Significance of Direct Confirmation of Growth Hormone Insensitivity for the Diagnosis of Primary IGF-I Deficiency

Involvement of Sirtuin 1 in the Growth Hormone/Insulin-like Growth Factor 1 Signal Transduction and Its Impact on Growth Processes in Children

The regulation of growth processes in children depends on the synthesis of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Insulin-like growth factor 1, which is mainly secreted in the liver in response to GH, is the main peripheral mediator of GH action. Newly discovered factors regulating GH secretion and its effects are being studied recently. One of them is sirtuin 1 (SIRT1). This NAD+-dependent deacetylase, by modulating the JAK2/STAT pathway, is involved in the transduction of the GH signal in hepatocytes, leading to the synthesis of IGF-1. In addition, it participates in the regulation of the synthesis of GHRH in the hypothalamus and GH in the somatotropic cells. SIRT1 is suggested to be involved in growth plate chondrogenesis and longitudinal bone growth as it has a positive effect on the epiphyseal growth plate. SIRT1 is also implicated in various cellular processes, including metabolism, cell cycle regulation, apoptosis, oxidative stress response, and DNA repair. Thus, its expression varies depending on the different metabolic states. During malnutrition, SIRT1 blocks GH signal transduction in hepatocytes to reduce the IGF-1 secretion and prevent hypoglycemia (i.e., it causes transient GH resistance). In this review, we focused on the influence of SIRT1 on GH signal transduction and the implications that may arise for growth processes in children.

Inclusion and Withdrawal Criteria for Growth Hormone (GH) Therapy in Children with Idiopathic GH Deficiency—Towards Following the Evidence but Still with Unresolved Problems

According to current guidelines, growth hormone (GH) therapy is strongly recommended in children and adolescents with GH deficiency (GHD) in order to accelerate growth rate and attain normal adult height. The diagnosis of GHD requires demonstration of decreased GH secretion in stimulation tests, below the established threshold value. Currently, GHD in children is classified as secondary insulin-like growth factor-1 (IGF-1) deficiency. Most children diagnosed with isolated GHD present with normal GH secretion at the attainment of near-final height or even in mid-puberty. The most important clinical problems, related to the diagnosis of isolated GHD in children and to optimal duration of rhGH therapy include: arbitrary definition of subnormal GH peak in stimulation tests, disregarding factors influencing GH secretion, insufficient diagnostic accuracy and poor reproducibility of GH stimulation tests, discrepancies between spontaneous and stimulated GH secretion, clinical entity of neurosecretory dysfunction, discrepancies between IGF-1 concentrations and results of GH stimulation tests, significance of IGF-1 deficiency for the diagnosis of GHD, and a need for validation IGF-1 reference ranges. Many of these issues have remained unresolved for 25 years or even longer. It seems that finding solutions to them should optimize diagnostics and therapy of children with short stature.

Growth response to growth hormone (GH) treatment in children with GH deficiency (GHD) and those with idiopathic short stature (ISS) based on their pretreatment insulin-like growth factor 1 (IGFI) levels and at diagnosis and IGFI increment on treatment

OBJECTIVES

Some idiopathic short stature (ISS) patients may have varying degrees of insulin-like growth factor 1 (IGFI) deficiency. Others with growth hormone deficiency (GHD) (peak GH < 7 ng/dL after provocation) have normal IGFI levels. Do children with ISS or those with GHD with variable pretreatment IGFI standard deviation score (IGFISDS) have different IGFI and growth responses to recombinant human growth hormone (rhGH) therapy?

METHODS

We studied the effect of GH therapy (0.035-0.06 mg/kg/day) on linear growth and weight gain per day (WGPD) in children with ISS (n=13) and those with GHD (n=10) who have low pretreatment IGFISDS (IGF SDS < -1.5) and compared them with age-matched prepubertal children with ISS (n=10) and GHD (n=17) who had normal pretreatment IGFISDS. An untreated group of children with ISS (n=12) served as a control group.

RESULTS

At presentation, the height standard deviation score (HtSDS) of children with ISS who had low pretreatment IGFISDS was significantly lower compared to the normal IGFI group. The age, body mass index (BMI), BMISDS, peak GH response to clonidine provocation and bone age did not differ between the two study groups. After 1 year of treatment with rhGH (0.035-0.06 mg/kg/day) IGFISDS increased significantly in both groups (p<0.05). Both had significantly increased HtSDS (catch-up growth). The increase in the HtSDS and WGPD were significantly greater in the lower pretreatment IGFISDS group. The IGFSDS, BMISDS, HtSDS and difference between HtSDS and mid-parental HtSDS were significantly greater in the rhGH treated groups vs. the not treated group. In the GHD groups (normal and low IGFISDS), after 1 year of GH therapy (0.03-0.05 mg/kg/day), the HtSDS increased significantly in both, (p<0.01). The WGPD and increment in BMI were significantly greater in children who had low pretreatment IGFISDS. There was a significant increase in the IGFSDS in the two treated groups (p<0.05), however, the WGPD was greater in the pretreatment low IGFISDS.

CONCLUSIONS

IGFI deficiency represents a low anabolic state. Correction of IGFI level (through rhGH and/or improved nutrition) in short children (ISS and GHD) was associated with increased linear growth and WGPD denoting significant effect on bone growth and muscle protein accretion.