Reduced secretion of gastric inhibitory polypeptide in Turner patients with impaired glucose tolerance

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.

Short-term growth hormone treatment in girls with Turner syndrome decreases fat mass and insulin sensitivity: a randomized, double-blind, placebo-controlled, crossover study

BACKGROUND

Most girls with Turner syndrome (TS) receive growth hormone (GH) treatment during childhood and adolescence, but controlled data on the effects on body composition and glucose metabolism are lacking.

OBJECTIVE

To study the effects of GH treatment on insulin sensitivity, glucose metabolism, bone turnover, and body composition.

METHODS

A randomized, placebo-controlled, crossover study was conducted with girls with TS. All girls with TS were treated with GH 0.1 IU/kg/d subcutaneously at bedtime or with placebo for 2 months and studied at the end of each period. Control subjects were studied once without treatment. Twelve girls with TS, aged 9.5 to 14.8 years (median: 12.9 years) and 16 age-matched control subjects (10.3-16.0 years; median: 12.1 years) were studied. Twenty-four-hour sampling of blood was performed; GH, insulin-like growth factor I (IGF-I), IGF binding proteins (IGFBPs), insulin, glucose, and lipolytic and gluconeogenic precursors were assayed, followed by an oral glucose tolerance test. Body composition was evaluated by dual-energy x-ray absorptiometry scanning and body mass index (BMI). Fasting bone markers were measured.

RESULTS

Height was reduced in TS as compared with control subjects. In the placebo situation, 24-hour integrated GH as well as IGF-I was significantly reduced in girls with TS compared with control subjects. Controlling for differences in lean body mass (LBM; or fat mass [FM]) and sexual development did not explain the difference in 24-hour integrated GH. Differences in sexual development, BMI, FM, insulin sensitivity, and IGFBP-3 could explain the difference in IGF-I between TS and control subjects. Carbohydrate metabolism in TS was comparable with control subjects. GH treatment induced insulin resistance, with increments in fasting glucose and insulin, as well as 24-hour insulin. Circulating levels of lipid and gluconeogenic substrates were comparable in TS and control subjects and unchanged in response to treatment. Bone markers increased in response to GH. Total FM was increased in girls with TS, accounted for by an increased FM in the arms and trunk, whereas LBM was decreased. Especially LBM in the legs was decreased. Overall, bone mineral content was diminished. Treatment with GH reduced FM in TS, especially in the arms and legs, and likewise increased total LBM, primarily in the trunk.

CONCLUSION

This study documented evidence of impaired GH secretion and action, disproportionate body composition, but a normal carbohydrate metabolism in girls with TS. Short-term GH administration was associated with favorable changes in body composition but also with relative impairment of glucose tolerance and insulin sensitivity. We recommend that glucose metabolism be monitored carefully during long-term GH treatment in these patients.

Turner syndrome: final height, glucose tolerance, bone density and psychosocial status in 25 adult patients

The information available on the medical and psychosocial status of patients with Turner syndrome beyond the paediatric age group is scarce. We therefore studied 25 unselected women with cytogenetically proven Turner syndrome (age 20-50 years), who never received any growth-promoting therapy, and ten control women (25-48 years). In addition to anthropometric measurements, an oral glucose tolerance test was performed, auto-antibodies to endocrine tissues were studied, bone mineral density of the forearm was measured by single photon densitometry, and information about the psychosocial distress of the patients was obtained. Adult height averaged 148.7 +/- 1.1 cm (mean +/- SE), which was 16 cm below the mean of adult women from a similar background. In Turner patients, final height correlated significantly with mid-parental height (final height = 0.67 x MPH + 32.1; r = 0.69). Body mass index was increased in Turner patients (25.6 +/- 1.3 kg/m2) compared to controls (21.4 +/- 0.6; P < 0.006). Six patients (25%) had impaired glucose tolerance or overt diabetes mellitus (one patient). Insulin release was augmented but delayed in the Turner group, and the area under the insulin stimulation curve was correlated to body mass index (r = +0.54, P < 0.01). Thyroid antibodies were detected in nine patients (37.5%). On average, bone density of the forearm was only marginally reduced compared to the age-dependent normal range. All women were employed, while only one of the Turner women was married. As a group, the subjects expressed greater distress due to infertility compared to short stature.(ABSTRACT TRUNCATED AT 250 WORDS)