Background
Department of Endocrinology and Internal Medicine and the medical research laboratories at Aar-hus University Hospital have a long tradition for clinical and translational investigations of meta-bolic effects of growth hormone (GH) and the interplay between GH, insulin, and the IGF-I system. This is a brief introduction to ongoing and previous projects within this and closely related fields of research.

GH, insulin sensitivity, metabolism, and puberty
Insulin sensitivity decreases by up to 50% during puberty. The hormonal basis for this decrease remains to be elucidated. Sex hormones and GH increase in puberty and GH stimulates linear growth and exerts a variety of important metabolic effects including lipolysis, inhibition of prote-olysis and maintenance of glucose homeostasis by increasing insulin resistance.

The molecular mechanisms causing insulin resistance in puberty
IGF-I levels decrease in GH deficiency. Adolescents with GH deficiency in puberty require increased doses of GH compared to prepubertal needs. Thus, putative hormonal candidates that induce in-sulin resistance in puberty include sex hormones, GH or a combination of sex hormones and GH. Moreover, it is of interest to investigate the effect of increased GH levels on insulin resistance, protein synthesis, and metabolism in puberty.

Children and adolescents with type 1 diabetes
Measurement of C-peptide levels has demonstrated that some children and adults with long-lasting type 1 diabetes (T1D) have retained the ability to produce minor amounts of insulin. This residual insulin secretion is far from being sufficient to maintain normoglycemia, and these indi-viduals are therefore in the need of exogenous insulin, i.e. they are treated as non-insulin-producing patients with T1D. However, we have data indicating that even a minute endogenous secretion of insulin may be import. Thus, our studies have demonstrated that pre-pubertal as well as adult patients with T1D and C-peptide positive have levels of insulin-like growth factor I (IGF-I) closer to normal values than what is observed in matched C-peptide negative patients. Although the clinical significance of this finding remains unknown, a normalised IGF-I action is likely to be beneficial. Firstly, this may improve insulin sensitivity, secondly, a normalised IGF-I may have beneficial effects when it comes to the development of late-diabetic complications (1,2).

Insulin treatment of patients with T1D; long-acting human insulin vs. insulin analogues
The novel long-acting insulin analogues differ from human insulin in their pharmaco-kinetic and dynamic properties. So far, novel long-acting analogues are primarily compared by their ability to produce stable and safe blood glucose levels. By contrast, only little data is available on their non-glycemic effects.
We recently compared insulin Detemir (Leveir®), insulin Glargine (Lantus®) and NPH-insulin (Insu-latard®) in adults with T1D. Our data suggested that Levemir® was more liver-specific than Lantus® and Insulatard®, as Levemir® affected liver-specific peptides belonging to the IGF system. Of no-tice, these changes were not mirrored by the effects of the three long-acting insulins on blood glucose levels. Thus, our findings suggest that non-glycemic effects may differ between different insulin analogues. We are currently investigating this in further detail (3).

Assay developments at the medical research laboratory
Throughout the years, the researchers at the medical research laboratory have contributed to the development and clinical validation of numerous novel assays, in particular within the GH - IGF field. We were the first to describe and validate assays for free, unbound IGF-I (4), bioactive IGF-I (5) and free GH (6). Furthermore, researchers at the laboratory have been involved in preparing the consensus statement that describes how GH and IGF-I should be measured in clinical samples.

Turner Syndrome, Klinefelter Syndrome and other rare diseases
Turner Syndrome is a condition with hypogonadism, reduced final height and a host of other medical conditions, like congenital heart defects. The effect of GH and female hormone replace-ment therapy on these aspects is poorly delineated. Infertility is almost always present and is poorly understood. Klinefelter syndrome, 47,XXX and 47,XYY are also focus points for research, where we aim at integrating endocrinology, cardiology, genetics and epidemiology.

Study of children born to mothers with type 1 diabetes
Over the last 20 years our knowledge concerning the diabetes in pregnancy has increased. How-ever, the long-term consequences of being born to a mother with pregestational type 1 diabetes are still unclear. Especially later risk of developing diabetes, obesity and cognitive impairment in offspring has been debated. As part of the national EPICOM project we cooperate with Rigshospi-talet and Odense University Hospital in establishing a unique cohort of children born to women with type 1 diabetes and matched controls from the background population. We have used this cohort to study risk of developing diabetes and obesity and the mechanisms behind this in off-spring.

Endocrine follow-up of patients with Prader Willi Syndrome (PWS)
PWS is caused by a chromosome disorder involving the paternal short arm of chromosome 15. The prevalence is approximately 1:25,000. Intellectual impairment, conductive aspects and neuromus-cular abnormities characterize the syndrome. PWS patients also present with partial GH deficiency and frequent hypogonadism. Department of Endocrinology and Internal Medicine and the medical research laboratories have been collaborating with other centers nationally and with Scandinavian investigations on the effect of GH substitution therapy in adolescents and adults with PWS.

Ongoing projects
GH, insulin sensitivity, metabolism, and puberty
We are currently performing a clinical, placebo controlled, randomized study on adolescents in Tanner stage II – IV with GH deficiency and healthy matched controls. The aim is to investigate the effect of GH and IGF-I on insulin sensitivity, protein metabolism and acyl ghrelin levels in puberty.

Turner Syndrome and Klinefelter syndrome
Turner Syndrome: A five-year randomized project with adolescents treated with either 2 mg es-tradiol or 4 mg estradiol (+ gestagen) to study the effects on aorta, bones and the internal female reproductive system. Epidemiological studies are ongoing where we aim at elucidating morbidity, mortality and medicine use.

Study of children born to mothers with type 1 diabetes
The EPICOM study is a national study that aims to investigate children born to women with type 1 diabetes during pregnancy. The participants are children born to women with type 1 diabetes be-tween 1993 and 1999 and matched controls from the background population. Study 1: A clinical follow-up study of participant risk of diabetes and cardiovascular disease, body mass index, body composition, puberty development and intelligence. Study 2: Register based study regarding mor-tality, morbidity and use of prescription medication. Study 3: Using epigenetic characterization (methylation status and long-non-coding RNA) the molecular consequences of being born to a mother with type 1 diabetes is examined.

PWS patients
In collaboration with the Centre for Rare Diseases a cohort of patients with PWS are systematically followed up. A detailed study on the adipose tissue distribution is being planned.

Milestones – important publications
GH, insulin sensitivity, metabolism, and puberty
Status 'recruiting'.

Turner Syndrome and other syndromes characterized by sex chromosome disorders
Research in Turner Syndrome has resulted in an extensive list of publications in international jour-nals; please see the complete reference list below.

Methods
GH, insulin sensitivity, metabolism, and puberty
• Clinical, controlled cross-over study
• Stable isotope amino acid technique to assess whole body protein turnover
• Hyperinsulinemic euglycemic clamp technique

Turner Syndrome and other syndromes characterized by sex chromosome disorders
Epidemiology, endocrinology, genetics, and genomic medicine.

Study of children born to mothers with type 1 diabetes
• Epidemiological study including data from the Danish National Hospital Register, Statistics Denmark, Danish Register of Causes of Death, the National Cancer Registry, Danish Psychi-atric Hospital Register, the Danish National Prescription Registry and the Danish Diabetes Association.
• Clinical examination including cognitive tests.
• Genetic and epigenetic techniques at the Department of Molecular Metabolism (MOMA)

PWS patients
Tracer methods to assess lipid metabolism

The IGF-I system
Development of new methods to determine mechanisms regulating the IGF-I system in vivo.

Important international collaborators
GH, insulin sensitivity, metabolism, and puberty
Michael O. Thorner, Bruce Gaylinn og Ralph Nass, University of Virginia Health System, Charlottes-ville, Virginia, USA

Turner Syndrome and other syndromes characterized by sex chromosome disorders
Outi Hovatta, Karolinska, Stockholm; Ephraim Gutmark, University of Cincinnati, USA

PWS
Charlotte Høybye, Karolinska Hospital, Stockholm

References
1. Hedman CA, Frystyk J, Lindström T, Chen JW, Flyvbjerg A, Ørskov H, Arnqvist HJ. Residual beta-cell function more than glycemic control determines abnormalities of the insulin-like growth factor system in type 1 diabetes. Journal of Clinical Endocrinology Metabolism 2004; 89:6305-6309

2. Sorensen JS, Birkebaek NH, Bjerre M, Pociot F, Kristensen K, Hoejberg AS, Frystyk J, Danish Society for Diabetes in C, Adolescence. Residual beta-cell function and the insulin-like growth factor system in Danish children and adolescents with type 1 diabetes. J Clin Endocrinol Metab 2014:jc20143521
3. Ma Z, Christiansen JS, Laursen T, Lauritzen T, Frystyk J. Short-term effects of NPH insulin, insulin detemir, and insulin glargine on the GH-IGF1-IGFBP axis in patients with type 1 diabetes. Eur J Endocrinol 2014; 171:471-479
4. Frystyk J, Skjærbæk C, Dinesen B, Ørskov H. Free insulin-like growth factors (IGF-I and IGF-II) in human serum. FEBS Lett 1994; 348:185-191
5. Chen JW, Ledet T, Ørskov H, Jessen N, Lund S, Whittaker J, De Meyts P, Larsen MB, Christiansen JS, Frystyk J. A highly sensitive and specific assay for determination of IGF-I bioactivity in human serum. American Journal of Physiology - Endocrinology and Metabolism 2003; 284:E1149-E1155
6. Frystyk J, Andreasen CM, Fisker S. Determination of free growth hormone. Journal of Clinical Endocrinology Metabolism 2008; 93:3008-3014

Most important publications on Turner Syndrome:
• Cleemann L, Mortensen KH, Holm K, Smedegaard H, Skouby SO, Wieslander SB, Leffers AM, Leth-Espensen, Pedersen EM, Gravholt CH: Aortic dimensions in girls and young women with Turner syndrome – a magnetic resonance imaging study. Pediatr Cardiol, 31:497-504,
• Ottesen AM, Aksglaede L, Garn I, Tartaglia N, Tassone F, Gravholt CH, Bojesen A, Sørensen K, Jørgensen N, Rajpert–De Meyts E, Gerdes T, Lind A-M, Kjaergaard S, Juul A: Increased number of sex chromsomes affect height in a non-linear fashion: a study of 305 patients with sex chromosome aneuploidy. Am J Med Genet, 152A:1206-1212, 2010.
• Stochholm K, Juul S, Gravholt CH: Diagnosis and mortality in 47,XYY persons: a registry study. Orphanet J Rare Dis, 5:15, 2010.
• Hagen C, Aksglæde L, Sørensen K, Main KM, Boas M, Cleemann L, Holm K, Gravholt CH, Andersson A-M, Pedersen AT, Pedersen JH, Linneberg A, Jørgensen T, Kjaergaard S, Juul A: Serum levels of anti-Müllerian hormone as a marker of ovarian function in 926 healthy fe-males from birth to adulthood and in 172 Turner syndrome patients. J Clin Endocrinol Me-tab, 95:5003-5010, 2010.
• Cleemann L, Holm K, Fallentin E, Skouby SO, Smedegaard H, Møller N, Borch-Christensen H, Jeppesen EM, Andersson AM, Cohen A, Gravholt CH: Uterus and ovaries in girls and young women with Turner syndrome evaluated by ultrasound and magnetic resonance imaging. Clin Endocrinol, 74:756-761, 2011.
• Cleemann L, Holm K, Kobbernagel H, Skouby SO, Kristensen B, Smedegaard H, Andersson AM, Cohen A, Gravholt CH: Normal tempo of bone formation in Turner syndrome despite signs of accelerated bone resorption. Horm Res Pediatr, 76:193-201, 2011.
• Stochholm K, Juul S, Gravholt CH: Socio-economic status factors affect mortality in 47,XYY – a comparison with the background population and Klinefelter syndrome. Am J Med Genet, 158A:2421-2429, 2012.
• Stochholm K, Juul S, Christiansen JS, Gravholt CH: Mortality and socio-economic status in adults with childhood onset GH deficiency (GHD) is highly dependent on the primary cause of GHD. Eur J Endocrinol, 167:663-670, 2012.
• Mortensen KH, Andersen NH, Gravholt CH: Cardiovascular phenotype in Turner syndrome – integrating genetics, cardiology and endocrinology. Endocr Rev, 33:677-714,
• Groth KA, Jensen AS, Høst A, Gravholt CH, Bojesen A: Klinefelter syndrome – a clinical up-date. J Clin Endocrinol Metab, 98:20-30, 2013.