Pubertal development in obese children and adolescents

A changing pattern of childhood BMI growth during the 20th century: 70 y of data from the Fels Longitudinal Study

BACKGROUND

The BMI distribution shifted upward in the United States between the 1960s and the 1990s, but little is known about secular trends in the pattern of BMI growth, particularly earlier in the century and early in childhood.

OBJECTIVE

The objective was to examine differences in BMI growth in children born in 1929-1999.

DESIGN

BMI curves from ages 2 to 18 y were produced for 855 European-American children in the Fels Longitudinal Study born in 1929-1953, 1954-1972, and 1973-1999. Age (A(min)) and BMI (BMI(min)) at adiposity rebound and age (AV(max)), BMI (BMIV(max)), and velocity (V(max)) at maximum velocity were derived; multivariable regression was used to examine whether maternal BMI, infant weight gain, and other covariates mediated the cohort effects on these traits.

RESULTS

BMI curves showed that children born in 1973-1999 had the lowest BMI values until age 5 y but had the largest values from age 8 y onward. In adjusted models, boys and girls born in 1973-1999 had a 0.15-kg/m(2) per year faster V(max) and a 1-kg/m(2) higher BMIV(max) than did children of the same sex born in 1929-1953, and girls had a 0.8-y earlier A(min) (P < 0.01). Maternal BMI and infant weight gain were associated with an obesity-prone pattern of BMI growth but did not account for the observed trends.

CONCLUSIONS

Shifts in the BMI growth rate around the time of pubertal initiation were apparent starting after 1973. The BMI growth curve did not increase monotonically over time; rather, children born during the obesity epidemic were characterized by lower BMI values before the adiposity rebound and by rapid subsequent BMI gain.

Knee extension strength in obese and nonobese male adolescents

The aim of the present study was to compare "absolute" and "relative" knee extension strength between obese and nonobese adolescents. Ten nonobese and 12 severely obese adolescent boys of similar chronological age, maturity status, and height were compared. Total body and regional soft tissue composition were determined using dual-energy X-ray absorptiometry (DXA). Knee extensors maximum voluntary contraction (MVC) torque was measured using an isometric dynamometer at a knee angle of 60° (0° is full extension). Absolute MVC torque was significantly higher in obese adolescents than in controls. However, although MVC torque expressed per unit of body mass was found to be significantly lower in obese adolescent boys, no significant difference in MVC torque was found between groups when normalized to fat-free mass. Conversely, when correcting for thigh lean mass and estimated thigh muscle mass, MVC torque was significantly higher in the obese group (17.9% and 22.2%, respectively; P <0.05). To conclude, our sample of obese adolescent boys had higher absolute and relative knee extension strength than our nonobese controls. However, further studies are required to ascertain whether or not relative strength, measured with more accurate in vivo methods such as magnetic resonance imaging, is higher in obese adolescents than in nonobese controls.

Patterns of linear growth and skeletal maturation from birth to 18 years of age in overweight young adults

OBJECTIVE

To estimate differences in skeletal maturity and stature from birth to age 18 years between individuals who are overweight vs normal weight in young adulthood.

PATIENTS AND METHODS

Weight, length and height, and relative skeletal age (skeletal-chronological age) were assessed annually from birth to age 18 years in 521 subjects (255 women) in the Fels Longitudinal Study who were overweight or obese (body mass index (BMI) >25 kg m(-2), n=131) or normal weight (n=390) in young adulthood (18-30 years). Generalized estimating equations were used to test for skeletal maturity and stature differences by young adult BMI status.

RESULTS

Differences in height increased during puberty, being significant for girls at ages 10 to 12 years, and for boys at ages 11 to 13 years (P-values<0.001), with overweight or obese adults being ∼3 cm taller at those ages than normal weight adults. These differences then diminished so that by age 18 years, overweight or obese adults were not significantly different in stature to their normal weight peers. Differences in skeletal maturity were similar, but more pervasive; overweight or obese adults were more skeletally advanced throughout childhood. Skeletal maturity differences peaked at chronological age 12 in boys and 14 in girls (P-values<0.001), with overweight or obese adults being ∼1 year more advanced than normal weight adults.

CONCLUSIONS

This descriptive study is the first to track advanced skeletal maturity and linear growth acceleration throughout infancy, childhood and adolescence in individuals who become overweight, showing that differences occur primarily around the time of the pubertal growth spurt. Increased BMI in children on a path to becoming overweight adults precedes an advancement in skeletal development and subsequently tall stature during puberty. Further work is required to assess the predictive value of accelerated pubertal height growth for assessing obesity risk in a variety of populations.

Premature adrenarche: novel lessons from early onset androgen excess

Adrenarche reflects the maturation of the adrenal zona reticularis resulting in increased secretion of the adrenal androgen precursor DHEA and its sulphate ester DHEAS. Premature adrenarche (PA) is defined by increased levels of DHEA and DHEAS before the age of 8 years in girls and 9 years in boys and the concurrent presence of signs of androgen action including adult-type body odour, oily skin and hair and pubic hair growth. PA is distinct from precocious puberty, which manifests with the development of secondary sexual characteristics including testicular growth and breast development. Idiopathic PA (IPA) has long been considered an extreme of normal variation, but emerging evidence links IPA to an increased risk of developing the metabolic syndrome (MS) and thus ultimately cardiovascular morbidity. Areas of controversy include the question whether IPA in girls is associated with a higher rate of progression to the polycystic ovary syndrome (PCOS) and whether low birth weight increases the risk of developing IPA. The recent discoveries of two novel monogenic causes of early onset androgen excess, apparent cortisone reductase deficiency and apparent DHEA sulphotransferase deficiency, support the notion that PA may represent a forerunner condition for PCOS. Future research including carefully designed longitudinal studies is required to address the apparent link between early onset androgen excess and the development of insulin resistance and the MS.

Obesity in children and adolescents: relationship to growth, pubarche, menarche, and voice break

OBJECTIVE

The relationships between obesity, pubertal development, and height are controversial. Therefore, we compared the prevalence of pubarche, menarche, and voice break between a large collective of obese and normal-weight children and adolescents aged 10-16 years.

METHODS

We assessed weight, height, pubarche, menarche, and voice break in 1383 obese German children and in 6615 children of a representative national German cohort aged 10-16 years. In all obese children, gonadotropins were determined and birth weight data were collected.

RESULTS

Independently of gender, the height standard deviation score (SDS) was significantly greater (0.3-1.0) in obese children <14 years compared to the reference cohort. Independently of age, the percentage of obese boys with pubarche was significantly lower compared to age-matched normal-weight boys. In girls <13 years, the prevalence of obese girls with pubarche was significantly lower compared to age-matched normal-weight girls. In boys > or =11 years, the percentage of obese boys with change of voice was significantly lower compared to age-matched normal-weight boys. In girls > or =11 years, the prevalence of obese girls with menarche was significantly lower compared to age-matched normal-weight girls. Birth weight had no impact on pubarche in the obese children. Luteinizing hormone was > 0.3 IU/L in 86% of the children > or =10 years with pubarche.

CONCLUSIONS

Obese children are taller than normal-weight children up to the age of 14 years. Since obese children demonstrated pubarche, menarche, and voice break later than their normal-weight peers, the increase in height in obese children does not seem to be attributable to earlier onset of puberty.

Testosterone, obesity and insulin resistance in young males: evidence for an association between gonadal dysfunction and insulin resistance during puberty

OBJECTIVE

To assess the relationships among obesity, insulin sensitivity, and testosterone in pubertal boys.

PARTICIPANTS

This study included 20 lean, obese, and type 2 diabetic (T2DM) males, the majority of whom underwent a hyperinsulinemic-euglycemic clamp (n=16).

METHODS

Glucose disposal (M value), serum testosterone, and body mass index (BMI) z-score were measured. Differences in testosterone were evaluated by group (lean vs. obese vs. T2DM), while regression was performed to evaluate the relationships among testosterone, obesity and insulin sensitivity.

RESULTS

Controlling for Tanner stage, testosterone concentration was significantly lower in obese (p=0.02) and T2DM males (p=0.001) compared to lean males. Furthermore, M value was significantly associated with serum testosterone, even after controlling for BMI and Tanner stage.

CONCLUSIONS

These data suggest that obese adolescent boys have lower serum testosterone than controls of the same Tanner stage, and echo the data in adult males associating obesity and insulin resistance with hypogonadism.

Childhood obesity

Worldwide prevalence of childhood obesity has increased greatly during the past three decades. The increasing occurrence in children of disorders such as type 2 diabetes is believed to be a consequence of this obesity epidemic. Much progress has been made in understanding of the genetics and physiology of appetite control and from these advances, elucidation of the causes of some rare obesity syndromes. However, these rare disorders have so far taught us few lessons about prevention or reversal of obesity in most children. Calorie intake and activity recommendations need reassessment and improved quantification at a population level because of sedentary lifestyles of children nowadays. For individual treatment, currently recommended calorie prescriptions might be too conservative in view of evolving insight into the so-called energy gap. Although quality of research into both prevention and treatment has improved, high-quality multicentre trials with long-term follow-up are needed. Meanwhile, prevention and treatment approaches to increase energy expenditure and decrease intake should continue. Recent data suggest that the spiralling increase in childhood obesity prevalence might be abating; increased efforts should be made on all fronts to continue this potentially exciting trend.

Body mass index and timing of pubertal initiation in boys

OBJECTIVE

To examine the association between body mass index (BMI [calculated as weight in kilograms divided by height in meters squared]) and timing of pubertal onset in a population-based sample of US boys.

DESIGN

Longitudinal prospective study.

SETTING

Ten US sites that participated in the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development.

PARTICIPANTS

Of 705 boys initially enrolled in the study, information about height and weight measures and pubertal stage by age 11.5 years was available for 401 boys.

MAIN EXPOSURE

The BMI trajectory created from measured heights and weights at ages 2, 3, 4.5, 7, 9, 9.5, 10.5, and 11.5 years.

MAIN OUTCOME MEASURE

Onset of puberty at age 11.5 years as measured by Tanner genitalia staging.

RESULTS

Boys in the highest BMI trajectory (mean BMI z score at age 11.5 years, 1.84) had a greater relative risk of being prepubertal compared with boys in the lowest BMI trajectory (mean BMI z score at age 11.5 years, -0.76) (adjusted relative risk = 2.63; 95% confidence interval, 1.05-6.61; P = .04).

CONCLUSIONS

The relationship between body fat and timing of pubertal onset is not the same in boys as it is in girls. Further studies are needed to better understand the physiological link between body fat and timing of pubertal onset in both sexes.

Genetic variation of FTO and TCF7L2 in premature adrenarche

Premature adrenarche (PA) has been associated with increased body mass index. Our aim was to determine whether the obesity-associated variant at fat mass and obesity gene (FTO) is more frequent in PA subjects. Furthermore, we hypothesized that altered Wnt signaling due to genetic variants at transcription factor 7-like 2 (TCF7L2) could play a role in the polygenic pathogenesis of PA. We genotyped polymorphisms at FTO rs9939609 and at TCF7L2 rs7903146 and rs12255372 in 73 Finnish white prepubertal children with PA and in 97 age- and sex-matched healthy controls. In addition, we investigated the associations of these genetic variations with weight, height, circulating adrenocortical hormone levels, glucose metabolism, lipid profile, and blood pressure. The differences in the minor allele frequencies (MAFs) of rs9939609, rs7903146, and rs12255372 were not statistically significant between the PA and control groups (difference in MAFs [95% confidence interval]: -0.06 [-0.18, 0.05], 0.04 [-0.05, 0.12], and 0.01 [-0.07, 0.10]; P = .3, .4, and .8, respectively). However, the risk allele at TCF7L2 rs7903146 was more frequent in PA subjects than in controls when we restricted the analysis to the subjects with lower weight-for-height than the median of the PA subjects (weight-for-height <108%, corresponding body mass index SD score <0.79; difference in MAFs [95% confidence interval]: 0.12 [-0.001, 0.23]; P = .038). Risk variant at FTO rs9939609 associated with higher weight-for-height in the healthy children (P = .001). In conclusion, the minor variant at FTO rs9939609 seems to play no major role in the increased weight-for-height of PA subjects; but the risk allele at TCF7L2 rs7903146 may have a role in the pathogenesis of PA in lean subjects.

Primary testicular dysfunction is a major contributor to abnormal pubertal development in males with Prader-Willi syndrome

BACKGROUND

Recent studies challenge the assumption that hypogonadism in Prader-Willi syndrome (PWS) is due only to hypothalamic dysfunction.

OBJECTIVES

The aims of the study were to characterize sexual development and reproductive hormones in PWS males and investigate the etiology of hypogonadism.

METHODS

Physical examination and blood sampling were performed on 37 PWS males, ages 4 months to 32 yr.

RESULTS

All had a history of undescended testes; age at orchiopexy ranged from 2 months to 6 yr. Pubertal signs were variable, but none achieved full genital development. Anti-Mullerian hormone (AMH) levels in PWS boys were near the lower limits of normal, decreasing from 44.4 +/- 17.8 ng/ml (mean +/- sd) in young children to 5.9 +/- 4.7 ng/ml in adolescents, similar to normal males. In contrast, inhibin B was consistently low (27.1 +/- 36.1 pg/ml) or undetectable in all age groups. In adult males, FSH levels were high (20.3 +/- 18.3 IU/liter), LH levels were normal (4.2 +/- 4.3 IU/liter), and testosterone levels were low (1.87 +/- 1.17 ng/ml). Only two adults had severe hypogonadotropic hypogonadism with undetectable levels of LH and FSH and high AMH levels (34.9 and 36.7 ng/ml), unlike the other nine adults with AMH levels 2.6 +/- 2.1 ng/ml. Androstenedione (1.06 +/- 0.30 ng/ml) and DHEAS (281.1 +/- 143.6 microg/dl) in adult PWS were normal.

CONCLUSIONS

Pubertal development in PWS is characterized by normal adrenarche, variable hypothalamic dysfunction, and hypogonadism due to a unique testicular defect. Primary testicular dysfunction is a major component of hypogonadism in PWS.

Androgen receptor gene CAG repeat polymorphism and X-chromosome inactivation in children with premature adrenarche

CONTEXT

There is variation in the adrenal androgen levels and clinical findings of children with premature adrenarche (PA).

OBJECTIVES

We hypothesized that androgen sensitivity, indicated by the length of CAG repeat in the X-chromosomal androgen receptor (AR) gene has a role in the polygenic pathogenesis of PA.

DESIGN AND PATIENTS

We performed a cross-sectional association study among 73 Finnish Caucasian children with PA (10 boys and 63 girls) and 97 age- and gender-matched healthy controls (18 boys and 79 girls).

MAIN OUTCOME MEASURES

AR gene methylation-weighted CAG(n)(mwCAG(n)) via CAG(n) length and X-chromosome inactivation analysis and clinical phenotype were determined.

SETTING

The study took place at a university hospital.

RESULTS

PA subjects had significantly shorter mwCAG(n) than controls [mean difference (95% confidence interval); 0.76 (0.14-1.38); P = 0.017]. AR gene mwCAG(n) did not correlate with androgen or SHBG levels in either group. In children with PA, mwCAG(n) correlated positively with body mass index (BMI) (tau = 0.19; P = 0.02). The mean of mwCAG(n) was significantly shorter in PA children with lower BMI compared with PA children with higher BMI [BMI sd score < 0.79, n = 35, vs. BMI sd score > 0.79, n = 36; 1.13 (0.38-1.87), P = 0.004] and in PA children with lower BMI compared with healthy children with same BMI (P = 0.004).

CONCLUSIONS

The AR gene CAG(n) polymorphism may have a significant role in the pathogenesis of PA, especially in lean children.