Simple fasting methods to assess insulin sensitivity in childhood

The 'gold standard' techniques used to measure insulin sensitivity in children are the hyperinsulinaemic-euglycaemic clamp and Bergman's minimal model. Although precise, these techniques are complex, invasive and time consuming. Alternative indirect measures of insulin sensitivity have been developed that utilize fasting glucose and insulin data in algorithms or computer programs. These methods include homeostatic model assessment (HOMA), the quantitative insulin sensitivity check index (QUICKI) and the glucose to insulin ratio (G:I). Each of these three fasting techniques has been developed and validated in adults, with little or no validation in children. Increasingly, HOMA and QUICKI are being used in childhood studies to assess insulin sensitivity. In a group of 79 pre-pubertal children, we found that the correlation between the minimal model and RHOMA (r = -0.4) was no better than that between the minimal model and fasting insulin (r = 0.4), with an even weaker correlation between the minimal model and QUICKI (r = 0.2). In addition, neither HOMA nor QUICKI were able to detect a reduction in insulin sensitivity with obesity or during growth hormone therapy, unlike the minimal model. In children with normal glucose levels, neither HOMA nor QUICKI was superior to fasting insulin. Validation of the derivation formulae for these methods in children is needed before they are more widely used. The potential benefits of these simple fasting techniques is that they are useful in large field studies. However, if the study groups are small or longitudinal changes in insulin sensitivity are sought, more precise techniques such as the clamp or minimal model should be used.

Insulin sensitivity in people born pre-term, with low or very low birth weight and small for gestational age

Evidence has accumulated that small for gestational age (SGA) children have long-term adult health consequences including obesity, Type 2 diabetes mellitus, hypertension, coronary artery disease and stroke. This increased risk of later adult disease is likely a consequence of an early, persistent reduction in insulin sensitivity. The SGA children and adults studied were predominantly at term gestation, and it appears that prematurity also leads to insulin resistance with possibly similar health consequences for later life. Both term SGA and premature children have an abnormal early environment: one in utero and one post-natally. Parallels are made among those born SGA at term or premature to show the potential importance of maternal factors, the intrauterine milieu, including nutrient supply and intake in fetal and early newborn life. It is possible that manipulation of these factors during early neonatal life in premature babies could lead to normalisation of insulin sensitivity. To confirm this hypothesis, further studies are needed to better understand the pathophysiological mechanisms leading to reduced insulin sensitivity and confirm that prematurity is linked with similar long-term health consequences as being born SGA.

Evaluation of the buserelin stimulation test in diagnosing gonadotropin deficiency in males with delayed puberty

OBJECTIVE

To assess the efficacy of the gonadotropin-releasing hormone (GnRH) agonist buserelin in a stimulated gonadotropin test for the investigation of delayed puberty in males.

STUDY DESIGN

Prepubertal males (n = 31; age range, 10.3 to 17.2 years) were studied; buserelin (100 microg) was administered subcutaneously, with blood sampling at 0 and 4 hours for serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH). At follow-up (mean, 4.2 years), 8/31 (26%) failed to progress into puberty, constituting hypogonadotropic hypogonadism (HH), but 23/31 (74%) had testicular enlargement (> or =8 mL) consistent with a normal hypothalamic-pituitary-gonadal (HPG) axis.

RESULTS

Stimulated serum LH response to buserelin was lower in males with HH (mean +/- standard error under the mean for HH, 1.4 +/- 0.5 U/L, compared with a normal HPG axis of 17.4 +/- 2.0 U/L; P < .0001). Stimulated serum FSH response was nondiscriminatory (HH, 7.7 +/- 2.2 U/L; normal HPG axis, 11.5 +/- 1.6 U/L; P = .27). All males with HH had a stimulated serum LH level <5 U/L, whereas only 1/23 with a normal HPG axis had a stimulated serum LH below this level. Using this value as the criterion for diagnosing HH, the buserelin stimulation test yielded a sensitivity of 100%, specificity of 96%, and positive predictive value of 89%.

CONCLUSIONS

The buserelin stimulation test is a highly specific and sensitive GnRH agonist test for the investigation of males with delayed puberty.

Fetal origins of adult disease: a paediatric perspective

Prepubertal children born SGA or VLBW premature exhibit marked insulin resistance. There are similarities between SGA and VLBW children in that both are exposed to sub-optimal environments that encompass undernutrition and/or malnutrition during the equivalent of the last trimester of pregnancy. Although both SGA and VLBW groups fail to reach genetic height potential and are recognized causes of short stature in childhood, there are differences between the groups with respect to the growth hormone and IGF-I axis.SGA children have elevated IGFI levels, possibly due to either hyperinsulinism or partial IGF-I resistance, whereas VLBW children have low IGF-I and IGFBP-3 levels suggestive of GH resistance. Thus the nature and timing of the early insult may lead to discordant changes to the metabolic and endocrine axes.IVF children are taller with increased IGF I, IGF II and IGFBP3 expression. These changes could be due to alterations in the environment of the periconceptual embryo resulting in changes in imprinting of genes involved in growth and development. The phenotypic, endocrine and metabolic consequences of alterations in the periconceptual, fetal and early neonatal periods is an area of intense investigation. Future research in this field is likely to focus on the mechanisms through which environmental changes lead to these programmed effects.

Neonatal leptin treatment reverses developmental programming

An adverse prenatal environment may induce long-term metabolic consequences, in particular obesity and insulin resistance. Although the mechanisms are unclear, this programming has generally been considered an irreversible change in developmental trajectory. Adult offspring of rats subjected to undernutrition during pregnancy develop obesity, hyperinsulinemia, and hyperleptinemia, especially in the presence of a high-fat diet. Reduced locomotor activity and hyperphagia contribute to the increased fat mass. Using this model of maternal undernutrition, we investigated the effects of neonatal leptin treatment on the metabolic phenotype of adult female offspring. Leptin treatment (rec-rat leptin, 2.5 microg/g.d, sc) from postnatal d 3-13 resulted in a transient slowing of neonatal weight gain, particularly in programmed offspring, and normalized caloric intake, locomotor activity, body weight, fat mass, and fasting plasma glucose, insulin, and leptin concentrations in programmed offspring in adult life in contrast to saline-treated offspring of undernourished mothers who developed all these features on a high-fat diet. Neonatal leptin had no demonstrable effects on the adult offspring of normally fed mothers. This study suggests that developmental metabolic programming is potentially reversible by an intervention late in the phase of developmental plasticity. The complete normalization of the programmed phenotype by neonatal leptin treatment implies that leptin has effects that reverse the prenatal adaptations resulting from relative fetal undernutrition.

Reduced insulin sensitivity and the presence of cardiovascular risk factors in short prepubertal children born small for gestational age (SGA)

BACKGROUND

Epidemiological studies have shown that the metabolic syndrome, a combination of type 2 diabetes mellitus, hypertension, dyslipidaemia and a high body mass index (BMI), occurs more frequently among adults who were born with a low birth weight. Because insulin is thought to play a key role in the pathogenesis of this syndrome we investigated insulin sensitivity and risk factors for cardiovascular disease in short prepubertal children born small for gestational age (SGA).

PATIENTS AND METHODS

Frequently sampled intravenous glucose tolerance tests (FSIGT) were performed in 28 short prepubertal children born SGA. Short stature was defined as a height < -2SD. SGA was defined as a birth length and/or a birth weight for gestational age < -2SD. Twelve short children born appropriate for gestational age (AGA) were used as controls for the FSIGT's results only. AGA was defined as a birth weight and/or birth length for gestational age > -2SD. In short SGA children, blood pressure (BP), fasting levels of serum free fatty acids (FFA), triglycerides (TG), total cholesterol (TC), high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) were measured and compared to reference values.

RESULTS

Mean insulin sensitivity (Si) level in short SGA children was significantly reduced to 38% of the mean Si level measured in short AGA controls (P = 0.004). Mean acute insulin response (AIR) was significantly higher in SGA children compared to short AGA controls (P < 0.001). Differences in Si and AIR between the two groups remained significant after adjusting for age and BMI (P < 0.001 and P = 0.003, respectively). The mean (SD) systolic BP SDS was 1.3 (1,1), being significantly higher than zero. Mean fasting serum levels of FFA, TC, TG, HDL and LDL were all within the normal range. However, 6 of the 28 SGA children had serum FFA levels above the normal range. Cardiovascular risk factors could statistically be represented in two clusters. Both clusters played a significant role in the development of insulin insensitivity (1/Si).

CONCLUSION

Although the metabolic syndrome has been described in adulthood, our study showed that risk factors for the development of type 2 diabetes mellitus and cardiovascular disease are already present during childhood in short prepubertal children born SGA, suggesting a pretype 2 diabetes mellitus phenotype.

Premature birth and later insulin resistance

BACKGROUND

Term infants who are small for gestational age appear prone to the development of insulin resistance during childhood. We hypothesized that insulin resistance, a marker of type 2 diabetes mellitus, would be prevalent among children who had been born prematurely, irrespective of whether they were appropriate for gestational age or small for gestational age.

METHODS

Seventy-two healthy prepubertal children 4 to 10 years of age were studied: 50 who had been born prematurely (32 weeks' gestation or less), including 38 with a birth weight that was appropriate for gestational age (above the 10th percentile) and 12 with a birth weight that was low (i.e., who were small) for gestational age, and 22 control subjects (at least 37 weeks' gestation, with a birth weight above the 10th percentile). Insulin sensitivity was measured with the use of paired insulin and glucose data obtained by frequent measurements during intravenous glucose-tolerance tests.

RESULTS

Children who had been born prematurely, whether their weight was appropriate or low for gestational age, had an isolated reduction in insulin sensitivity as compared with controls (appropriate-for-gestational-age group, 14.2x10(-4) per minute per milliunit per liter [95 percent confidence interval, 11.5 to 16.2]; small-for-gestational-age group, 12.9x10(-4) per minute per milliunit per liter [95 percent confidence interval, 9.7 to 17.4]; and control group, 21.6x10(-4) per minute per milliunit per liter [95 percent confidence interval, 17.1 to 27.4]; P=0.002). There were no significant differences in insulin sensitivity between the two premature groups (P=0.80). As compared with controls, both groups of premature children had a compensatory increase in acute insulin release (appropriate-for-gestational-age group, 2002 pmol per liter [95 percent confidence interval, 1434 to 2432] [corrected]; small-for-gestational-age group, 2253 pmol per liter [95 percent confidence interval, 1622 to 3128]; and control group, 1148 pmol per liter [95 percent confidence interval, 875 to 1500]; P<0.001).

CONCLUSIONS

Like children who were born at term but who were small for gestational age, children who were born prematurely have an isolated reduction in insulin sensitivity, which may be a risk factor for type 2 diabetes mellitus.

Growth hormone treatment in children: review of safety and efficacy

Since the advent of growth hormone (GH), the pediatric applications of GH therapy have expanded. Children with a wide variety of growth disorders have received GH treatment. The therapeutic effects and safety profile of GH in a number of pediatric conditions are reviewed, including GH deficiency (GHD), Turner syndrome, chronic renal failure, children born small for gestational age, Prader-Willi syndrome, juvenile chronic arthritis, and cystic fibrosis. GH therapy has been clearly shown to improve height velocity during childhood in a variety of pediatric conditions in which growth is compromised. There is now data that confirms GH treatment also improves final height in a number of diagnostic subgroups. Early initiation and individualization of GH treatment has the potential to normalize childhood growth in children with idiopathic GHD and enable them to achieve their genetic target height in a cost-effective manner. In children in whom GHD is not the main factor compromising growth, supra-physiological doses of GH have been shown to increase height velocity during childhood and final height. The development of predictive models for these conditions may allow further improvements in height outcome while maintaining an acceptable safety profile. Survivors of childhood malignancy, particularly those who have had craniospinal irradiation, represent a particularly challenging group. They appear to be less responsive to GH than children with idiopathic GHD and have a tendency to enter puberty at an earlier age. Both of these factors have a negative impact on their final height. Strategies that combine GH treatment with suppression of puberty using a gonadotropin releasing hormone analog may result in improved height outcomes. When children with GHD are treated with standard doses of GH there is a strong safety record. Adverse events during GH therapy are uncommon and often not drug related. Continued surveillance into adult life is crucial however, particularly in children receiving supra-physiological doses of GH or whose underlying condition increases their risk of adverse effects.

The endocrine consequences for very low birth weight premature infants

The aims of this study were: (1) to determine whether premature and small-for-gestational-age (SGA) children have alterations to the insulin-like growth factor (IGF)-IGF binding protein axis and (2) to evaluate growth in premature children. Three groups of children were evaluated: (i) premature children of </= 32 weeks gestation, which included appropriate-for-gestational-age (AGA) and small-for-gestational-age (SGA) subgroups; (ii) term children of >36 weeks gestation, which included AGA and SGA subgroups; and (iii) children born at term and AGA with normal childhood heights and weights. Fasting plasma IGF-I, insulin-like growth factor binding protein-3 (IGFBP-3), and IGF-II (all expressed as microgm/L) were drawn on available subjects. To examine the influence of SGA on the IGF-IGFBP axis, term SGA subjects were compared with term AGA subjects. To examine the influence of prematurity on the IGF-IGFBP axis, preterm SGA subjects were compared with term SGA subjects and preterm AGA subjects were compared with the normal-stature AGA controls. This ensured that groups of very similar stature and nutritional statuses were compared. Auxological data were available for 24 premature children, and biochemical data were available for 77 children, including the premature children. Across the height standard deviation score (SDS) range, premature children did not reach mid-parental height (MPH) SDS and were approximately 0.6 standard deviations (SDs) below the MPH SD (P < 0.0001). Plasma IGF-I and IGFBP-3 levels were higher in term SGA subjects compared with term AGA subjects (P < 0.001, respectively). Conversely, IGF-I and IGFBP-3 values were lower in the premature SGA subgroup compared with the premature AGA subgroup (P < 0.001 for both), and both were also lower in the premature AGA subgroup compared with the normal-statured AGA subgroup (P < 0.001 for both). IGF-II values were higher in the preterm group than in the term group (P < 0.001). In conclusion, very low birth weight (VLBW) children, regardless of whether they were AGA or SGA, have low plasma IGF-I and IGFBP-3 levels in mid-childhood, suggesting partial growth hormone (GH) resistance. Conversely, term SGA children have elevated plasma IGF-I and IGFBP-3 levels. When combined, premature birth plays a more dominant role than SGA on the IGF-IGF binding protein axis.

The metabolic consequences of prematurity

An association between low birth weight, commonly a reflection of an adverse in utero environment, and the subsequent development of diseases such as type 2 diabetes and hypertension in later life is now generally accepted - as is an association between an adverse perinatal environment and a permanent reduction in insulin sensitivity. This and other metabolic abnormalities have been demonstrated from childhood through to adulthood in subjects who were born full-term but small for gestational age (SGA). Less is known about children born prematurely into an adverse neonatal environment. We present data demonstrating that premature infants also have metabolic abnormalities similar to those observed in full-term, SGA children, and that these occur irrespective of whether the premature infants are SGA or appropriate for gestational age (AGA).

Insulin sensitivity in the offspring of women with type 1 and type 2 diabetes

OBJECTIVE

To determine if insulin sensitivity is altered in prepubertal offspring exposed to a diabetic intrauterine environment.

RESEARCH DESIGN AND METHODS

Fifteen control children, 17 offspring of type 1 diabetic women, and 10 offspring of type 2 diabetic women, aged between 5 and 10 years, underwent a frequently sampled intravenous glucose tolerance test (FSIGTT). Weight and height were measured, and body composition was calculated using bioelectrical impedance. Bergman's minimal model was applied to the glucose and insulin measurements to obtain values for insulin sensitivity (Si), acute insulin response (AIR), and glucose effectiveness (Sg).

RESULTS

Si was lowest in the offspring of type 2 diabetic mothers, and AIR was highest in this group, although neither of these changes reached significance (Si, P = 0.2, and AIR, P = 0.3). Offspring of type 2 diabetic mothers had higher BMI SD scores (P = 0.004) and percentage fat mass (P = 0.002) than the children in the other two groups. The BMI SD score and percentage fat mass in the subjects, as well as maternal insulin dose, were negatively correlated with offspring insulin sensitivity.

CONCLUSIONS

Intrauterine exposure to hyperglycemia by itself was not associated with alterations in glucose regulation in prepubertal offspring. Children of mothers with type 2 diabetes, however, were overweight, and they had a tendency for a reduced Si. The combined effect of genetic and postnatal environmental factors, rather than prenatal exposure to hyperglycemia, may place this group at risk for developing impaired glucose tolerance in later life.

Insulin resistance in healthy prepubertal twins

OBJECTIVES

To evaluate insulin sensitivity (S(I)) in prepubertal twins and to examine the relation to reduced birth weight, prematurity, and peroxisome proliferator-activated receptor-gamma (PPAR gamma) polymorphism.

STUDY DESIGN

Fifty twins (birth weight SDS, -0.7 +/- 0.2; gestation, 33.5 +/- 0.5 weeks; and body mass index SDS, -0.04 +/- 0.2) were studied at 8.2 +/- 0.3 years. S(I) was measured by Bergman's minimal model from a 90 minutes frequently sampled intravenous glucose test. Twenty control children (height SDS, -1.7 +/- 0.3; birth weight SDS, -0.3 +/- 0.2; and gestation of 39.2 +/- 0.7 weeks) were also evaluated at 7.0 +/- 0.4 years. The PPAR gamma T-variant polymorphism was evaluated in 41 twins. Values are expressed as mean +/- SEM, or 95% confidence intervals.

RESULTS

S(I) was reduced in twins compared with control subjects, (12.7 [11-15] versus 23.0 [16.8-31.4] 10(-4) min(-1) microU/mL, respectively, P=.005). The reduction in S(I) was independent of prematurity and birth weight and zygosity (P<.0001). There was no difference in S(I), even in twin pairs with >20% difference in birth weight (P=.9). The PPAR gamma heterozygote T-variant polymorphism was present in 7 of 41, with a further reduction in S(I) (P=.03) and a later gestation (P=.03). These twins also had increased fat mass (P=.02) but with similar fat free mass (P=.14).

CONCLUSIONS

Twin children, independent of prematurity or birth weight, had a marked reduction in S(I). To use twins as a model to study the fetal origins of adult diseases for glucose homeostasis is not valid.

Increasing prevalence of type 2 diabetes in adolescents

OBJECTIVE

The rising prevalence of obesity in childhood and adolescence in North America has been paralleled by the emergence of type 2 diabetes in the adolescent age group. We have examined trends in the prevalence of type 2 diabetes in adolescents attending a diabetes clinic in Auckland, New Zealand.

METHODS

Surveys of the prevalence of type 2 diabetes in attendees at the adolescent diabetes clinic at the Auckland Diabetes Centre were undertaken in 1996 and 2002. The proportion of type 2 diabetes in incident cases of diabetes diagnosed between these years was also calculated.

RESULTS

The prevalence of type 2 diabetes was 1.8% (2/110) in 1996, and 11.0% (18/163) in 2002 (P = 0.008). Type 2 diabetes accounted for 12.5% (6/48) of incident cases of diabetes in the years 1997-1999, and 35.7% (10/28) of cases in the years 2000-2001, indicating a sharp rise in the incidence (P = 0.017) between the two periods. At diagnosis the mean age of the type 2 diabetes subjects was 15 years and the mean body mass index 34.6 kg/m2. Risk factors for cardiovascular disease were common in the subjects with type 2 diabetes: 85% had dyslipidaemia, 58% had increased albumin excretion rates and 28% had systolic hypertension.

CONCLUSIONS

Obesity-related type 2 diabetes now accounts for a substantial proportion of newly recognized diabetes in the adolescent age group - and this proportion is escalating rapidly. Adverse cardiovascular risk factors are prevalent in this population. Public health measures to curtail the rise of obesity in childhood and adolescence are required urgently.

Insulin resistance is not due to persistently elevated serum tumor necrosis-alpha levels in small for gestational age, premature, or twin children

BACKGROUND

In pregnancies with small for gestational age (SGA) fetuses, elevated amniotic fluid tumor necrosis factor-alpha (TNF-alpha) levels have been reported. TNF-alpha has been shown to induce insulin resistance in rodents and humans. We hypothesized that an adverse fetal or early neonatal environment for SGA, twin, and premature children leads to persistently elevated TNF-alpha levels that induce insulin resistance in each of these groups.

METHODS

The study group consisted of 16 SGA, 14 premature, 53 twin subjects, and the control group of 40 normal subjects (10 short-stature and 30 normal-stature). All subjects were prepubertal and non-obese. Insulin sensitivity (S(I)) was measured in all but the normal-statured control subjects. Fasting plasma TNF-alpha and cortisol levels were measured in all subjects.

RESULTS

The study group had reduced S(I)[SGA 18.5 +/- 3, premature 17.8 +/- 2, twin 12.7 +/- 0.7 (x10(-4)/min/ microU/mL)] compared to the short normal control subjects (43 +/- 8 x 10(-4)/min/ microU/mL, p < 0.001). Plasma TNF-alpha levels were lower in the insulin-resistant study group when compared to the control group (2.9 +/- 0.1 vs. 5.0 +/- 0.2 pg/mL, p < 0.001). An association was present between reduced S(I) and low plasma TNF-alpha levels in the study group (p = 0.01, r = 0.4). Fasting plasma cortisol was lower in the study compared to the control group (266 +/- 16 vs. 341 +/- 28 nmol/L, p < 0.01) due to the influence of the twin study subgroup. There was no relationship between plasma cortisol and TNF-alpha levels (p = 0.3).

CONCLUSION

SGA, premature, and twin children are insulin resistant and have low plasma TNF-alpha and cortisol levels. We speculate that the mechanism leading to insulin resistance in these subjects is also suppressing plasma TNF-alpha and cortisol concentrations.

Evaluation of HOMA and QUICKI as measures of insulin sensitivity in prepubertal children

BACKGROUND

Simple fasting sample methods to measure insulin sensitivity (SI) such as homeostasis model assessment (HOMA) and quantitative insulin-sensitivity check index (QUICKI) have been widely promoted in adult studies but have not been formally evaluated in children. The aim of this study was to compare HOMA and QUICKI to the minimal model as measures of SI in prepubertal children.

METHOD

The study population consisted of twins (n = 44), premature (n = 17), small for gestational age (SGA) (15), and normal (n = 3) prepubertal children. The insulin-sensitivity index derived by the minimal model (SIMM) was calculated by the minimal model with plasma glucose and insulin data from a 90-min frequently sampled intravenous glucose test with tolbutamide. The HOMA resistance index (RHOMA) and QUICKI were calculated from fasting plasma glucose and insulin values.

RESULTS

The correlation between RHOMA and SIMM (r = -0.4, p < 0.001) was no better than that between fasting insulin and SIMM (r = -0.4, p < 0.001). QUICKI was poorly correlated with SIMM (r = 0.2, p = 0.02). The correlation between SIMM and RHOMA is largely confined to low SI values (< 10 x 10(-4)/min microU/mL.) In seven SGA subjects, the introduction of growth hormone treatment led to an expected fall in SIMM by 8.2 +/- 2.8 x 10(-4)/min microU/mL (p = 0.02) that was not detected by either RHOMA (p = 0.1) or QUICKI (p = 0.2). Similarly, SIMM values were lower in obese (n = 9) compared to non-obese subjects (p = 0.04); however, no difference was found between these two groups with either RHOMA (p = 0.21) or QUICKI (p = 0.8).

CONCLUSION

As measures of SI in prepubertal children, RHOMA is no better than fasting insulin and QUICKI, a poor measure. Neither RHOMA nor QUICKI was able to detect changes in SI induced by either obesity or growth hormone therapy.

Increased nocturnal blood pressure in healthy prepubertal twins

AIM

To compare ambulatory blood pressure monitoring (ABPM) in twin children to a published singleton population, and to examine the influence of birthweight and fasting plasma cortisol on blood pressure.

DESIGN

A cross-sectional study of monozygotic and dizygotic twins compared with a similar previously published normative control population.

METHODS

Forty-four healthy prepubertal twin children aged 4-11 years (20 monozygotic, 22 male) were studied. All subjects had 24-h ABPM and a fasting early morning plasma cortisol.

RESULTS

Twins had higher 24-h systolic blood pressure (BP) compared with controls with similar daytime and elevated night-time systolic BP (P > 0.3 and P < 0.01, respectively). Twins had reduced systolic and diastolic nocturnal BP dipping compared with controls (P < 0.0001 for both), and 61% of twins exhibited a < 10% fall in nocturnal BP. In the twin cohort there was no association between birth weight and daytime systolic BP (P = 0.6), nor any other ABPM parameter. There was no difference in BP parameters between dizygotic and monozygotic twins, and no difference between the lighter and heavier birthweight twins for any ABPM parameter. Fasting plasma cortisol was not associated with either birthweight (P = 0.2) or daytime systolic BP (P = 0.4).

CONCLUSIONS

Healthy prepubertal twins have increased nocturnal BP and reduced nocturnal BP dipping independent of zygosity or birthweight. These abnormalities may be a risk factor for the later development of hypertension in twins. As these BP abnormalities are not associated with twin birth weight, the twin model may not be appropriate in investigating the fetal origins of disease in later adult life.

Reduced insulin sensitivity during growth hormone therapy for short children born small for gestational age

OBJECTIVES

To examine the influence of recombinant human growth hormone (rhGH) therapy on insulin sensitivity in short children born small for gestational age (SGA).

STUDY DESIGN

Twelve short (height standard deviation score, -3.2 +/- 0.1) non-GH-deficient children SGA (7 boys/5 girls) were studied at 9.3 +/- 1.0 years of age. The insulin sensitivity index was measured with Bergman's minimal model before (11 children) and during (12 children) rhGH therapy (21 +/- 6 months) administered daily at 20 IU/m(2) per week. No child had a change in pubertal status during the study. In addition, 5 children who remained prepubertal had insulin sensitivity remeasured 3 months after rhGH therapy was suspended.

RESULTS

With rhGH therapy, insulin sensitivity fell 44% +/- 10% (P =.018), with a compensatory rise in the acute insulin response of 123% +/- 59% (P <.009). Reassessment of insulin sensitivity in 5 children (3 boys/2 girls) 3 months after suspension of rhGH occurred at 9.9 +/- 0.7 years. Insulin sensitivity remained unchanged after rhGH therapy was stopped: 31.6 (20.5-42.3) before treatment, 11.5 (5.7-24.4) with treatment, and 10.7 (6.2-16.9) 10(-4). min(-1) microU/mL after treatment.

CONCLUSIONS

Children SGA are known to have reduced insulin sensitivity. There was a further reduction in insulin sensitivity with rhGH therapy that did not recover 3 months after rhGH therapy was stopped.

IGFs and binding proteins in short children with intrauterine growth retardation

The aim of this study was to examine the relationship between the IGF-IGF binding protein (IGFBP) axis and insulin secretion in short intrauterine growth retardation (IUGR) children. Fifteen IUGR and 12 normal short prepubertal subjects had a 90-min frequently sampled iv glucose tolerance test performed to measure plasma glucose, insulin, IGF-I, IGF-II, IGFBP-3, and IGFBP-1. In addition, 29 nonobese prepubertal subjects of normal height had fasting plasma IGF-I and IGFBP-3 levels measured. In comparison to short normal subjects, IUGR subjects had higher plasma values for IGF-I (42 +/- 10 vs. 77 +/- 31 microg/liter; P < 0.0001), IGF-II (291 +/- 76 vs. 370 +/- 66 microg/liter; P < 0.008), IGFBP-3 (1.66 +/- 0.28 vs. 2.07 +/- 0.48 mg/liter; P < 0.0005), fasting insulin (2 +/- 1 vs. 4 +/- 2 mU/liter; P < 0.004), and acute insulin response (AIR; 215 +/- 36 vs. 504 +/- 90 mU/liter; P = 0.008). Nonobese subjects of normal height had higher plasma IGF-I (117 +/- 9 microg/liter; P < 0.0001) and IGFBP-3 (2.34 +/- 0.12 mg/liter) values than the IUGR group (P < 0.0005). During the frequently sampled iv glucose tolerance test, the magnitude of the AIR in short normal subjects was related to the fall in IGFBP-1 levels (P = 0.03); however, no relationship was seen between AIR and fall in IGFBP-1 in IUGR subjects (P = 0.24). In conclusion, short IUGR children have higher plasma IGF-I, IGF-II, and IGFBP-3, when compared with normal children matched for height, weight, and pubertal status. We speculate that hyperinsulinism secondary to insulin resistance may have led to these changes to the IGF-IGFBP axis in the IUGR group.

The changing presentation of children with newly diagnosed type 1 diabetes mellitus

Although it is known that the incidence of type 1 diabetes mellitus (DM) in childhood is progressively increasing, it is less clear whether the presentation of newly diagnosed DM is changing. The aim of this study was to establish whether any biochemical or clinical presentation parameters have altered over time. A retrospective study was performed comparing newly diagnosed children with DM in two 24 month time intervals, 8 yrs apart (1988-89 and 1995-96). Fifty-seven children were diagnosed with type 1 DM in 1988-89 and 70 children in 1995-96. At presentation, children born in the later cohort had a higher pH (p < 0.001) and lower serum glucose (p < 0.05). Although the frequency of diabetic ketoacidosis (DKA) was higher in the 1988/89 cohort (63% vs. 42% in 1995/96) the absolute number of children with DKA in each time interval was similar (33 subjects in 1988-89 vs. 30 subjects in 1995/96). Islet cell antibody (ICA) levels were very different between the two cohorts; higher antibody levels were found in the 1988/89 group (p < 0.01). DKA was also associated with higher ICA titres (p < 0.05). Hospital admission stay decreased from 6.5 DS to 3.4 DS over the 8-year period (p < 0.0001). At our institution, the presentation of children with type 1 DM is changing with many more children diagnosed before developing DKA. We speculate that a new environmental factor(s) may be responsible for the absolute increase in patients presenting without DKA, while older etiologies (both genetic and environmental) are responsible for the steady, unchanging number of patients with a more severe presentation. Greater awareness of diabetes in children is not the factor contributing to earlier diagnosis before DKA develops.

Obesity in Auckland school children: a comparison of the body mass index and percentage body fat as the diagnostic criterion

OBJECTIVES

First, to determine obesity rates in Auckland school children according to their ethnic group using two different criteria: the body mass index (BMI) and percentage body fat (PBF) derived from bioelectrical impedance analysis (BIA). Second to examine the relationship between BMI and body composition across ethnic groups to determine if BMI references from European children accurately reflect obesity in other ethnic groups.

DESIGN

A total of 2273 Auckland school children, aged 5-10.9 y had their height, weight and bioelectrical impedance measured. Using these measurements, each child's BMI, fat free mass, fat mass and PBF were derived.

RESULTS

In all 14.3% of children were obese using the recommended definition of obesity (BMI) greater than the 95th percentile). There was no clinically significant difference in the relationship between BMI and body composition in different ethnic groups. Obesity rates varied with ethnicity (P<0.0001) and were higher in Pacific Island (24.1%) and Maori (15.8%) than in European children (8.6%). Obesity rates also varied with age (P<0.03), with the highest rates in older children. PBF levels were higher in females than males (P<0.0001). Using a definition of obesity based on percentage body fat (PBF>30%), obesity rates were higher in all ethnic groups.

CONCLUSIONS

Obesity rates are high in Auckland school children and there are clear differences in obesity rates in different ethnic groups. If BMI criteria are used to define obesity in our population, we recommend the same standards be used for children of all ethnicities.

Foot-to-foot bioelectrical impedance analysis: a valuable tool for the measurement of body composition in children

OBJECTIVE

To determine the accuracy of foot-to-foot bioelectrical impedance analysis (BIA) and anthropometric indices as measures of body composition in children.

DESIGN

Comparison of foot-to-foot BIA and anthropometry to dual-energy X-ray absorptiometry (DEXA)-derived body composition in a multi-ethnic group of children.

SUBJECTS

: Eighty-two European, NZ Maori and Pacific Island children aged 4.9-10.9 y.

MEASUREMENTS

DEXA body composition, foot-to-foot bioelectrical impedance, height, weight, hip and waist measurements.

RESULTS

Using a BIA prediction equation derived from our study population we found a high correlation between DEXA and BIA in the estimation of fat-free mass (FFM), fat mass (FM) and percentage body fat (PBF) (r=0.98, 0.98 and 0.94, respectively). BIA-FFM underestimated DEXA-FFM by a mean of 0.75 kg, BIA-FM overestimated DEXA-FM by a mean of 1.02 kg and BIA-PBF overestimated DEXA-PBF by a mean of 2.53%. The correlation between six anthropometric indices (body mass index (BMI), ponderal index, Chinn's weight-for-height index, BMI standard deviation score, weight-for-length index and Cole's weight-for-height index) and DEXA were also examined. The correlation of these indices with PBF was remarkably similar (r=0.85-0.87), more variable with FM (r=0.77-0.94) and poor with FFM (r=0.41-0.75).

CONCLUSIONS

BIA correlated better than anthropometric indices in the estimation of FFM, FM and PBF. Foot-to-foot BIA is an accurate technique in the measurement of body composition.

Impaired insulin-mediated glucose uptake in monocytes of short children with intrauterine growth retardation

AIMS

To determine whether there was an impairment in insulin-mediated glucose uptake in monocytes from short children with intrauterine growth retardation (IUGR) when compared with control subjects.

METHODS

Circulating monocytes were isolated by histopaque gradient separation followed by adherence. Monocytes were incubated with insulin at the following concentrations; 0, 0.1, 0.2, 0.6, 1, 2 and 6 nm. 2-deoxyglucose (2-DG) uptake was measured after incubation with [(3)H]2-DG and expressed as pmol/min/10(6) cells. Insulin-stimulated glucose uptake was determined in two ways: 6 nm insulin concentration minus baseline (6-0 nm) and the regression slope of glucose uptake over the range of log insulin concentrations (slope value). Insulin sensitivity was determined from a 90-min frequently sampled intravenous glucose tolerance test with the minimal model.

RESULTS

Short children with IUGR (n = 16) had lower slope (4.6 +/- 1.1 vs. 9.5 +/- 2.0, p = 0.002) and 6-0 nm (8 +/- 2 vs. 15 +/- 3 pmol/min/10(6) cells, p = 0.048) glucose uptake values than normal children (n = 11). There was no difference in baseline glucose uptake between IUGR and normal children (36 +/- 5 vs. 48 +/- 7 pmol/min/10(6) cells). In the five subjects with IUGR that were evaluated, the in vivo insulin sensitivity index and glucose effectiveness were found to be positively correlated with insulin-mediated glucose uptake in monocytes (r = 0.54) and baseline glucose uptake in monocytes, respectively (r = 0.69).

CONCLUSIONS

Short children with IUGR have impairment in insulin-mediated glucose uptake in monocytes when compared with normal children. Our hitherto limited data indicate that insulin-mediated glucose uptake in monocytes is correlated with in vivo assessment of insulin sensitivity in children with IUGR.

Fetal origins of hyperphagia, obesity, and hypertension and postnatal amplification by hypercaloric nutrition

Environmental factors and diet are generally believed to be accelerators of obesity and hypertension, but they are not the underlying cause. Our animal model of obesity and hypertension is based on the observation that impaired fetal growth has long-term clinical consequences that are induced by fetal programming. Using fetal undernutrition throughout pregnancy, we investigated whether the effects of fetal programming on adult obesity and hypertension are mediated by changes in insulin and leptin action and whether increased appetite may be a behavioral trigger of adult disease. Virgin Wistar rats were time mated and randomly assigned to receive food either ad libitum (AD group) or at 30% of ad libitum intake, or undernutrition (UN group). Offspring from UN mothers were significantly smaller at birth than AD offspring. At weaning, offspring were assigned to one of two diets [a control diet or a hypercaloric (30% fat) diet]. Food intake in offspring from UN mothers was significantly elevated at an early postnatal age. It increased further with advancing age and was amplified by hypercaloric nutrition. UN offspring also showed elevated systolic blood pressure and markedly increased fasting plasma insulin and leptin concentrations. This study is the first to demonstrate that profound adult hyperphagia is a consequence of fetal programming and a key contributing factor in adult pathophysiology. We hypothesize that hyperinsulinism and hyperleptinemia play a key role in the etiology of hyperphagia, obesity, and hypertension as a consequence of altered fetal development.

Limitations of first-phase insulin response to evaluate insulin secretion in children

The first-phase insulin response (FPIR) is a widely used method to evaluate beta-cell function during the prediabetic phase of evolving type 1 diabetes mellitus (DM). The aim of the present study was to evaluate the influence of clinical and methodological variables on FPIR in normal children and adolescents. Children and adolescents who were first-degree relatives of those with type 1 DM and healthy young adults were studied. All subjects were islet cell antibody-negative. A FPIR test was performed on all subjects while fasting. Insulin samples were drawn at 0, 1, 2, 3, 4, 5, 6, 8, and 10 min after 0.3 g/kg of dextrose. FPIR(1-10) was calculated as the area under the FPIR curve corrected for baseline. Eighty-five subjects aged 4-22 yr were studied, 43 of whom were pre-pubertal, 24 pubertal, and 18 post-pubertal. FPIR(1-10) values were lower in the pre-pubertal group when compared to either the pubertal and post-pubertal groups (415 [179-965, 2SD], 756 [256-2 223] and 684 [235-1 180] mU/L, respectively; p<0.05). Obese subjects had a higher FPIR than non-obese subjects (856 vs. 520 mU/L; p<0.005). Despite correcting for the influence of puberty and obesity, there remained considerable unaccounted variability in FPIR(1-10) (R=0.46). Further variables found to influence FPIR(1-10) were: fasting insulin level (r(2)=0.49); weight for length index (r(2)=0.38); peak blood glucose level (r(2)=0.38, all p<0.001); and pre-pubertal age (r(2)=0.20, p<0.05).

CONCLUSION

FPIR exhibited wide inter-subject variability and was influenced by a number of clinical and methodological factors that make interpretation more difficult without more specifically defined standards.

Incidence of diabetes mellitus and impaired glucose tolerance in children and adolescents receiving growth-hormone treatment

BACKGROUND

Growth hormone (GH) contributes to insulin resistance, but whether children treated with GH are at increased risk of diabetes has not been established. We undertook a retrospective analysis of data from an international pharmacoepidemiological survey of children treated with GH to find out the incidence of impaired glucose tolerance and types 1 and 2 diabetes mellitus.

METHODS

Reports to the survey of abnormal glucose metabolism were investigated and classified. The incidence and age-distribution of type 1 diabetes were compared with values from a model of reference data. The incidence of type 2 diabetes was compared with data from two reports of children not treated with GH.

FINDINGS

85 (0.36%) of 23333 children were reported with abnormal glucose metabolism. After investigation, 43 had confirmed glucose disorders (11 with type 1 diabetes, 18 with type 2 diabetes, and 14 with impaired glucose tolerance). The incidence and age at diagnosis of type 1 diabetes in children treated with GH did not differ from expected values. The incidence of type 2 diabetes was 34.4 cases per 100000 years of GH treatment which was six-fold higher than reported in children not treated with GH. Type 2 diabetes did not resolve after GH therapy was stopped.

INTERPRETATION

GH treatment did not affect the incidence of type 1 diabetes mellitus in any age group. We postulate that the higher than expected incidence of type 2 diabetes mellitus with GH treatment may be an acceleration of the disorder in predisposed individuals.

Insulin resistance in short children with intrauterine growth retardation

Epidemiological studies have demonstrated an association between intrauterine growth retardation and an increased risk of adult diseases that include essential hypertension, noninsulin-dependent diabetes mellitus, and ischemic heart disease. A common feature of these diseases is insulin resistance. To investigate whether abnormal insulin sensitivity was a characteristic of subjects with intrauterine growth retardation (IUGR), we compared two groups of short prepubertal children: a group with IUGR (birth weight less than the tenth percentile; n = 15) and a normal birth weight group (n = 12). Subjects underwent a modified frequently sampled iv glucose tolerance test that permitted calculation of the acute insulin response, insulin sensitivity index, and glucose effectiveness. A marked difference in the insulin sensitivity index was noted between groups, with the IUGR group being less insulin sensitive [6.9 vs. 16.9 10(-4)min-1.(microU/mL); P = 0.0048]. The acute insulin response was also significantly different between groups, with IUGR subjects having higher insulin levels (445 vs. 174 microU/mL; P = 0.005). There was no difference in glucose effectiveness between groups. Short prepubertal IUGR children have a specific impairment in insulin sensitivity compared to their normal birth weight peers. In short IUGR children, impaired insulin sensitivity is a potential marker for the early identification and intervention in the development of late adult-onset noninsulin-dependent diabetes mellitus.

Factors predictive of response to growth hormone therapy in Turner's syndrome

In Turner's syndrome there is marked heterogeneity of growth response to growth hormone (GH) therapy. The study aim was to identify pretreatment factors that influence response to GH therapy. The 70 subjects recruited were prepubertal, had not received sex steroids and had received 28 units/m2/week of GH for > or = 1 year. Pretreatment variables associated with the greatest improvement in height SDS (r2 = 0.58) were weight for length index (p = 0.0001), target height (p = 0.004), bone age delay (p = 0.008) and age (p = 0.04). In conclusion, during two years of GH therapy the best growth response occurred in girls who were younger, heavier, had a delayed bone age and tall parents. Height SDS as a continuous variable is the most effective measure of growth when considering pretreatment factors that may influence response to GH therapy.

High and low dose initial thyroxine therapy for congenital hypothyroidism

OBJECTIVE

To assess factors influencing thyroxine (T4) levels 1 month after initiating replacement therapy for congenital primary hypothyroidism.

METHODOLOGY

A retrospective review of 41 children with congenital hypothyroidism who received either high or low dose initial T4 therapy. Thyroid scintiscan was performed, and T4 levels determined before starting treatment and after 1 month.

RESULTS

T4 levels at 1 month were correlated (r2 = 0.38, P < 0.001) with the pretreatment T4 level (r = 0.48), as well as with the T4 dose (r = 0.46). Suboptimal treated T4 levels (< 130 nmol/L) were seen with greater frequency in infants with thyroid agenesis (7/11) rather than ectopia (7/28, P < 0.03), despite receiving similar doses of thyroxine. Infants with suboptimal treated T4 levels had lower pretreatment T4 levels than those with optimal levels (21 +/- 7 vs 48 +/- 34 nmol/L, P < 0.02). Biochemical hyperthyroidism (T4 > 216 nmol/L) occurred in six patients; four of six had ectopia.

CONCLUSIONS

These data suggest that infants with little residual thyroid function should receive higher initial T4 doses than those with significant ectopia.

Newborn screening for congenital adrenal hyperplasia in New Zealand

OBJECTIVE

To evaluate the efficacy and efficiency of newborn screening for classic congenital adrenal hyperplasia (CAH) in New Zealand.

DESIGN

All infants younger than 6 weeks of age identified by newborn screening between December 1984 and December 1993 were included.

RESULTS

23 cases of classic CAH (20 salt-losers) were identified. The incidence of classic CAH was 1 in 23,344. Screening identified 3 of 9 virilized female infants whose disease had not been detected clinically. Screening alone identified all 11 male infants. Notification of cases occurred at 11 +/- 3 days of age. There was a delay in treatment of the group identified by screening alone (n = 14) until 13 days of age (range, 4 to 35 days); at that time 11 infants had hyponatremia and 10 had hyperkalemia. Symptoms of vomiting, poor feeding, and shock were common after 10 days of age (2/10, < 10 days, and 8/8, 11 to 16 days of age).

CONCLUSIONS

Newborn CAH screening is the only method of identifying male infants with classic CAH without a family history of CAH before symptoms develop, as well as a significant portion of overlooked virilized female infants. So that clinical or significant biochemical deterioration can be avoided, pediatrician notification of screening results and treatment should be started before 10 days of age.

Congenital idiopathic growth hormone deficiency associated with prenatal and early postnatal growth failure. The International Board of the Kabi Pharmacia International Growth Study

To assess the role of growth hormone in fetal and infant growth, we analyzed the pretreatment data on 52 patients with a diagnosis of congenital growth hormone deficiency before 2 years of age, obtained from the Kabi Pharmacia International Growth Study. These infants had reduced birth-length standard deviation scores, an excess of birth weight relative to length, and progressive growth failure. We conclude that congenital growth hormone deficiency may cause impaired growth in utero and early infancy, and that growth hormone plays an important role in perinatal and infantile growth.

Diminished growth hormone-binding protein in children with insulin-dependent diabetes mellitus

Two distinct GH-binding proteins (GHBP) are present in circulation in the human. The major GHBP (high affinity GHBP) is homologous to the extracellular portion of the GH receptor and the concentration of this protein in circulation may reflect the status of the GH receptor in the tissues. To gain information about the concentration of GHBPs in children with insulin-dependent diabetes mellitus (IDDM), we measured GHBP in the serum of 46 children with IDDM and compared it to that in 53 healthy control subjects matched for age and sexual maturity. The total GHBP concentration in the group of pubertal and postpubertal IDDM patients was lower than that measured in the control group (mean +/- SEM: 7.8 +/- 0.4 vs. 9.0 +/- 0.5%, P = 0.05). The diabetic children in stages II to IV of puberty had a lower GHBP level compared to their healthy controls (7.6 +/- 0.4 vs. 9.1 +/- 0.5%, P = 0.02), whereas the difference between the diabetic and control group of postpubertal children was not statistically different (8.3 +/- 0.7 vs. 9.7 +/- 0.7%, P = 0.1). In a randomly selected subset of eight patients and eight controls, the concentration of the individual GHBPs (i.e. high affinity and low affinity (GHBP) was estimated by gel chromatography. There was no difference in the low affinity GHBP between the two groups (9.9 +/- 0.6% vs. 9.9 +/- 0.4%), but the high affinity GHBP was less in the diabetic group than in the control group (10.5 +/- 0.9 vs. 15.6 +/- 1.0%, P less than 0.01). In the diabetic group, there was no correlation between the GHBP levels and age, duration of diabetes, hemoglobin A1, or insulin dose. We conclude that in IDDM there is less of the high affinity GHBP, suggesting a decrease in the number of GH receptors in these patients. This decrease may contribute to GH resistance manifesting as decreased insulin-like growth factor-I levels despite high GH levels in patients with IDDM.

Evaluation of a pen injector system for growth hormone treatment

The increasing use of human growth hormone (hGH) treatment has resulted in the introduction of a number of alternative delivery systems to conventional syringe and needle administration. We examined patients' evaluation of a new delivery system, the Kabipen (Kabi-Vitrum). We also assessed the accuracy of hGH delivery by the Kabipen. Of the 77 survey respondents 13 had used only the Kabipen, 14 the syringe only, and 50 had used both systems. Altogether 46 (92%) of those who had used both systems preferred the Kabipen. Children over 10 years were more likely to self administer hGH with the Kabipen (64%) than syringe (25%). Patient instructions, convenience of use, and comfort of use were rated better for the Kabipen than syringe. With a dose setting of 2 units the Kabipen delivered a mean (SD) of 1.997 (0.073) units with 102.5% recovery from a unit cartridge. In summary the Kabipen is an accurate device clearly preferred by the majority of hGH recipients surveyed.

Transplacental passage of insulin in pregnant women with insulin-dependent diabetes mellitus. Its role in fetal macrosomia

BACKGROUND AND METHODS

Fetal macrosomia occurs despite nearly normal maternal blood glucose levels in women with diabetes treated with insulin. We examined the hypothesis that it may be caused by insulin transferred as an insulin-antibody complex from the mother to her fetus. We adapted and validated a method based on high-performance liquid chromatography and used it to quantitate insulin in small volumes (0.5 to 1.0 ml) of cord serum from 51 infants born to mothers with insulin-dependent diabetes mellitus.

RESULTS

In mothers receiving only human insulin (n = 6), only human insulin was detected in cord serum. Of the remaining 45 infants, whose mothers received animal insulin during pregnancy, 28 (group 1) had levels of animal (bovine or porcine) insulin (mean [+/- SE], 707 +/- 163 pmol per liter) that constituted 27.4 +/- 2.5 percent of the total insulin concentration (2393 +/- 500 pmol per liter) measured in the cord serum. The cord-serum insulin concentration in the remaining 17 infants (group 2), in whom only human insulin was detected (381 +/- 56 pmol per liter), was only 15 percent of that in group 1 (P less than 0.001). There was a significant correlation between the maternal and the cord-serum concentrations of anti-insulin antibody and the concentration of animal insulin in the baby (r = 0.77, P less than 0.01, and r = 0.76, P less than 0.001, respectively), suggesting that the animal insulin was transferred as an insulin-antibody complex. In group 1 the mean concentration of animal insulin in cord serum was higher in the 12 infants with macrosomia than in the 16 infants without the condition (1113 +/- 321 vs. 402 +/- 110 pmol per liter; P less than 0.05), and the concentration of animal insulin in cord serum correlated with birth weight (r = 0.39, P less than 0.05). The maternal glycosylated hemoglobin values and the incidence of respiratory distress syndrome were similar in groups 1 and 2.

CONCLUSIONS

Considerable amounts of antibody-bound insulin are transferred from mother to fetus during pregnancy in some women with insulin-dependent diabetes mellitus; the extent of transfer correlates with the maternal concentration of anti-insulin antibody. The correlation between macrosomia and the concentrations of animal insulin in cord serum indicates that the transferred insulin has biologic activity and suggests that the formation of antibody to insulin in the mother is a determinant of fetal outcome independent of maternal blood glucose levels.

The modified minimal model: application to measurement of insulin sensitivity in children

The modified minimal model (MMM), a recently introduced method that assesses insulin sensitivity (SI) by a computed mathematical analysis of the relation between the change in insulin and glucose clearance after a bolus of iv glucose, followed 20 min later by a bolus of tolbutamide, has been standardized in adults, but this method has not been validated in children. We performed an abbreviated 90-min MMM test in 50 children who were siblings of patients with insulin-dependent diabetes mellitus and 7 healthy adult volunteers and compared the results to the standard 180-min MMM test in 11 of these subjects. The cohort consisted of 29 prepubertal children [16 males and 13 females; 8.7 +/- 2.0 (mean +/- SEM) yr old]; 16 pubertal children defined as less than 17 yr of age and Tanner stage 2-5 (8 males and 8 females; 13.4 +/- 1.8 yr old), and 12 postpubertal subjects (7 males and 5 females; 18.2 +/- 0.9 yr old), with no significant difference in the weight for length index (WLI) among the 3 groups and with sera of all subjects negative for islet cell antibodies and insulin autoantibodies. The test procedure consisted of 3 baseline blood samples over 30 min, followed at zero time by 0.3 g/kg 25% dextrose infused iv over 1 min and an iv injection of tolbutamide (5 mg/kg) 20 min later; sequential blood samples for glucose and insulin measurements were withdrawn from zero time until completion 90 or 180 min later. In the 11 subjects who underwent both the standard and the abbreviated tests, there was no significant difference between the SI estimated by the 2 methods provided that glucose and insulin values were interpolated at 180 min during the computer calculations of the abbreviated test. Using the 90-min abbreviated test, the SI of the pubertal subjects (2.92 +/- 0.45) was markedly less than that of the prepubertal subjects (6.57 +/- 0.45; P = 0.0001). While the postpubertal group value of 4.63 +/- 0.86 was significantly higher than that of the pubertal group (P = 0.0001), the pre- and postpubertal groups remained significantly different (P = 0.0001). The 10 obese subjects with WLI greater than 120% had a lower SI (3.5 +/- 0.53) than the 47 nonobese subjects with WLI less than 120% (SI = 5.48 +/- 0.42; P less than 0.04), and there was a negative correlation between SI and WLI. None of the study subjects experienced symptomatic hypoglycemia during the test.(ABSTRACT TRUNCATED AT 400 WORDS)