MECHANISMS IN ENDOCRINOLOGY: Transient juvenile hypoglycemia in growth hormone receptor deficiency - mechanistic insights from Laron syndrome and tailored animal models.

The aim of the study is to find possible explanations for vanishing juvenile hypoglycemia in growth hormone receptor deficiency (GHRD) in human patients and animal models. We reviewed parameters of glucose metabolism in distinct age groups into two human cohorts (Israeli and Ecuadorian) of Laron syndrome (LS) patients, a mouse model (Ghr-KO mouse) and provided additional data for a porcine model (GHR-KO pig). Juvenile hypoglycemia is a common symptom of GHRD and vanishes in adulthood. In the Israeli cohort, developing metabolic syndrome is associated with decreasing insulin sensitivity, insulinopenia and glucose intolerance, and increasing glucose levels with age. In the Ecuadorian patients and both animal models, insulin sensitivity is preserved or even enhanced. Alterations in food intake and energy consumption do not explain the differences in glucose levels; neither is the accumulation of body fat associated with negative effects in the Ecuadorian cohort nor in the animal models. A reduced beta-cell mass and resulting insulin secretory capacity is common and leads to glucose intolerance in Ghr-KO mice, while glucose tolerance is preserved in Ecuadorian patients and the GHR-KO pig. In human patients and the GHR-KO pig, a simultaneous occurrence of normoglycemia with the onset of puberty is reported. Reduced gluconeogenesis in GHRD is discussed to cause juvenile hypoglycemia and a counter-regulatory stimulation of gluconeogenesis can be hypothesized. A coherent study assessing endogenous glucose production and beta-cell capacity in the hypoglycemic and normoglycemic age group is needed. This can be performed in GHR-KO pigs, including castrated animals.

Insights from the clinical phenotype of subjects with Laron syndrome in Ecuador.

The Ecuadorian cohort of subjects with LS has taught us valuable lessons since the late 80's. We have learned about migration of Sephardic Jews to our country, their isolation in remote hamlets and further inbreeding. These geographical, historical and social determinants induced dissemination of a growth hormone (GH) receptor mutation which widely occurred in those almost inaccessible villages. Consequently, the world's largest Laron syndrome (LS) cohort emerged in Loja and El Oro, two of the southern provinces of Ecuador. We have been fortunate to study these patients since 1987. New clinical features derived from GH insensitivity, their growth patterns as well as treatment with exogenous insulin-like growth factor I (IGF-I) have been reported. Novel biochemical characteristics in the field of GH insensitivity, IGFs, IGF binding proteins (BP) and their clinical correlates have also been described. In the last few years, studies on the morbidity and mortality of Ecuadorian LS adults surprisingly demonstrated that despite obesity, they had lower incidence of diabetes and cancer than their relatives. These events were linked to their metabolic phenotype of elevated but ineffective GH concentrations and low circulating IGF-I and IGFBP-3. It was also noted that absent GH counter-regulation induces a decrease in insulin resistance (IR), which results in low but highly efficient insulin levels which properly handle metabolic substrates. We propose that the combination of low IGF-I signaling, decreased IR, and efficient serum insulin concentrations are reasonable explanations for the diminished incidence of diabetes and cancer in these subjects.

Insulin resistance depends on GH counter-regulation in two syndromes of short stature.

Specific phenotypic features of subjects affected with genetic syndromes depend on peculiarities of expression of each discrete mutation and on extent of its divergence from normal physiology. In this context, and when studying the GH/IGF-I axis of subjects with two different syndromes that include severe short stature (SSS), we noticed different metabolic phenotypes in each cohort. Subjects with Laron syndrome (LS), who have GH insensitivity (GHI), display obesity, increased body fat, enhanced insulin sensitivity and diminished incidence of diabetes mellitus. Subjects with a new syndrome (NS), who have normal GH signaling, display intrauterine growth retardation (IUGR), normal to slightly elevated body fat content, insulin resistance and early onset type 2 diabetes mellitus (T2DM). In consequence, we were able to observe the clinical consequences of different GH counter-regulation status on carbohydrate metabolism, especially considering that subjects with either syndrome most likely have diminished pancreatic reserve.

Despite higher body fat content, Ecuadorian subjects with Laron syndrome have less insulin resistance and lower incidence of diabetes than their relatives.

In the present pandemics of obesity and insulin resistant diabetes mellitus (DM), the specific contribution of etiological factors such as shifts in nutritional and exercise patterns, genetic and hormonal, is subject of ongoing research. Among the hormonal factors implicated, we selected obesity-driven insulin resistance for further evaluation. It is known that growth hormone (GH) has profound effects on carbohydrate metabolism. In consequence, we compared the effects of the lack of the counter-regulatory effects of GH, in a group of subjects with GH receptor deficiency (GHRD) due to a mutated GH receptor vs. that of their normal relatives. It was found that, despite their obesity, subjects with GHRD, have diminished incidence of diabetes, lower glucose and insulin concentrations, and lower values of indexes indicative of insulin resistance such as HOMA-IR. The GHRD subjects were also capable of appropriately handling glucose or mixed meal loads despite diminished insulin secretion. These observations allow us to suggest that the association of obesity with increased risk for diabetes appears to be dependent on intact growth hormone signaling.

Fifty seven years of follow-up of the Israeli cohort of Laron Syndrome patients-From discovery to treatment.

Clinical and laboratory investigations of dwarfed children newly Jewish immigrants from Yemen and Middle East and who resembled patients with isolated growth hormone deficiency were started by our group in 1958. In 1963 when we found that they have high serum levels of hGH, we knew that we had discovered a new disease of primary GH insensitivity. It was subsequently coined Laron Syndrome (LS, OMIM #262500). The etiopathogenesis was disclosed by 2 liver biopsies demonstrating a defect in the GH receptor. Subsequent investigations demonstrated deletions or mutations in the GHR gene. The defect lead to an inability of IGF-I generation, resulting in severe dwarfism, obesity, and other morphologic and biochemical pathologies due to IGF-I deficiency. With the biosynthesis of IGF-I in 1986, therapeutic trials started. Following closely our cohort of 69 patients with LS enabled us to study its features in untreated and IGF-I treated patients. This syndrome proved to be a unique model to investigate the effects of IGF-I dissociated from GH stimulation. In recent studies we found that homozygous patients for the GHR mutations are protected lifelong from developing malignancies, opening new directions of research.

GH Receptor Deficiency in Ecuadorian Adults Is Associated With Obesity and Enhanced Insulin Sensitivity.

CONTEXT: Ecuadorian subjects with GH receptor deficiency (GHRD) have not developed diabetes, despite obesity. OBJECTIVE: We sought to determine the metabolic associations for this phenomenon. DESIGN: Four studies were carried out: 1) glucose, lipid, adipocytokine concentrations; 2) metabolomics evaluation; 3) metabolic responses to a high-calorie meal; and 4) oral glucose tolerance tests. SETTING: Clinical Research Institute in Quito, Ecuador. SUBJECTS: Adults homozygous for the E180 splice mutation of the GH receptor (GHRD) were matched for age, gender, and body mass index with unaffected control relatives (C) as follows: study 1, 27 GHRD and 35 C; study 2, 10 GHRD and 10 C; study 3, seven GHRD and 11 C; and study 4, seven GHRD and seven C. RESULTS: Although GHRD subjects had greater mean percentage body fat than controls, their fasting insulin, 2-hour blood glucose, and triglyceride levels were lower. The indicator of insulin sensitivity, homeostasis model of assessment 2%S, was greater (P < .0001), and the indicator of insulin resistance, homeostasis model of assessment 2-IR, was lower (P = .0025). Metabolomic differences between GHRD and control subjects were consistent with their differing insulin sensitivity, including postprandial decreases of branched-chain amino acids that were more pronounced in controls. High molecular weight and total adiponectin concentrations were greater in GHRD (P = .0004 and P = .0128, respectively), and leptin levels were lower (P = .02). Although approximately 65% the weight of controls, GHRD subjects consumed an identical high-calorie meal; nonetheless, their mean glucose concentrations were lower, with mean insulin levels one-third those of controls. Results of the 2-hour oral glucose tolerance test were similar. MAIN OUTCOME MEASURES: Measures of insulin sensitivity, adipocytokines, and energy metabolites. CONCLUSIONS: Without GH counter-regulation, GHRD is associated with insulin efficiency and obesity. Lower leptin levels, despite higher percentage body fat, suggest that obesity-associated leptin resistance is GH dependent. Elevated adiponectin levels not correlated with percentage body fat indicate that GH signaling is necessary for their typical suppression with obesity.

Obesity, diabetes and cancer: insight into the relationship from a cohort with growth hormone receptor deficiency.

Obesity with insulin-resistant diabetes and increased cancer risk is a global problem. We consider the alterations of metabolism attendant on the underlying pathogenic overnutrition and the role of the growth hormone (GH)-IGF-1 axis in this interaction. Obesity-induced insulin resistance is a determinant of diabetes. Excess glucose, and an elevated concentration of insulin acting through its own receptors along with complex interactions with the IGF-1 system, will add extra fuel and fuel signalling for malignant growth and induce anti-apoptotic activities, permitting proliferation of forbidden clones. In Ecuador there are ~100 living adults with lifelong IGF-1 deficiency caused by a GH receptor (GHR) mutation who, despite a high percentage of body fat, have markedly increased insulin sensitivity compared with age- and BMI-matched control relatives, and no instances of diabetes, which is present in 6% of unaffected relatives. Only 1 of 20 deceased individuals with GHR deficiency died of cancer vs 20% of ~1,500 relatives. Fewer DNA breaks and increased apoptosis occurred in cell cultures exposed to oxidant agents following addition of serum from GHR-deficient individuals vs serum from control relatives. These changes were reversible by adding IGF-1 to the serum from the GHR-deficient individuals. The reduction in central regulators of pro-ageing signalling thus appears to be the result of an absence of GHR function. The complex inter-relationship of obesity, diabetes and cancer risk is related to excess insulin and fuel supply, in the presence of heightened anti-apoptosis and uninhibited DNA damage when GHR function is normal.

GH deficiency in adult B-thalassemia major patients and its relationship with IGF-1 production.

Endocrine complications in Β-thalassemia represent a prominent cause of morbidity. Above all, dysfunction of GH-IGF-1 axis is of a major concern because of its pathogenic role on cardiac and bone disease, frequently described in this clinical setting. The aim of this paper is to analyze GH-IGF-1 axis in a cohort of 25 adult patients affected by Β-thalassemia. We found that GH deficiency was present in only 8% of our patients if diagnosis was based on GH peak below 9µg/L to two GH provocative tests instead of only one, and was mainly related to iron overload. On the contrary, IGF-1 production was impaired in a higher percentage of patients (72%), without significant correlation with iron burden. Of note, patients with hepatitis C virus infection showed lower IGF-1 concentrations than uninfected subjects despite a normal GH reserve, suggesting that partial GH insensitivity at the post-receptor level may play a key role in IGF-1 deficiency described in thalassemic patients.

Growth hormone and adrenal response to intramuscular glucagon test and its relationship to IGF-1 production and left ventricular ejection fraction in adult B-thalassemia major patients.

In patients with b-thalassemia major (TM), the anterior pituitary gland is particularly sensitive to free radical stresses. It has been reported that the GH deficiency (GHD) may be secondary to either pituitary or hypothalamic dysfunction. The duration of the disease, the patient's age and the severity of iron overload are the most important factors responsible for the defect of growth hormone (GH) secretion. Recent reports have documented a frequency of severe growth hormone deficiency in 13%-32% of patients with b-thalassemia major. All of these patients underwent GH-releasing hormone (GH-RH) plus arginine (ARG) testing. We undertook the present study to evaluate the GH and adrenal response during glucagon stimulation test (GST) in patients with TM because the GH-RH plus ARG test in patients with hypothalamic GHD may be misleading. Thirty-three adult TM patients were recruited (mean age 36.6 years). Fifty four percent were included in the severe GHD group (GH peak below 3mg/l). The IGF-1 level in TM patients was consistently low (60.3 ± 35.3 mg/l) and 86.6% of patients with a normal GH response to GST had a low IGF-1 level. These findings are also indicative of a relative resistance to GH. In eight out of 18 TM patients (44.4%), the GHD was associated with hypogonadotropic hypogonadism. A positive correlation was found between GH peak after GST and IGF-1 level (r = 0.8, p: 0.003) and a negative correlation between the age of female TM patients and GH peak (r = 0.711, p: 0.007). All patients but one had no evidence of cardiac iron overload (mean T2* 30.4 ± 8.2 ms; range 14-44 ms). The mean LVEF (%) in TM patients was no different when compared to healthy controls. However, three patients with severe GHD and normal T2*were found to have reduced LVEF.One patient (4%) had a peak cortisol response to GST compatible to adrenal insufficiency. Nausea, headache and\or hypoglycemia occurred in 3 patients (12%) during GST. In conclusion, our study demonstrates that the presence of GHD is frequent in adult TM patients. According to the international guidelines for medical practice, we believe that before considering hormone replacement therapy, a second test to confirm the diagnosis of GHD and adrenal insufficiency is required.