spine were increased significantly in both males and females after intervention at all doses (p<0.05). In males, after supplementation, total body BMC in the medium and high dose groups (2464 g and 2437 g, respectively) was significantly higher than that in the low dose group (2321 g) after adjusting for age, pubertal development, BMI, physical activity and energy intake; in addition, lean body mass in the medium and high dose groups (49.1 kg and 48.8 kg, respectively) was significantly higher than that in the low dose group (46.7 kg) (p<0.05). There was no significant effect of calcium supplementation on bone mass or body composition in females. calcium supplementation more than 230 mg/d for two years can improve bone mineral accretion and lean body mass in Chinese male adolescents.

The muscle–bone unit of peripheral and central skeletal sites in children and young adults

Changes and gender differences in the muscle bone unit at different skeletal sites were investigated during pubertal development. Females accrued greater BMC in relation to muscle compared to males; these gender differences were greater after adjustment for height and regional fat mass. To describe changes and gender differences in the muscle-bone unit at different skeletal sites during pubertal development. Four hundred forty-two children aged 5-18years were studied. Measurements of bone mineral content (BMC), lean mass (LM) and fat mass of the whole body (WB), legs, arms and lumbar spine were obtained from dual-energy X-ray absorptiometry. Peripheral quantitative computed tomography was used to measure BMC of the radius diaphysis and cross-sectional muscle area (CSMA) of the mid-forearm. These measurements were used to describe differences between, and within, genders at each pubertal stage in BMC accrual relative to muscle, both before and after adjustment for height, regional fat and muscle at central and peripheral skeletal sites. In males, there were significant increases in adjusted WB and leg BMC at the end of pubertal development. Unadjusted and adjusted lumbar spine BMC increased at the onset of, and at the end, of puberty. Radius BMC increased at most pubertal stages. In females, there were increases in unadjusted and adjusted whole body BMC at late puberty, in leg BMC at the onset of puberty and at pubertal stage four. Unadjusted arm BMC increased at most pubertal stages; however, after adjustment, an increase occurred at pubertal stage four. Both adjusted and unadjusted lumbar spine BMC increased at pubertal stage four. Unadjusted radius BMC increased at most pubertal stages. Females had greater BMC at all skeletal sites, compared to males, except at the radius, where adjusted BMC was greater in males at pubertal stage four. Males and females accrue more BMC in relation to lean mass at multiple skeletal sites as puberty proceeds. Females accrue more BMC in relation to lean mass, in comparison to males, at most skeletal sites.

Consumption of krill protein concentrate prevents early renal injury and nephrocalcinosis in female Sprague–Dawley rats

Female Sprague-Dawley rats provide an animal model for studying the role of nutrition in renal health due to their sensitivity to diet-induced alterations in kidney function. Nephrocalcinosis, a common renal abnormality found in rats, has been implicated in subsequent renal failure. Simple dietary manipulations, such as changing the source of dietary protein, may influence nephrocalcinosis. This study evaluates the consumption of krill protein concentrate (KPC), a novel and high-quality protein, on renal and bone health. Young female Sprague-Dawley rats (n = 10/group) were individually housed in metabolic cages and fed ad libitum diets consisting of 10% crude protein supplied as KPC or casein for 4 weeks. Diets were isocaloric, isonitrogenous, and matched for calcium (Ca) and phosphorus (P). Urinary n-acetyl glucosaminidase (NAG) was measured and kidney histology performed to assess kidney damage. Biomarkers of kidney function were determined by calorimetric assays. Ca and P balance and bone concentrations were measured using inductively coupled plasma mass spectrometry. Femoral strength was determined by three-point bend testing. Rats fed KPC had lower (P = 0.005) urinary NAG levels and minimal microtubular Ca deposition compared to rats fed casein. There was a tendency (P < 0.06) for higher glomerular filtration rates and lower proteinuria, and higher (P = 0.03) urinary output in rats fed KPC compared to casein. There were no differences in Ca and P balance or bone measurements of total bone mineral content, Ca, P or strength between rats fed KPC and casein. Based on the study results, KPC prevented early renal injury leading to nephrocalcinosis and potential bone loss.

Antiretroviral therapy and bone mineral measurements in HIV-infected youths

Reduced bone mass measurements are often found in HIV-infected youths. Both in vitro and human studies demonstrated a role of antiretroviral treatment in determining bone mass alteration. Nevertheless, the data regarding the responsibility of different antiretroviral drugs on bone health in children and adolescents are highly controversial. The purpose of the current study was to relate antiretroviral treatment to bone mass measurements in a large cohort of HIV-infected children and adolescents. Bone mineral content (BMC) was measured in 86 HIV-infected youths (aged 4.8–22.1 years), and in 194 healthy controls (aged 4.9–21.9 years). Fifteen patients were naive to antiretroviral treatment, 11 were receiving a dual nucleoside reverse transcriptase inhibitor (NRTIs) combination, 32 a protease inhibitor (PI)-based antiretroviral treatment, and 28 a non-nucleoside reverse transcriptase inhibitor (NNRTIs)-based regimen. Comparisons between healthy and HIV-infected children and adolescents have been performed by multiple regression analyses to correct for differences in age, sex, and anthropometric measurements. Patients receiving a PI-based treatment had lumbar spine and whole body BMC values significantly lower than healthy children ( P < 0.05). BMC measurements of patients on other therapeutic regimens or naive to antiretroviral treatment did not differ significantly from those of healthy children. Among patients receiving a PI-based regimen, those receiving full dose Ritonavir had significantly lower lumbar spine BMC values compared to other patients. Lumbar spine and whole body BMC measurements of patients receiving a Stavudine-containing regimen were lower compared to healthy controls, naive patients, and patients on other antiretroviral regimens. Multivariate analyses showed that patients receiving both Stavudine and full dose Ritonavir had significantly lower BMC values both at the lumbar spine ( P = 0.0033), and in the whole skeleton ( P = 0.05). In conclusion, antiretroviral treatment may have a detrimental effect on bone health of HIV-infected youths: the use of Ritonavir full dose alone or in combination with Stavudine is associated to lower bone mass measurements. The use of antiretroviral regimens including these drugs should thus be monitored closely in HIV-infected youths.

Comparison of Bone Mineral Parameter Measurements by Dual-Energy X-ray Absorptiometry With Bone Stiffness Measurements as Indicators of the Load-Bearing Capacity of Regenerating Bone

The objective of this study was to compare bone mineral density and content measurements by dual-energy x-ray absorptiometry with bone stiffness measurements as indicators of the load-bearing capacity of regenerating bone during distraction osteogenesis. The study analyzed ex vivo a set of 26 sheep bone specimens after distraction osteogenesis. Bone mineral density and bone mineral content were measured by dual-energy x-ray absorptiometry. Biomechanical parameters such as torsional, compressive, and bending stiffness were determined using a material testing system. The maximum torsional moment applied at fracture is used to determine the load-bearing capacity of the bone. The correlation between stiffness measurements and the load-bearing capacity of a bone is significantly greater than the correlation between load-bearing capacity and bone mineral density and content measurements by dual-energy x-ray absorptiometry. The results of this ex vivo study indicate that stiffness measurements are a better quantitative indicator of the load-bearing capacity of a bone and thus of bone healing than bone mineral density and content measurements by dual-energy x-ray absorptiometry. The results of the current study do not confirm previous work that showed that there is a significant correlation between bone material quality obtained by dual-energy x-ray absorptiometry and bone strength.

Height adjustment in assessing dual energy x-ray absorptiometry measurements of bone mass and density in children.

In children, bone mineral content (BMC) and bone mineral density (BMD) measurements by dual-energy x-ray absorptiometry (DXA) are affected by height status. No consensus exists on how to adjust BMC or BMD (BMC/BMD) measurements for short or tall stature. The aim of this study was to compare various methods to adjust BMC/BMD for height in healthy children. Data from the Bone Mineral Density in Childhood Study (BMDCS) were used to develop adjustment methods that were validated using an independent cross-sectional sample of healthy children from the Reference Data Project (RDP). We conducted the study in five clinical centers in the United States. We included 1546 BMDCS and 650 RDP participants (7 to 17 yr of age, 50% female). No interventions were used. We measured spine and whole body (WB) BMC and BMD Z-scores for age (BMC/BMD(age)), height age (BMC/BMD(height age)), height (BMC(height)), bone mineral apparent density (BMAD(age)), and height-for-age Z-score (HAZ) (BMC/BMD(haz)). Spine and WB BMC/BMD(age)Z and BMAD(age)Z were positively (P < 0.005; r = 0.11 to 0.64) associated with HAZ. Spine BMD(haz) and BMC(haz)Z were not associated with HAZ; WB BMC(haz)Z was modestly associated with HAZ (r = 0.14; P = 0.0003). All other adjustment methods were negatively associated with HAZ (P < 0.005; r = -0.20 to -0.34). The deviation between adjusted and BMC/BMD(age) Z-scores was associated with age for most measures (P < 0.005) except for BMC/BMD(haz). Most methods to adjust BMC/BMD Z-scores for height were biased by age and/or HAZ. Adjustments using HAZ were least biased relative to HAZ and age and can be used to evaluate the effect of short or tall stature on BMC/BMD Z-scores.

Bone mineral content in young adults with active or inactive juvenile idiopathic arthritis and in controls

Objective: To obtain information on bone mineral content (BMC) in juvenile idiopathic arthritis (JIA) in young adulthood.Methods: BMC measurements of 116 young adults with JIA and controls were performed at the lumbar spine and the proximal femur by dual-energy X-ray absorptiometry (DXA).Results: Patients were divided into the JIA-active group (n = 73) and the JIA-inactive group (n = 43). Fifty-five per cent of men and 30% of women had their disease in remission. Forty-eight per cent in the JIA-active group and 16% in the JIA-inactive group had used glucocorticoids (p < 0.001). Mean BMC in the femoral neck was 5.76 (SD 0.21) g for men and 4.74 (SD 0.10) g for women in the JIA-active group; 5.84 (SD 0.23) g for men and 4.59 (SD 0.06) g for women in the JIA-inactive group; and 6.65 (SD 0.20) g for men and 4.78 (SD 0.07) g for women in the controls. Both JIA groups had lower BMC values in the femoral neck than the controls (p < 0.001), but a statistically significant difference was found among men (p = 0.006). There was no significant difference in mean BMC in the lumbar spine between the JIA groups and the controls, nor between men and women. Glucocorticoid use, weight and also height among women were associated statistically significantly with BMC in the femoral neck.Conclusions: Young adults, especially men, with JIA have reduced BMC values in the femoral neck. Glucocorticoid use and weight, but not disease activity, seem to be associated with lower BMC. However, osteoporosis is rare.

Impact of freezing on bone graft incorporation biomechanical evaluations in rats

Background With an increasing clinical application of grafting for bone reconstruction, it is important to understand the physiological and biological events of graft incorporation. In this study, we have investigated the impact of deep freezing on the biopotency for incorporation of bone grafts. Methods Fresh and deep-frozen autogenous bone grafts were implanted in an 8-mm segmental defect in the tibia. The construct was stabilized with intramedullary nailing. Incorporation of the graft was assessed with use of conventional radiography, biomechanical testing and measurements of bone mineral content and density after 2 and 4 months, respectively. Findings Frozen grafts were significantly less integrated after 2 months as compared to fresh grafts. After 4 months, however, the frozen grafts showed an overall reconstruction that was not significantly different from the fresh grafts. Both frozen and fresh grafted segments had only reached 70% strength of intact bone at 4 months. Interpretation This study indicates that in the long run there are no significant consequences, radiologically or biomechanically, of deep freezing as compared to fresh bone grafts.

A calcitonin receptor (CALCR) single nucleotide polymorphism is associated with growth performance and bone integrity in response to dietary phosphorus deficiency

Although concerns over the environmental impact of excess P in the excreta from pig production and governmental regulations have driven research toward reducing dietary supplementation of P to swine diets for over a decade, recent dramatic increases in feed costs have further motivated researchers to identify means to further reduce dietary P supplementation. We have demonstrated that genetic background impacts P utilization in young pigs and have identified genetic polymorphisms in several target genes related to mineral utilization. In this study, we examined the impact of a SNP in the calcitonin receptor gene (CALCR) on P utilization in growing pigs. In Exp. 1, 36 gilts representing the 3 genotypes identified by this CALCR SNP (11, 12, and 22) were fed a P-adequate (PA) or a marginally P-deficient (approximately 20% less available P; PD) diet for 14 wk. As expected, P deficiency reduced plasma P concentration, bone strength, and mineral content (P < 0.05). However, the dietary P deficiency was mild enough to not affect the growth performance of these pigs. A genotype x dietary P interaction (P < 0.05) was observed in measures of bone integrity and mineral content, with the greatest reduction in bone strength and mineral content due to dietary P deficiency being associated with the allele 1. In Exp. 2, 168 pigs from a control line and low residual feed intake (RFI) line were genotyped for the CALCR SNP and fed a PA diet. As expected, pigs from the low RFI line consumed less feed but also gained less BW when compared with the control line (P < 0.05). Although ADFI did not differ between genotypes, pigs having the 11 genotype gained less BW (P < 0.05) than pigs having the 12 or 22 genotypes. Pigs of the 11 and 12 genotypes had bones that tolerated greater load when compared with animals having the 22 genotype (P < 0.05). A similar trend was observed in bone modulus and ash % (P < 0.10). These data are supportive of the association of this CALCR SNP with bone integrity and its response to dietary P restriction. Although the allele 1 is associated with greater bone integrity and mineral content during adequate P nutrition, it is also associated with the greatest loss in bone integrity and mineral content in response to dietary P restriction. Understanding the underlying genetic mechanisms that regulate P utilization may lead to novel strategies to produce more environmentally friendly pigs.

Normalization Of Factors Influencing Bone Mineral Content Measures In Young Children.

When examining the effect of intervention strategies on the bone mineral content (BMC; g) measures of young children, several anthropometric and body composition covariates should be taken into consideration and their influence should be statistically removed. These covariates may include height (cm), fat mass (FM; g) and mineral-free lean mass (MFL; g). PURPOSE: To determine the appropriateness of normalizing data as a method to reduce the covariate effects of height, FM and MFL on total body and regional BMC measures in young children. METHODS: Subjects included 571 children ages 5 to 11 yrs old with a varying distribution of BMI for age and sex classifications. A wall-fixed stadiometer was used to determine height and total body dual energy x-ray absorptiometry scans were used to measure FM, MFL, and BMC of the arms, legs, trunk, and total body. The best fit power exponent (b) between BMC and covariate (x) in the form of BMC = kxb (where k is a constant) was determined using the log-log transformation method. RESULTS: To eliminate the covariate effect of height from the BMC of the arms, legs, trunk and total body, the child's height should be normalized by the power exponent value b (± 95% confidence interval) of 3.87 ± 0.14, 4.55 ± 0.14, 3.76 ± 0.16, and 3.19 ± 0.12, respectively. To eliminate the covariate effect of FM from the BMC of the arms, legs, trunk and total body, the child's FM should be normalized by the power exponent value b of 0.36 ± 0.03, 0.44 ± 0.03, 0.39 ± 0.02, 0.32 ± 0.02, respectively. To eliminate the covariate effect of MFL from the BMC of the arms, legs, trunk and total body, the child's MFL should be normalized by the power exponent value b of 1.60 ± 0.04, 1.85 ± 0.05, 1.59 ± 0.05, 1.33 ± 0.03, respectively. CONCLUSIONS: Future research should confirm the theoretical rationale for the covariate factors and the best fit power exponents when BMC and other bone variables are examined in young children.