Bone metabolism markers predict increase in bone mass, height and sitting height during puberty depending on the VDR Fok1 genotype.

OBJECTIVES: Longitudinal growth and bone mass accumulation are two important phenomena during puberty, resulting in attainment of peak bone mass (PBM) and final height. They are thought to be under strong genetic control, with the vitamin D receptor (VDR) gene being among the candidate genes. Bone metabolism markers are reported to be good predictors of longitudinal growth and bone mass increase. The purpose of this longitudinal study was to evaluate whether bone metabolism markers predict bone mass and height increase differently according to Fok1 VDR genotype throughout puberty in healthy adolescents. PATIENTS AND MEASUREMENTS: At the start of the study 130 girls were aged 10.8 (range 8.5-12.8) years and 125 boys were aged 11.8 (range 9.4-14.6) years at the first visit. Markers of bone formation and bone resorption were measured at the first visit, as well as height and sitting height (SH), and bone mineral content (BMC) of the lumbar spine, femur, arm and total body. All measurements were repeated after 2 years. RESULTS: A higher BMC of the femur, distal arm and total body was found in ff boys at the first visit, which was not related to higher levels of bone metabolism markers in this group. In girls, no differences between genotypes were seen in BMC (increase). However, concentrations of markers of bone formation [alkaline phosphatase (AP), bone-specific alkaline phosphatase (BAP), procollagen aminoterminal propeptide (PINP)] and bone resorption [type I carboxyterminal telopeptide (ICTP)] were higher in ff girls. Regression coefficients between bone metabolism markers and bone mass increase differed according to genotype and sex. A similar pattern was found for height and SH (increase), the latter as a representative of growth of the axial skeleton, mainly consisting of cancellous bone. CONCLUSIONS: Our data suggest that the predicting capacities of bone metabolism markers on bone mass (increase), height and SH (increase) are genotype dependent. Their use as predictors of final height or PBM therefore remains questionable without knowing the genotype.

Reproducibility of bone mineral density measurement in daily practice.

BACKGROUND: Bone mineral density (BMD) measurements are frequently performed repeatedly for each patient. Subsequent BMD measurements allow reproducibility to be assessed. OBJECTIVE: To examine the reproducibility of BMD by dual energy x ray absorptiometry (DXA) and to investigate the practical value of different measures of reproducibility in a group of postmenopausal women. METHODS: Ninety five women, mean age 59.9 years, underwent two subsequent BMD measurements of spine and hip. Reproducibility was expressed as smallest detectable difference (SDD), coefficient of variation (CV), and intraclass correlation coefficient (ICC). Sources of variation were investigated by multilevel analysis. RESULTS: The median interval between measurements was 0 days (range 0-45). The mean difference (SD) between the measurements (g/cm(2)) was -0.001 (0.02) and -0.0004 (0.02) at L1-4 and the total hip, respectively. At L1-4 and the total hip, SDD (g/cm(2)) was +/-0.05 and +/-0.04 and CV (%) was 1.92 and 1.59, respectively. The ICC at spine and hip was 0.99. CONCLUSIONS: Reproducibility in the postmenopausal women studied was good. In a repeated DXA scan a BMD change exceeding 2 radical 2CV (%), the least significant change (LSC), or the SDD should be regarded as significant. Use of the SDD is preferable to use of the CV and LSC (%) because of its independence from BMD and its expression in absolute units. Expressed as SDD, a BMD change of at least +/-0.05 g/cm(2) at L1-4 and +/-0.04 g/cm(2) at the total hip should be considered significant.

Bone metabolism markers and bone mass in healthy pubertal boys and girls.

OBJECTIVE: During puberty, bone growth and mineralization as well as bone turnover increase dramatically. The relation between height velocity and bone turnover is already known, but there are few studies in which both bone metabolism markers and bone mass throughout puberty have been measured. DESIGN: Semi-longitudinal study. In 155 healthy boys (12.0 +/- 1.5 years; range 8.8-15.7 years) and 151 healthy girls (11.2 +/- 1.6 years; range 8.2-14.0 years) markers of bone formation and bone resorption were measured as well as sex steroids, IGF-1 and IGF-BP3, together with bone mineral content (BMC) and bone mineral density (BMD) of the lumbar spine, femur and total body during puberty. All bone measurements were repeated after 1 year. RESULTS: BMC and BMD increased throughout puberty in both sexes. Bone turnover markers increased significantly until maximum values were reached at stage G4 in boys and stage B3 in girls. Height velocity (HV) had a similar changing pattern. Sex steroids and IGF-1 increased and reached adult values at pubertal stage 4. The correlations between bone metabolism markers and BMC were highly significant in boys, while correlations between bone metabolism markers and the increase in BMC over 1 year were significant in both sexes, as was observed for the correlations with HV. CONCLUSIONS: Our data suggest that bone metabolism markers are good predictors of bone mass in boys and of bone mass increase in both sexes. In early puberty, sex steroids stimulate the pubertal growth spurt in conjunction with GH and IGF-1. The fast increase in height gives rise to an increase in bone turnover and bone mineral apposition. It is known that at the end of puberty high levels of oestradiol inhibit chondrocyte proliferation. This leads to a decline in height velocity and bone turnover. Bone mass still increases under the influence of sex steroids and IGF-1. The data in our study confirm previous reports that markers of bone turnover relate positively to height velocity.

Pubertal maturation characteristics and the rate of bone mass development longitudinally toward menarche.

To assess risks for osteoporosis and to compare bone mass in different groups of healthy children or children with diseases, it is important to have knowledge of their sexual maturation status during puberty. The aim of our study was to evaluate bone mass formation longitudinally in relation to pubertal maturation characteristics in healthy white girls. We investigated the bone mineral content (BMC) and the bone mineral density (BMD) at different skeletal sites in 151 girls with increasing pubertal stages in relation with their chronological age and with an early or late onset of puberty or menarche and with a slow or fast maturation. Bone mass was measured at the onset of puberty, during puberty, and at menarche. We conclude the following: (1) from midpuberty to menarche, the increase in bone mass formation is highest at all skeletal sites in white girls; (2) early mature girls at the onset of puberty have slightly but definitely lower bone masses at all skeletal sites and at all pubertal stages than late mature girls, whereas the average bone mass formation from the onset of puberty to menarche is similar in both groups; (3) girls with a slow rate of pubertal maturation have lower bone mass values 2 years after the onset of puberty, but at menarche bone mass is similar compared with fast maturers; and (4) it cannot be confirmed that there is an effect of menarcheal age on bone mass values at menarche.

Hormonal determinants of pubertal growth.

Pubertal growth results from increased sex steroid and growth hormone (GH) secretion. Estrogens appear to play an important role in the regulation of pubertal growth in both girls and boys. In girls, however, estrogens cannot be the only sex steroids responsible for pubertal growth, as exogenous estrogens do not initiate a complete growth spurt. We therefore investigated the levels of the different sex steroids and GH, and related them to pubertal growth. In addition, we studied the process of bone maturation and mineralization during this period. Levels of both estrogens and androgens were found to increase at the start of the female pubertal growth spurt, and it was demonstrated that height velocity is related to levels of GH, estradiol and androstenedione, but not dehydroepiandrosterone sulfate. In boys, GH, testosterone and estradiol increased at the time of peak height velocity. Bone mineralization increased as puberty began, and was associated with the increase in height velocity. Osteocalcin, a marker of bone formation, declined when height velocity decreased, although bone maturation progressed at a steady rate. We conclude, therefore, that in girls, the concerted actions of estradiol, GH and androstenedione play a role in the pubertal growth spurt, whereas in boys this role is fulfilled by testosterone, GH and estradiol. During puberty, an advanced rate of bone maturation with respect to cross-sectional standards is a physiological phenomenon.