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Biomedical subjects

R Marcus

Publications and source records attributed to R Marcus.

At least 91 records · Page 5Linked to original sources
PubMed1997

Skeletal status of men with early and late ankylosing spondylitis.

PURPOSE: To assess the influence of extent of disease on the skeletal status of men with ankylosing spondylitis (AS). PATIENTS AND METHODS: Fourteen men with AS were studied at entry and again after 15 months. Bone mineral density (BMD) was assessed by single photon absorptiometry (SPA), dual energy x-ray absorptiometry (DXA), and quantitative computed tomography (QCT). Calciotropic hormones and bone turnover were also assessed, and biopsies of iliac crest and skin were taken after tetracycline double-labeling from 10 subjects. Clinical evaluation and Health Assessment Questionnaires were used to assess functional status. RESULTS: Of the 14 participants, 7 had sacroiliitis alone without radiologic evidence of spinal involvement (early disease) and 7 had sacroiliitis with extensive vertebral calcifications and immobilization (late disease). QCT baseline lumbar spine BMD was very low in both groups compared with normative standards (Z score = -3.08 +/- 1.83, P < 0.0001) and did not change significantly over 15 months. This low BMD was more marked in late disease than in early disease subjects (P < 0.01). DXA BMD at the lumbar spine was lower than predicted in early disease subjects (Z score = -1.08 +/- 0.67, P = 0.005) but not in the late disease group. DXA BMD was also low at the all three hip sites (Z score = -0.96 +/- 0.86, P < 0.01). Significant differences between late disease group and normative values were apparent at all hip sites. Values in early disease subjects, however, did not differ from age-predicted norms. Bone mineral status did not change significantly over the 15-month period of observation. Circulating parathyroid hormone (PTH) and vitamin D metabolites were normal in both groups as were creatinine clearance and urinary excretion of calcium and hydroxyproline. Osteocalcin levels were normal in all but the two youngest subjects in the early disease group. Histomorphometry of the iliac crest showed no consistent change in bone turnover. Bone volume and trabecular width were low in many cases. Cancellous bone volume correlated with lumbar spine BMD by QCT (r = 0.69, P = 0.026) but not with DXA. Although beneficial changes occurred in exercise tolerance and pain over time, anthropometric measurements did not improve. CONCLUSION: BMD is low in both the axial and peripheral skeleton in men with AS and is independent of spinal immobilization. Anterioposterior lumbar spine DXA in late AS is less useful than QCT in determining the degree of osteopenia in late AS. Bone mineral deficits in AS do not reflect measurable metabolic derangement or hypogonadism. Although bone histomorphometry suggests both trabecular thinning and loss of structural elements as mechanisms involved in low bone volume, the exact cause of osteopenia in AS remains to be determined.

Absorptiometry, Photon↗
PubMed1997

Dynamic muscle strength alterations to detraining and retraining in elderly men.

To investigate the effects of cessation and subsequent resumption of training on muscle strength in elderly men, 11 men (aged 65-77 years), just completing a 24-week randomized controlled trial of recombinant human growth hormone (rhGH) and resistance exercise (rhGH, n = 6; placebo, n = 5), detrained for 12 weeks and subsequently retrained for 8 weeks. During the detraining and retraining phase, subjects did not receive rhGH. The resistance programme included three sets of eight repetitions at 75% of one-repetition maximum (1-RM), three times per week, for 10 upper and lower body exercises. Dynamic muscle strength was assessed by the 1-RM method every 2 weeks for 44 weeks. Needle biopsies of vastus lateralis muscle were obtained from seven men. Muscle strength increased during initial training by 40.4 +/- 5.5% (mean +/- SEM), ranging from 26.0 +/- 5.0 to 83.9 +/- 15.6%, depending on muscle group. Increased strength was accompanied by hypertrophy (P < 0.05) of type I (17.4 +/- 4.1%) and II (25.8 +/- 12.4%) muscle fibres. Of initial strength gains, only 29.9 +/- 5.2% was lost with detraining. However, type I and II fibre cross-sectional area reverted to pretraining values. After 8 weeks of retraining, muscle strength returned to trained values, but without a significant change in fibre morphology. The results indicate that elderly men lose some muscle strength following short-term detraining, but that only a brief period of retraining suffices to regain maximal strength. Reversal of fibre cross-sectional area with detraining, and only modest improvement with retraining, suggests that much of the retention in strength with detraining and reacquisition of lost strength with retraining reflects neural adaptation.

Aged↗
PubMed1997

Effect of rhGH and rhIGF-I treatment on protein utilization in elderly women.

To assess the effect of recombinant human growth hormone (rhGH) and recombinant human insulin-like growth factor I (rhIGF-I) on protein utilization, 14 women, age 66-82 yr, were invited to participate in studies of nitrogen balance (n = 14), whole body protein turnover (n = 14), and muscle protein synthesis (n = 8). They were studied both 1 wk before and during the last week of a 1-mo regimen, to which they had been randomly assigned, of either 0.025 mg rhGH/kg once daily or rhIGF-I at 0.015 (low), 0.03 (mid), or 0.06 (high) mg/kg twice daily. Nitrogen balance increased significantly after 1 wk of treatment in all groups (P < 0.05). After 1 mo, the magnitude of this effect had diminished by 50% in the rhGH group but remained elevated throughout the treatment period with all doses of rhIGF-I. Both protein synthesis and breakdown, measured by a primed constant infusion of [15N]glycine, were significantly increased with rhGH (9% and 8%, respectively), low-dose rhIGF-I (4.5% and 4%), and high-dose rhIGF-I (18% and 17%). Net synthesis was significantly increased with rhGH (48%) and high- and mid-dose rhIGF-I (27% and 196%, respectively). Muscle protein synthesis as measured by incorporation of [1-13C]leucine increased significantly with rhGH (50%) and the mid (67%) and high (57%) doses of rhIGF-I. These data show that whole body and muscle protein synthesis are responsive to growth factor stimulation in elderly women.

Aged↗
PubMed1997

Skeletal effects of growth hormone and IGF-I in adults.

Three processes occur in the skeleton; modelling during growth, fracture repair and remodelling. Remodelling is bone resorption coupled to bone formation, and alterations in the remodelling balance are the final pathway to bone loss. Therapeutic agents are now available to minimize the normal phenomenon of age-related bone loss and protect against osteoporotic fracture. These agents reduce the rate of bone resorption, have positive effects on bone mass and some reduce fracture rates. None, however, restore bone mineral to normal levels. GH has been considered for this role due to its positive effects in vitro and in vivo. GH-deficient adults have low BMD compared to healthy controls, and the reasons for this finding are discussed. A neglected factor is a measurement artefact from the use of DXA. Long-term GH therapy can lead to clinically important increases in BMD in GH-deficient adults. The results from studies of GH administration to healthy elderly populations are also presented. The small rise of lumbar BMD or maintenance of BMD at the hip seen in these studies are no better than results achieved with cheaper, easier to administer therapies. Investigation of other agents in the somatotrophic axis, are, however, potentially promising and warrant further investigation.

Adult↗
PubMed1997

Skeletal effects of cyclic recombinant human growth hormone and salmon calcitonin in osteopenic postmenopausal women.

The objectives of this study were to determine whether cyclic administration of recombinant human GH, with or without the antiresorptive agent, salmon calcitonin (CT), provides clinically meaningful increases in bone mineral density (BMD) at the lumbar spine and proximal femur in postmenopausal osteopenic women. The design of the study was a randomized clinical trial consisting of 12 56-day treatment cycles. Each cycle was initiated by a 12-day period of hormone administration, followed by 44 days of supplemental calcium only. Cycles of hormone administration consisted of 7 daily injections of recombinant GH (20 micrograms/kg.day) or its placebo, followed by 5 daily injections of salmon CT (100 U/day) or its placebo. The study was performed at the Palo Alto Veterans Affairs medical center. The patients were 84 healthy women with lumbar spine BMD more than 1 SD below the average value for a healthy 25-yr-old Caucasian woman. BMD was measured at the lumbar spine and proximal femur by dual energy x-ray absorptiometry. Biochemical markers of bone turnover and circulating insulin-like growth factor I were also measured. GH treatment increased insulin-like growth factor I concentrations from low values at baseline (112 +/- 56 ng/mL) to the young normal range (approximately 430 +/- 125 ng/mL). Groups receiving GH plus CT or GH plus placebo increased lumbar spine BMD at 2 yr by 2.70 +/- 0.81% (P < 0.01) and 1.72 +/- 0.74% (P < 0.05; intention to treat analysis). No significant change occurred in women receiving placebo plus CT or combined placebo. Significant increases in total hip BMD of 1-2% were observed for the GH plus placebo and placebo plus CT groups, with a nonsignificant trend in the GH plus CT group. For the femoral trochanter, significant increases were observed in the GH plus CT and placebo plus CT groups only. No significant change in femoral neck BMD was observed in any group. Women taking replacement estrogen had the same BMD response as those who were estrogen deficient. No significant increase in BMD was observed between 24 and 36 months in the 62 women who returned for a 3 yr measurement. In response to GH, short term increases in resorption and formation markers were observed, but these had decreased before the next treatment cycle. No long term changes in resorption markers were observed, but women in the GH groups showed a sustained rise in circulating osteocalcin over the entire 2-yr protocol. GH given cyclically with or without CT for 2 yr achieved statistically significant increases in BMD of the lumbar spine and selected areas of the hip in postmenopausal women. These gains were less marked than those achieved with estrogen or bisphosphonates and were associated with a relatively high incidence of adverse experiences. Therefore, it is unlikely that cyclic GH with or without CT will prove clinically useful in the treatment of postmenopausal women with osteoporosis.

Aged↗
PubMed1997

Bone mass and hip axis length in healthy Asian, black, Hispanic, and white American youths.

The primary objective of this study was to examine the associations of ethnicity, diet (calcium, protein, energy), and weight-bearing activity with dual-energy X-ray absorptiometry (DXA)-measured bone mass and hip axis length (HAL) in 423 Asians, blacks, Hispanics, and non-Hispanic Caucasians, aged 9-25 years. Bone mass was expressed as bone mineral content (BMC), bone mineral density (BMD), and bone mineral apparent density (BMAD). The data were analyzed using multiple linear regression, after stratifying for gender and pubertal stage and adjusting for height and weight. With few exceptions, Asians and Hispanics had comparable bone mass to whites at all pubertal stages. Greater femoral neck BMAD in black than white females was observed at all pubertal stages. Black males displayed greater BMD and BMAD than white males at all sites in early puberty and at the femoral neck in maturity. Calcium was positively and protein negatively related to BMAD at the femoral neck in early pubertal females. Among males, calcium was negatively associated with whole body BMC and BMD and spine BMD and BMAD in midpuberty. Weight-bearing activity was not associated with bone mass in females; in males, it was positively related only to femoral neck BMC in early puberty. There was an absence of evidence for ethnic differences in HAL among females. In males, we observed shorter HAL in mature Asians and blacks than whites. Neither diet nor activity was associated with HAL.

Absorptiometry, Photon↗
PubMed1997

Vitamin D receptor polymorphisms, bone mineral density, and bone metabolism in postmenopausal Mexican-American women.

Common polymorphisms in the vitamin D receptor (VDR) gene have been shown to correlate with bone mineral density (BMD). However, attempts to replicate the original findings in other populations have yielded variable results. These disparities may reflect ethnic or environmental differences in the expression of the VDR effect upon BMD. We examined a relatively ethnically homogeneous group of 103 healthy postmenopausal Caucasian women of Mexican descent living in Northern California. We determined the VDR genotype and measured the BMD at the lumbar spine and femoral neck by dual-energy X-ray absorptiometry, as well as several biochemical indices of mineral metabolism. The prevalence of the BB genotype, associated in previous studies with the lowest BMD, was 8% and highly linked to the tt genotype. Absolute and age-adjusted BMD at both hip and spine showed a trend toward lower BMD in the BB, AA, and tt genotypes, but this trend did not achieve statistical significance. There were no consistent intergroup differences in change in BMD over 2 years of follow-up, nor in mean serum concentrations of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, osteocalcin, or total urinary pyridinolines. Intact parathyroid hormone concentrations were significantly higher in subjects with the AA genotype, with a trend toward higher values in those with the BB and tt genotypes as well. Our data suggest that there may be a decrease in BMD associated with the B, A, and t alleles, but the intergroup difference in BMD is 0.2-0.5 standard deviations (SD) at the lumbar spine and 0.3 SD at the femoral neck, decreases that are smaller than previously reported. Given the relatively low prevalence of the BB/tt genotype in Mexican-American Caucasians, a larger sample would be required to detect a significant association between VDR alleles and differences in BMD of the magnitude suggested by our data. We conclude that a genotype effect of this magnitude, if present, would be clinically relevant, but the impact on BMD is too small to detect with statistical significance in a study of this size.

Aged↗
PubMed1997

High-impact exercise promotes bone gain in well-trained female athletes.

Maximizing peak bone mass, as well as reducing its loss after menopause, is important for the prevention of osteoporosis. One mode of activity, gymnastics training, invokes high impact loading strains on the skeleton which may have powerful osteogenic effects. To examine the role of athletic activity, specifically gymnastics, on bone mineral density (BMD) accretion, we monitored longitudinal changes in regional and whole body BMD in collegiate women gymnasts and competitive athletes whose skeletons are exposed to differential loading patterns: runners and swimmers. Two cohorts were studied. Cohort I = 26 gymnasts (19.7 +/- 1.2 years), 36 runners (21.1 +/- 2.7 years) and 14 nonathletic women (19.3 +/- 1.7 years) followed over an 8-month period. Cohort II = 8 gymnasts (18.9 +/- 1.1 years), 11 swimmers (20.0 +/- 2.3 years) and 11 nonathletic women (19.0 +/- 1.2 years) followed over a 12-month period. Lumbar spine (L2-4), femoral neck, and whole body BMD (g/cm2) were assessed by dual-energy X-ray absorptiometry. For cohort I, the percent change in lumbar spine BMD after 8 months was significantly greater (p = 0.0001) in the gymnasts (2.8 +/- 2.4%) than in the runners (-0.2 +/- 2.0%) or controls (0.7 +/- 1.3%). An increase in femoral neck BMD of 1.6 +/- 3.6% in gymnasts was also greater (p < 0.05) than runners (-1.2 +/- 3.0%) and approached significance compared with controls (-0.9 +/- 2.2%, p = 0.06). For cohort II, gymnasts gained 2.3 +/- 1.6% at the lumbar spine which differed significantly (p < 0.01) from changes in swimmers (-0.3 +/- 1.5%) and controls (-0.4 +/- 1.7%). Similarly, the change at the femoral neck was greater (p < 0.001) in gymnasts (5.0 +/- 3.4%) than swimmers (-0.6 +/- 2.8%) or controls (2.0 +/- 2.3%). The percent change in BMD at any site did not differ between eumenorrheic and irregularly menstruating athletes. These results indicate that bone mineral at clinically relevant sites, the lumbar spine and femoral neck, can respond dramatically to mechanical loading characteristic of gymnastics training in college-aged women. This occurred despite high initial BMD values and was independent of reproductive hormone status. The results provide evidence to support the view that high impact loading, rather than selection bias, underlies high BMD values characteristic of women gymnasts. Because all athletes underwent resistance training throughout the year of study, muscle strengthening activity did not appear to be a significant factor in the skeletal response observed in gymnasts. We conclude that activities resulting in high skeletal impacts may be particularly osteotropic for young women.

Absorptiometry, Photon↗
PubMed1996

Allogeneic bone marrow transplantation versus autologous stem cell transplantation in multiple myeloma: a retrospective case-matched study from the European Group for Blood and Marrow Transplantation.

A retrospective case-matched analysis was performed comparing 189 myeloma patients treated with allogeneic bone marrow transplantation (allo-BMT) with an equal number of patients who received autologous stem cell transplantation (ASCT). Matching was performed with respect to gender and number of treatment lines before transplantation. The groups were comparable with the exception of median age (43 years for allo-BMT v 49 years for ASCT, P = .0001) and median posttransplant follow-up (46 months for allo-BMT v 30 months for ASCT, P = .0003). The overall survival was significantly better for ASCT than for allo-BMT, with a median survival of 34 months and 18 months, respectively (P = .001). However, this survival advantage was only observed in men, but not in women. The statistically significant survival advantage for ASCT was seen in most subgroups, ie, chemotherapy-responsive patients, patients who had received two or more treatment lines before transplantation, patients in partial remission, patients with an IgG-subtype, patients older than 46 years of age, patients with stage II disease, and patients with a low or high serum-beta-2-microglobulin at diagnosis. The main reason for the poorer survival in allo-BMT patients was higher transplant-related mortality (41% v 13% for ASCT, P = .0001), which was not compensated for by a lower rate of relapse and progression. However, in patients alive at 1 year posttransplant, there was a trend for better long-term survival (P = .09) and significantly better progression-free survival (P = .02) for allo-BMT as compared with ASCT. We conclude that the median survival is superior for ASCT. However, allo-BMT has a lower relapse rate, which results in a similar long-term outcome for both approaches, but a longer follow-up is needed to assess the final outcome.

Acute Disease↗
PubMed1996

Randomised trial of effect of alendronate on risk of fracture in women with existing vertebral fractures. Fracture Intervention Trial Research Group.

BACKGROUND: Previous studies have shown that alendronate can increase bone mineral density (BMD) and prevent radiographically defined (morphometric) vertebral fractures. The Fracture Intervention Trial aimed to investigate the effect of alendronate on the risk of morphometric as well as clinically evident fractures in postmenopausal women with low bone mass. METHODS: Women aged 55-81 with low femoral-neck BMD were enrolled in two study groups based on presence or absence of an existing vertebral fracture. Results for women with at least one vertebral fracture at baseline are reported here. 2027 women were randomly assigned placebo (1005) or alendronate (1022) and followed up for 36 months. The dose of alendronate (initially 5 mg daily) was increased (to 10 mg daily) at 24 months, with maintenance of the double blind. Lateral spine radiography was done at baseline and at 24 and 36 months. New vertebral fractures, the primary endpoint, were defined by morphometry as a decrease of 20% (and at least 4 mm) in at least one vertebral height between the baseline and latest follow-up radiograph. Non-spine clinical fractures were confirmed by radiographic reports. New symptomatic vertebral fractures were based on self-report and confirmed by radiography. FINDINGS: Follow-up radiographs were obtained for 1946 women (98% of surviving participants). 78 (8.0%) of women in the alendronate group had one or more new morphometric vertebral fractures compared with 145 (15.0%) in the placebo group (relative risk 0.53 [95% Cl 0.41-0.68]). For clinically apparent vertebral fractures, the corresponding numbers were 23 (2.3%) alendronate and 50 (5.0%) placebo (relative hazard 0.45 [0.27-0.72]). The risk of any clinical fracture, the main secondary endpoint, was lower in the alendronate than in the placebo group (139 [13.6%] vs 183 [18.2%]; relative hazard 0.72 [0.58-0.90]). The relative hazards for hip fracture and wrist fracture for alendronate versus placebo were 0.49 (0.23-0.99) and 0.52 (0.31-0.87). There was no significant difference between the groups in numbers of adverse experiences, including upper-gastrointestinal disorders. INTERPRETATION: We conclude that among women with low bone mass and existing vertebral fractures, alendronate is well tolerated and substantially reduces the frequency of morphometric and clinical vertebral fractures, as well as other clinical fractures.

Aged↗
PubMed1996

Differences in bone mineral in young Asian and Caucasian Americans may reflect differences in bone size.

Bone mineral content (BMC) and areal bone mineral density (BMD) have been reported to be lower in Asian than in Caucasian adults. To determine if racial differences in bone mass are present in younger subjects and whether they reflect differences in estimated volumetric bone density or in bone size, we compared measurements of bone mineral in healthy young Asian- and Caucasian-American males and females. Bone mineral was measured at the lumbar spine (L2-L4), femoral neck (FN), and whole body (WB) by dual-energy X-ray absorptiometry (DXA) in 99 Asians (49 females, 50 males) and 103 Caucasians (54 females, 49 males) ages 9-26 years. Results were expressed as BMC, BMD, and apparent density (BMAD), an estimate of volumetric bone density that reduces the effect of bone size. Subjects were compared on the basis of chronological age as well as by Tanner stage to correct for potential differences in the timing of puberty. Habitual dietary intake and physical activity were also assessed and correlated with bone mineral. The Asian and Caucasian cohorts differed in body size, diet, and physical activity. Asian females were shorter than the Caucasian females at all stages of puberty and weighed less at pre-/early puberty (p < 0.05). Asian males were older than Caucasians at midpuberty (p < 0.01) and weighed less than the Caucasian males at pubertal maturity (p = 0.001). Asian youths also consumed less calcium and reported less weight-bearing activity. Racial differences were most apparent when comparing BMC data. Asian males had greater spine BMC at midpuberty and lower WB BMC at maturity (p < 0.05). Asian females had lower FN BMC through midpuberty and lower WB BMC in pre-/early puberty (p < 0.05). WB BMD and WB BMC/height values were significantly lower in mature Asian versus Caucasian males. No significant racial differences in BMAD were observed. Multivariate regression analysis indicated that the differences in BMD and BMAD between Asian and Caucasian subjects were largely attributable to differences in weight and pubertal stage, and, at the FN, in weight-bearing activity. Further, the explanatory variables were less strongly associated with BMAD than with BMD. In summary, no significant differences in BMD were found between Asian and Caucasian youths through midpuberty; however, WB BMD and WB BMC/height values were lower in Asian males at sexual maturity. We conclude that observed differences in bone mineral between Asians and Caucasians may be partially attributed to the smaller bone size of Asians.

Absorptiometry, Photon↗
PubMed1996

The presence of a polymorphism at the translation initiation site of the vitamin D receptor gene is associated with low bone mineral density in postmenopausal Mexican-American women.

We examined the association of bone mineral density (BMD) with a polymorphism in the gene encoding the vitamin D receptor (VDR) that causes a change in the predicted protein sequence. The polymorphism results from a C-to-T transition and creates an initiation codon (ATG) three codons proximal to a downstream start site. The polymorphism can be defined by a restriction fragment length polymorphism (RFLP) using the restriction endonuclease FokI. The presence of a FokI site, designated f, allows protein translation to initiate from the first ATG. The allele lacking the site (designated F), initiates from a second ATG site. Thus, translation products from these alleles are predicted to differ by three amino acids with the f variant elongated. In a group of 100 postmenopausal Mexican-American Caucasian women, subjects with the ff genotype (15% of the study population) had a 12.8% lower BMD at the lumbar spine than FF subjects (37% of the population) (p = 0.01). Heterozygote (Ff) subjects (48% of the population) had an intermediate BMD. This association between BMD and genotype was not apparent at the femoral neck or forearm. Over a 2-year follow-up period, a decrease in BMD at the femoral neck was greater in ff compared with FF subjects (-4.7% vs. -0.5%, p = 0.005). This trend was not apparent at the lumbar spine or forearm. There were no differences between genotype groups in measurements of 25-hydroxyvitamin D (25(OH)D), calcitriol, parathyroid hormone (PTH), osteocalcin, or urinary pyridinolines. We conclude that the FokI polymorphism of the VDR gene correlates significantly with decreased BMD at the lumbar spine and with an increased rate of bone loss at the hip in ff subjects. We emphasize that these initial data should be interpreted with caution but that the utility of this polymorphism as a genetic marker to determine BMD and osteoporosis risk warrants further study in larger populations with subjects of diverse ethnic backgrounds.

Aged↗
PubMed1996

High-dose melphalan followed by autograft employing non-cryopreserved peripheral blood progenitor cells in children.

High-dose chemotherapy followed by autologous bone marrow transplantation (ABMT) enables dose escalation in the treatment of childhood malignancies. Here we report our experience of using peripheral blood progenitor cells (PBPC) to restore haematopoiesis in five children using a simple cell mobilising regime and non-cryopreservation of the harvests. Cells were mobilised using cyclophosphamide and granulocyte colony stimulating factor. Each patient underwent only two leukaphereses, the product being stored before use at 4 degrees C. Successful autologous PBPC transplantation was achieved with melphalan conditioning chemotherapy and re-infusion of the total progenitor cell product. No colony stimulating factors were administered after transplantation. The median numbers of mononuclear cells collected per patient was 10.0 x 10(8)/kg (range 8.13-19.44) and CFU-GM 57.6 x 10(4)/kg (range 10.4-178.85). All patients subsequently engrafted with the median number of days to a neutrophil count > 0.5 x 10(9)/l being 11 (range 10-16), and to a platelet count > 50 x 10(9)/l being 14 (range 12-31). The median number of in-patient days was only 20 (range 19-30). The median demand for blood was 2 units (range 1-2), and platelets 4 units (range 2-28). Usage of systemic antimicrobials and intravenous feeding was also low. Using this simple strategy, collection and transplantation of autologous progenitor cells can be a straightforward procedure in children. It is possible that this could enable dose escalation in some poor prognosis paediatric tumours.

Adolescent↗
PubMed1996

Body mass is the primary determinant of midfemoral bone acquisition during adolescent growth.

To study the determinants of bone mass and structure during adolescence, we analyzed the femoral mid-diaphysis of 375 healthy adolescents and young adults, ages 9-26 years, from four ethnic cohorts (African-American, Asian-American, Caucasian, and Hispanic). Whole-body dual-energy X-ray absorptiometry (DXA) scans were used to determine diaphyseal length and mid-diaphyseal diameter of the left femur, as well as linear bone mineral content (BMCL) of a region at the mid-diaphysis. Cross-sectional geometric properties were estimated and used to calculate two structural strength indicators: the section modulus and the whole bone strength index. When the relationships between the bone measurements and age, pubertal group, height, or body mass were evaluated, all cross-sectional femoral measures correlated most strongly with body mass. Multiple regressions accounting for gender and ethnicity provided little additional predictive value over the simple regressions with body mass alone. Furthermore, accounting for all developmental parameters (age, pubertal group, body mass, lean body mass, calcium intake, physical activity level) as well as ethnicity and gender in a single saturated model also did not generally significantly improve the predictive results achieved using only body mass. Our results indicate that increases in midfemoral bone mass and cross-sectional properties during adolescence are primarily related to increases in mechanical loading as reflected by body mass.

Adolescent↗