Carbohydrate and lipid metabolism during various growth hormone dosing regimens in girls with Turner syndrome. Dutch Working Group on Growth Hormone

Hyperglycemia in Turner syndrome: Impact, mechanisms, and areas for future research

Turner syndrome (TS) is a common chromosomal disorder resulting from complete or partial absence of the second sex chromosome. Hyperglycemia, ranging from impaired glucose tolerance (IGT) to diabetes mellitus (DM), is common in TS. DM in individuals with TS is associated with an 11-fold excess in mortality. The reasons for the high prevalence of hyperglycemia in TS are not well understood even though this aspect of TS was initially reported almost 60 years ago. Karyotype, as a proxy for X chromosome (Xchr) gene dosage, has been associated with DM risk in TS - however, no specific Xchr genes or loci have been implicated in the TS hyperglycemia phenotype. The molecular genetic study of TS-related phenotypes is hampered by inability to design analyses based on familial segregation, as TS is a non-heritable genetic disorder. Mechanistic studies are confounded by a lack of adequate TS animal models, small and heterogenous study populations, and the use of medications that alter carbohydrate metabolism in the management of TS. This review summarizes and assesses existing data related to the physiological and genetic mechanisms hypothesized to underlie hyperglycemia in TS, concluding that insulin deficiency is an early defect intrinsic to TS that results in hyperglycemia. Diagnostic criteria and therapeutic options for treatment of hyperglycemia in TS are presented, while emphasizing the pitfalls and complexities of studying glucose metabolism and diagnosing hyperglycemia in the TS population.

Cardiovascular phenotype in Turner syndrome--integrating cardiology, genetics, and endocrinology

Cardiovascular disease is emerging as a cardinal trait of Turner syndrome, being responsible for half of the 3-fold excess mortality. Turner syndrome has been proposed as an independent risk marker for cardiovascular disease that manifests as congenital heart disease, aortic dilation and dissection, valvular heart disease, hypertension, thromboembolism, myocardial infarction, and stroke. Risk stratification is unfortunately not straightforward because risk markers derived from the general population inadequately identify the subset of females with Turner syndrome who will suffer events. A high prevalence of endocrine disorders adds to the complexity, exacerbating cardiovascular prognosis. Mounting knowledge about the prevalence and interplay of cardiovascular and endocrine disease in Turner syndrome is paralleled by improved understanding of the genetics of the X-chromosome in both normal health and disease. At present in Turner syndrome, this is most advanced for the SHOX gene, which partly explains the growth deficit. This review provides an up-to-date condensation of current state-of-the-art knowledge in Turner syndrome, the main focus being cardiovascular morbidity and mortality. The aim is to provide insight into pathogenesis of Turner syndrome with perspectives to advances in the understanding of genetics of the X-chromosome. The review also incorporates important endocrine features, in order to comprehensively explain the cardiovascular phenotype and to highlight how raised attention to endocrinology and genetics is important in the identification and modification of cardiovascular risk.

The benefits of growth hormone therapy in patients with Turner syndrome, Noonan syndrome and children born small for gestational age

This review will summarize the effects of growth hormone (GH) on height, body composition, bone and psychosocial parameters in children with Turner syndrome or Noonan syndrome and those born small for gestational age. The safety of GH treatment in children with these diagnoses is also reported. Despite the reported efficacy and safety of GH in these indications, however, not all children achieve their target height potential, due in some part to poor adherence to GH therapy regimens; indeed up to 50% of children are less than fully compliant with treatment. With this in mind the present and future administration of GH therapy is discussed with respect to advances being made in the presentation of GH for injection and advances in GH injection devices. It is hoped that such progress, aimed at making the administration of GH easier and less painful for the patient will improve treatment adherence and outcome benefits.

Recombinant human growth hormone in the treatment of Turner syndrome

Turner syndrome (TS) is a common chromosomal disorder in women that is associated with the absence of one of the X chromosomes. Severe short stature and a lack of pubertal development characterize TS girls, causing psychosocial problems and reduced bone mass. The growth impairment in TS seems to be due to multiple factors including an abnormal growth hormone (GH) - insulin-like growth factor (IGF) - IGF binding protein axis and haploinsufficiency of the short stature homeobox-containing gene. Growth hormone and sex steroid replacement therapy has enhanced growth, pubertal development, bone mass, and the quality of life of TS girls. Recombinant human GH (hGH) has improved the height potential of TS girls with varied results though, depending upon the dose of hGH and the age of induction of puberty. The best final adult height and peak bone mass achievement results seem to be achieved when hGH therapy is started early and puberty is induced at the normal age of puberty in a regimen mimicking physiologic puberty. The initiation of estradiol therapy at an age-appropriate time may also help the TS patients avoid osteoporosis during adulthood. Recombinant hGH therapy in TS seems to be safe. Studies so far show no adverse effects on cardiac function, glucose metabolism or any association with neoplasms but research is still in progress to provide conclusive data on long-term safety.

Effects of Growth Hormone on Growth, Insulin Resistance and Related Hormones (Ghrelin, Leptin and Adiponectin) in Turner Syndrome

BACKGROUND

Concomitant evaluation of the metabolic and growth-promoting effects of growth hormone (GH) therapy in Turner syndrome (TS) may be used in the prediction of the growth response to GH therapy.

AIM

To evaluate the metabolic effects of GH therapy in TS and correlation with the short-term growth response.

PATIENTS

24 prepubertal children with TS, aged 9.4 +/- 2.6 years were followed for auxology and IGF-I, IGFBP-3, leptin, ghrelin, adiponectin, lipids and OGTT results in a prospective multicenter study.

INTERVENTION

GH (Genotropin) in a dose of 50 microg/kg/day for 1 year.

RESULTS

Height standard deviation score (SDS) increased from -3.9 +/- 1.5 to -3.5 +/- 1.4 (p = 0.000) on therapy. BMI did not change. IGF-I SDS increased from -2.3 +/- 0.4 to -1.6 +/- 1.1 at 3 and 6 months (p = 0.001) and decreased thereafter. Serum leptin decreased significantly from 2.3 +/- 3.9 to 1.7 +/- 5.3 ng/ml (p = 0.022) at 3 months and increased afterwards. Serum ghrelin decreased from 1.2 +/- 0.8 to 0.9 +/- 0.4 ng/ml (p = 0.005) with no change in adiponectin. Basal and stimulated insulin levels also increased significantly. Delta height SDS over 1 year showed a significant correlation with Delta IGF-I(0-3 months) (r = 0.450, p = 0.027).

CONCLUSION

IGF-I may be considered as a marker of growth response in TS at short term. Leptin shows a decrease at short term but does not have a correlation with growth response. The decrease in ghrelin in face of unchanged weight seems to be associated with increase in IGF-I and insulin levels. The unchanged adiponectin levels in spite of an increase in insulin levels indicates that adiponectin is mainly affected by weight, not insulin.

[Evaluation of insulin resistance and lipid profile in turner syndrome]

OBJECTIVE

To evaluate the presence of insulin resistance (IR) and changes in lipid profile in Turner Syndrome (TS), and to check the influence of age, karyotype, systemic arterial hypertension (SAH), height, weight, body mass index (BMI), and pubertal development.

PATIENTS AND METHODS

A transversal study of 35 TS patients, confirmed with karyotype (5 to 43 years), without previous use of anabolic steroid or hGH, with evaluation of blood pressure, pubertal development, anthropometric data, measurement of waist (W), hip (H), W to H ratio, total cholesterol, HDL, triglycerides (TGC), LDL, insulin and glucose. HOMA and QUICKI indexes were calculated, as well as glucose to insulin ratio (G/I). Data were examined by the Mann-Whitney and Spearman tests.

RESULTS

Ten patients were >20 years. Seventeen had a 45,X karyotype and 6 structural aberrations; differences of the variables in relation to the karyotypes were not observed; 15 were nonpubertal and 20 pubertal; TGC and HOMA were significantly higher in puberty, while G/I was lower. Seven had normal height, 8 had BMI >25 Kg/m2 (6 between 25 and 30, and 2 >30), and 19 W/H >0.85. Cholesterol levels were 180 +/- 42mg% (4 >240); HDL 57 +/- 16mg%; LDL 99 +/- 34 mg%; TGC 108 +/- 96 mg% (2 >200); HOMA 1.01 +/- 0.71; QUICKI 0.4 +/- 0.04 and G/I 23.5 +/- 12.1 (2 <7.0).

CONCLUSIONS

Changes were observed in lipid profile independent of age, karyotype, SAH and obesity, but associated with IR. The frequency of IR was lower than described in literature, and seems to be directly linked to chronological age, obesity and estrogen therapy.

Coordinating care for children with Turner syndrome

Turner syndrome is a systemic disease requiring a multi-system management approach. This includes attention to the endocrine system, cardiovascular system, renal system, gastrointestinal system, ears, eyes, skeletal system, and skin, as well as to the psychology of the patient and the family. The primary care physician is central to the care of these patients. In addition to anticipating, diagnosing, and treating the various problems that may arise in patients with Turner syndrome, the primary care physician must coordinate the fairly large healthcare team needed for optimal care.

Effect of discontinuation of long-term growth hormone treatment on carbohydrate metabolism and risk factors for cardiovascular disease in girls with Turner syndrome

GH treatment increases insulin levels in girls with Turner syndrome (TS), who are already predisposed to develop diabetes mellitus and other risk factors for developing cardiovascular disease. Therefore, in the present study, we investigated carbohydrate metabolism and several other risk factors that may predict development of cardiovascular disease in girls with TS after discontinuation of long-term GH treatment. Fifty-six girls, participating in a randomized dose-response study, were examined before, during, and 6 months after discontinuing long-term GH treatment with doses of 4 IU/m(2).d ( approximately 0.045 mg/kg.d), 6 IU/m(2).d, or 8 IU/m(2).d. After a minimum of 4 yr of GH treatment, low-dose micronized 17beta-estradiol was given orally. Mean (SD) age at 6 months after discontinuation of GH treatment was 15.8 (0.9) yr. Mean duration of GH treatment was 8.8 (1.7) yr. Six months after discontinuation of GH treatment, fasting glucose levels decreased and returned to pretreatment levels. The area under the curve for glucose decreased to levels even lower than pretreatment level (P < 0.001). Fasting insulin levels and the area under the curve for insulin decreased to levels just above pretreatment level (P < 0.001 for both), although being not significantly different from the control group. No dose-dependent differences among GH dosage groups were found. At 6 months after discontinuation, impaired glucose tolerance was present in 1 of 53 girls (2%), and none of the girls developed diabetes mellitus type 1 or 2. Compared with pretreatment, the body mass index SD-score had increased (P < 0.001), and the systolic and diastolic blood pressure SD-score had decreased significantly at 6 months after discontinuation of GH treatment (P < 0.001 for both) although remaining above zero (P < 0.001, P < 0.05, and P < 0.005, respectively). Compared with pretreatment, total cholesterol (TC) did not change after discontinuation of GH treatment, whereas the atherogenic index [AI = TC/high-density lipoprotein cholesterol (TC/HDL-c)] and low-density lipoprotein cholesterol (LDL-c) had decreased; and both HDL-c and triglyceride levels increased (P < 0.001 for AI, LDL-c, and HDL-c; P < 0.05 for triglyceride). Compared with the control group, AI, serum TC, and LDL-c levels were significantly lower (P < 0.001 for all), whereas HDL-c levels were significantly higher (P < 0.05). In conclusion, after discontinuation of long-term GH treatment in girls with TS, the GH-induced insulin resistance disappeared, blood pressure decreased but remained higher than in the normal population, and lipid levels and the AI changed to more cardio-protective values.

The impact and management of Turner's syndrome in adult life

Turner's syndrome (TS), caused by an absent or structurally abnormal X chromosome, affects 1 in 2500 live female births. Most medical attention has focused on the attainment of final height in childhood and, when this has been achieved, many women are discharged to primary care. It has become increasingly evident that adults with Turner's syndrome are susceptible to a range of disorders such as osteoporosis, hypothyroidism and diabetes. Because of these, and because of the need for long-term oestrogen replacement, it seems most practical for adult health surveillance in TS to come under the remit of the endocrinologist. It must be accepted, however, that the reduced life expectancy in women with TS is largely accounted for by cardiovascular disease. Also, the commonly observed social isolation in adults with TS can be linked to deafness that is increasingly prevalent in an ageing group. Co-ordination of all these issues requires a dedicated multidisciplinary clinic along the lines of those in place in diabetes.

Turner's syndrome in adulthood

Turner's syndrome is the most common chromosomal abnormality in females, affecting 1:2,500 live female births. It is a result of absence of an X chromosome or the presence of a structurally abnormal X chromosome. Its most consistent clinical features are short stature and ovarian failure. However, it is becoming increasingly evident that adults with Turner's syndrome are also susceptible to a range of disorders, including osteoporosis, hypothyroidism, and renal and gastrointestinal disease. Women with Turner's syndrome have a reduced life expectancy, and recent evidence suggests that this is due to an increased risk of aortic dissection and ischemic heart disease. Up until recently, women with Turner's syndrome did not have access to focused health care, and thus quality of life was reduced in a significant number of women. All adults with Turner's syndrome should therefore be followed up by a multidisciplinary team to improve life expectancy and reduce morbidity.

Perinatal 'programming' of insulin resistance in childhood: critical impact of neonatal insulin and low birth weight in a risk population

AIM

Low birth weight may predispose to later insulin resistance and hyperinsulinaemia, but the pathophysiological mechanisms are unclear. The perinatal endocrine situation may play an important role, but has been little studied. Children of mothers with diabetes during pregnancy are an important risk population for later insulin resistance and hyperinsulinaemia. We therefore examined relationships between birth weight, insulin and insulin resistance at birth, and insulin secretion and insulin resistance in infancy in these children.

METHODS

We studied 104 infants of mothers with Type 1 diabetes mellitus during pregnancy. Oral glucose tolerance tests (area under the curve of glucose, AUCG) with determination of insulin (area under the curve of insulin, AUCI) were performed at 1-5 years of age. Using correlation and regression analysis, birth data were related to insulin secretion (AUCI) and stimulated insulin/glucose ratio (AUCI/AUCG) in childhood.

RESULTS

Children with an AUCI in the highest tertile of distribution had the lowest birth weights. Birth weight was negatively correlated to AUCI in childhood (P = 0.03). Insulin/glucose ratio at birth was raised in infants with an AUCI in the upper tertile, accompanied by a positive correlation between insulin/glucose ratio at birth and AUCI (P = 0.02). Insulin and insulin/glucose ratio at birth were both positively correlated to AUCI/AUCG (P = 0.04 and P = 0.02 respectively), while the correlation between birth weight and AUCI/AUCG was not significant (P = 0.12). In a stepwise regression analysis, insulin/glucose ratio contributed as much as birth weight to AUCI in childhood. Birth weight, however, was significantly negatively related to AUCI/AUCG only when the insulin/glucose ratio at birth was included in the regression model.

CONCLUSIONS

Insulin and insulin resistance at birth show a positive relation to insulin secretion and insulin resistance in later life, in addition to the influence of a low birth weight, but independent of it. Perinatal and neonatal insulin, known to be of critical importance for long-term outcome, should be evaluated in future studies on the 'small baby syndrome'.

Carbohydrate metabolism during long-term growth hormone treatment in children with short stature born small for gestational age

OBJECTIVE

To assess possible side-effects of long-term continuous growth hormone (GH) treatment on carbohydrate (CH) metabolism in children with short stature born small for gestational age.

DESIGN

In a prospective, randomised double-blind, dose-response multicentre trial, the effect of GH treatment on CH metabolism was evaluated, comparing two GH dosages [3 vs. 6 IU/(m(2) body surface.day)].

PATIENTS

Seventy-eight children with short stature (height SD-score < - 1.88) born small for gestational age (birth length SD-score < - 1.88) being all prepubertal with a mean (SD) chronological age of 7.3 (2.2) years before start of treatment.

MEASUREMENTS

Glucose and insulin concentrations during oral glucose tolerance tests (OGTTs) and glycosylated haemoglobin (HbA(1c)) were measured before and during 6 years of GH treatment.

RESULTS

Before treatment, the glucose response to oral glucose after 120 min was in six of the 78 children (8%) above 7.8 mmol/l but below 11.1 mmol/l, indicating impaired glucose tolerance (IGT), whereas after 6 years of GH treatment, IGT was found in 4% of the children. None of the children developed diabetes mellitus. Mean fasting glucose levels had increased significantly by 0.5 mmol/l after 1 year of GH treatment, without a further increase thereafter. The 2-h area under the curve adjusted for fasting levels (AUCab) for glucose and the HbA(1c) levels were lower after 6 years of GH treatment compared to baseline. During GH treatment, all HbA(1c) levels were in the normal range. In contrast to the effects on glucose levels, GH treatment induced considerably higher fasting insulin levels and glucose-stimulated insulin levels. The increase in AUCab for insulin occurred particularly during the first year of treatment, whereas the fasting insulin levels showed a further increase from one to six years. As a result, the 30- and 120-min ratios of insulin to glucose were higher during GH treatment compared to the start of treatment. The children who remained prepubertal during the entire study period showed similar patterns in glucose and insulin levels compared to the children who entered puberty. None of the observed changes were different between the GH dosage groups.

CONCLUSIONS

Continuous GH treatment during 6 years in children with short stature born small for gestational age has no adverse effects on glucose levels, even with dosages up to 6 IU/(m(2) d). However, as has been reported in other patient groups, GH treatment induces higher fasting insulin levels and glucose-stimulated insulin levels, indicating relative insulin resistance. Since the consequences of long-term hyperinsulinism during childhood are unknown, careful follow-up of these GH-treated children born small for gestational age is required.

Carbohydrate metabolism during growth hormone treatment and after discontinuation of growth hormone treatment in girls with Turner syndrome treated with once or twice daily growth hormone injections

OBJECTIVE

To assess possible side-effects of treatment with supraphysiological GH dosages on carbohydrate (CH) metabolism in girls with Turner syndrome (TS) during GH treatment until adult height is reached as well as after discontinuation of GH treatment.

DESIGN

In a prospective, randomized injection frequency-response study, the effect of GH treatment in combination with low dose ethinyl oestradiol on CH metabolism was evaluated, comparing twice daily (BID) with once daily (OD) injections of a total GH dose of 6 U/m2/day until adult height was reached.

PATIENTS

Nineteen untreated girls with TS, mean (SD) pretreatment age 13.3 (1.7) (range 11.0-17.6) year.

MEASUREMENTS

Glucose and insulin concentrations during oral glucose tolerance tests (OGTT) were measured before and during GH treatment, as well as at 6 months after discontinuation of GH treatment.

RESULTS

GH treatment was discontinued after a mean of 43 (range 27-57) months. In one of the 19 girls, a different girl at each time point before, during and after discontinuation of GH treatment, the glucose response to OGTT after 120 minutes was above 7.8 mmol/l but below 11.1 mmol/l, indicating impaired glucose tolerance. None of the girls developed diabetes mellitus. Fasting glucose levels did not significantly change during, or after discontinuation of GH treatment. The 3 h area under the curve for time-concentration adjusted for fasting levels during the OGTT for glucose showed a significant decrease during GH treatment. In contrast to the glucose levels, GH treatment induced considerably higher insulin levels compared to pretreatment values. After discontinuation of GH insulin levels decreased to values comparable with pretreatment levels. None of these observed changes were different between the GH injection frequency groups. The changes in CH variables during and after discontinuation of GH were not related to changes in body mass index.

CONCLUSIONS

GH treatment with 6 U/m2/day in combination with low dose ethinyl oestradiol in girls with Turner syndrome aged > or =11 years did not negatively influence glucose levels, but induced higher levels of insulin indicating relative insulin resistance. These changes in insulin levels were independent of the frequency of the GH injections (once vs. twice daily). After discontinuation of GH treatment, insulin values decreased to baseline levels.