Marco Guevara-Aguirre

Growth hormone receptor deficiency is associated with a major reduction in pro-aging signaling, cancer, and diabetes in humans.

Ecuadorians who have a genetic mutation in the growth hormone receptor almost never die of cancer or diabetes complications, possibly because of high resistance to oxidative damage and low circulating insulin. Clues to a Cancer- and Diabetes-Free Life In the 1958 film Live Fast and Die Young, two reckless sisters threaten to burn out early. Similarly, one theory of aging predicts that a faster metabolism leads to a shorter life. Does this trade-off also apply to age-related disease? A new study by Guevara-Aguirre et al. offers clues that address this seminal question. The authors’ findings stem from studies of a unique group of Ecuadorian people who have a mutation in the growth hormone receptor (GHR) gene and a resulting insulin-like growth factor–1 (IGF-1) deficiency, which stunts their growth. These descendants of Spanish conversos, Jews who converted to Christianity to avoid the Inquisition, almost never get diabetes or cancer as a result, the authors postulate, of the privileged metabolic status that arises from their altered hormonal state. Relative to controls, these subjects show lower insulin concentrations and higher insulin sensitivity, and when stressed, their cells tend to self-destruct rather than accumulate mutations and DNA damage—all features that are known to promote cell protection in model organisms. For 22 years, this group of 99 related Ecuadorians—most of whom are homozygous for an A-to-G splice site mutation at position 180 in exon 6 of the GHR gene—has been monitored extensively, so that their health details are well documented. From this reservoir of data, plus information about the diseases of family members as well as causes of death of those relatives who have died, the authors deciphered that the Ecuadorian subjects who carried the GHR mutation had an abnormally low incidence of cancer and diabetes. The group showed only one case of nonlethal cancer and no cases of diabetes, whereas the controls—unaffected relatives—developed cancer (17%) and diabetes (5%) at rates similar to those of the Ecuadorian population as a whole. To illuminate the underlying reason for the subjects’ freedom from these diseases, the authors focused on the components carried in their blood. In experiments on cultured human epithelial cells, Guevara-Aguirre et al. found that low concentrations of one of these, IGF-1, was responsible for preventing oxidative DNA damage when the cells were exposed to the oxidizing agent H2O2 and for promoting cell death when stress-related DNA damage did occur, a checkpoint that averts cancer-promoting behavior by abnormal cells. Analysis of the participating cell signaling pathways identified activation of the transcription factor FoxO under conditions of low IGF-1 as a likely mediator of these effects. Further, the lower blood insulin concentrations and higher insulin sensitivity in these subjects likely account for the absence of diabetes in this population. Although it is difficult to prove that alterations in IGF-1 amounts are responsible for the cancer- and diabetes-free lives of these Ecuadorian people, genetic work from several model organisms suggests that this is so. In yeast, mutations in genes that encode components of a growth-promoting pathway protect against age-dependent genomic instability, and mutations in the insulin/IGF-1–like signaling pathway increase life span and reduce abnormal cellular proliferation in worms. Mice with defects in GH and IGF-1 live exceptionally long lives, with delayed appearance of age-dependent mutations and cancer. The Ecuadorians do not live longer-than-normal lives compared with their compatriots, but rather die in due course from causes of death other than cancer and diabetes complications. Thus, the metabolic inverse of “live fast and die young”—a slowed metabolism yields a longer life—is not supported by the current findings. But a life free from two dreaded diseases may be considered a desirable trade-off. Mutations in growth signaling pathways extend life span, as well as protect against age-dependent DNA damage in yeast and decrease insulin resistance and cancer in mice. To test their effect in humans, we monitored for 22 years Ecuadorian individuals who carry mutations in the growth hormone receptor (GHR) gene that lead to severe GHR and IGF-1 (insulin-like growth factor–1) deficiencies. We combined this information with surveys to identify the cause and age of death for individuals in this community who died before this period. The individuals with GHR deficiency exhibited only one nonlethal malignancy and no cases of diabetes, in contrast to a prevalence of 17% for cancer and 5% for diabetes in control subjects. A possible explanation for the very low incidence of cancer was suggested by in vitro studies: Serum from subjects with GHR deficiency reduced DNA breaks but increased apoptosis in human mammary epithelial cells treated with hydrogen peroxide. Serum from GHR-deficient subjects also caused reduced expression of RAS, PKA (protein kinase A), and TOR (target of rapamycin) and up-regulation of SOD2 (superoxide dismutase 2) in treated cells, changes that promote cellular protection and life-span extension in model organisms. We also observed reduced insulin concentrations (1.4 μU/ml versus 4.4 μU/ml in unaffected relatives) and a very low HOMA-IR (homeostatic model assessment–insulin resistance) index (0.34 versus 0.96 in unaffected relatives) in individuals with GHR deficiency, indicating higher insulin sensitivity, which could explain the absence of diabetes in these subjects. These results provide evidence for a role of evolutionarily conserved pathways in the control of aging and disease burden in humans.

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.

The impact of Converso Jews on the genomes of modern Latin Americans

Modern day Latin America resulted from the encounter of Europeans with the indigenous peoples of the Americas in 1492, followed by waves of migration from Europe and Africa. As a result, the genomic structure of present day Latin Americans was determined both by the genetic structure of the founding populations and the numbers of migrants from these different populations. Here, we analyzed DNA collected from two well-established communities in Colorado (33 unrelated individuals) and Ecuador (20 unrelated individuals) with a measurable prevalence of the BRCA1 c.185delAG and the GHR c.E180 mutations, respectively, using Affymetrix Genome-wide Human SNP 6.0 arrays to identify their ancestry. These mutations are thought to have been brought to these communities by Sephardic Jewish progenitors. Principal component analysis and clustering methods were employed to determine the genome-wide patterns of continental ancestry within both populations using single nucleotide polymorphisms, complemented by determination of Y-chromosomal and mitochondrial DNA haplotypes. When examining the presumed European component of these two communities, we demonstrate enrichment for Sephardic Jewish ancestry not only for these mutations, but also for other segments as well. Although comparison of both groups to a reference Hispanic/Latino population of Mexicans demonstrated proximity and similarity to other modern day communities derived from a European and Native American two-way admixture, identity-by-descent and Y-chromosome mapping demonstrated signatures of Sephardim in both communities. These findings are consistent with historical accounts of Jewish migration from the realms that comprise modern Spain and Portugal during the Age of Discovery. More importantly, they provide a rationale for the occurrence of mutations typically associated with the Jewish Diaspora in Latin American communities.

A Novel Variant in CDKN1C Is Associated With Intrauterine Growth Restriction, Short Stature, and Early-Adulthood-Onset Diabetes

CONTEXT CDKN1C, a cyclin-dependent kinase inhibitor and negative regulator of cellular proliferation, is paternally imprinted and has been shown to regulate β-cell proliferation. CDKN1C mutations are associated with growth disorders, including Beckwith-Wiedemann syndrome and IMAGe syndrome. OBJECTIVE To investigate the genetic basis for a familial disorder characterized by intrauterine growth restriction, short stature, and early-adulthood-onset diabetes. DESIGN, SETTING, AND PARTICIPANTS Genomic DNA samples (15 affected and 26 unaffected from a six-generation pedigree) were analyzed by genome-wide single nucleotide polymorphism arrays, whole exome and Sanger sequencing, and multiplex ligation-dependent probe amplification. MAIN OUTCOME MEASURE(S) Subjects were assessed for height, weight, adrenal gland size, ACTH, diabetes status, and testis volume. Linkage and sequence analyses were performed, and the identified genetic variant was functionally evaluated in reconstitution studies. RESULTS The pedigree followed a paternally imprinted pattern of inheritance, and genetic linkage analysis identified a single significant 2.6-megabase locus on chromosome 11p15, within the imprinting center region 2. Multiplex ligation-dependent probe amplification did not detect copy number variants or methylation abnormalities. Whole exome sequencing revealed a single novel variant in the proliferating cell nuclear antigen-binding region of CDKN1C (c.842G>T, p.R281I) that co-segregated with affected status and, unlike variants found in IMAGe, did not entirely abrogate proliferating cell nuclear antigen binding. Clinical assessments revealed that affected individuals had low testicular volume but normal adrenal function. CONCLUSIONS We report a novel CDKN1C mutation associated with features of IMAGe syndrome, but without adrenal insufficiency or metaphyseal dysplasia, and characterized by early-adulthood-onset diabetes. Our data expand the range of phenotypes observed with CDKN1C defects and suggest that CDKN1C mutations may represent a novel monogenic form of diabetes.

Recommended IGF-I Dosage Causes Greater Fat Accumulation and Osseous Maturation Than Lower Dosage and May Compromise Long-term Growth Effects

CONTEXT The maximum dose of IGF-I recommended for treatment of GH insensitivity is commonly used. OBJECTIVE The aim was to test the hypothesis that a lower dose is as effective as a high dose of IGF-I in growth promotion and has fewer deleterious effects. DESIGN AND SETTING Subjects were treated for 3 years with regular examinations including bone age and dual energy x-ray absorptiometry and for 1 year with abdominal ultrasound studies at a clinical research institute in Quito, Ecuador. SUBJECTS The study included 21 subjects ages 3.2-15.9 years with GH insensitivity due to the same splice site mutation on the GH receptor gene. INTERVENTIONS Subjects were allocated to receive 120 (n = 14) or 80 (n = 7) μg/kg IGF-I twice daily. MAIN OUTCOME MEASURES Height velocity, osseous maturation, height SD scores (SDS), body composition, abdominal organ growth, and side effects were assessed. RESULTS There were no differences in growth velocity or height SDS increment by dosage, and the SDS increase was greater than in other reported series. Osseous maturation over 3 years with the high dose was nearly twice as rapid as with the lower dose (P < .001) and correlated with an increase in percentage body fat (r = .64; P < .001) and with adrenal size increase over 1 year (r = .32; P = .03). The ratio of bone age to height age was lower in the high-dose group after 3 years of treatment (P = .007). CONCLUSIONS The commonly used IGF-I dosage of 120 μg/kg twice a day is excessive in comparison to a dose of 80 μg/kg twice a day, disproportionately accelerating osseous maturation, probably from the combined effects of obesity and inappropriate adrenal growth, thus likely compromising adult height potential. Moreover, the lower dose decreases direct treatment cost by one-third.

Absence of hypoglycemia in response to varying doses of recombinant human insulin-like growth factor-I (rhIGF-I) in children and adolescents with low serum concentrations of IGF-I

AIM To determine whether recombinant human insulin-like growth factor-I (rhIGF-I) administration to children with low IGF-I and relatively low insulin-like growth factor binding protein-3 (IGFBP3) serum concentrations would result in hypoglycemia. METHODS Eighteen children age 11-19 y with serum levels of IGF-I< -2 SDS and IGFBP3< 0 SDS were randomly assigned to receive rhIGF-I at 80 microg/kg body weight daily (n = 6), 40 microg/kg twice daily (n = 6), or 80 microg/kg twice daily (n = 6). After a 10-d dose escalation and 15 d of treatment at the specified dosage, a 25-h pharmacokinetic/pharmacodynamic profile was obtained, which included 22 blood glucose measurements. Regular meals and snacks were provided. RESULTS No signs or symptoms of hypoglycemia were noted throughout the study. There were no differences in mean blood glucose concentrations among the three dosage groups. The lowest glucose value recorded, 3.44 mmol/l, was 15 min after a morning injection of 80 microg/kg IGF-I, and promptly rose. Although subjects were selected on the basis of low concentrations of IGF-I to represent proposed candidates for rhIGF-I therapy, the mean and range of SDS for height were not different from those of previously studied normal Ecuadorian controls. CONCLUSION In normal individuals with low serum concentrations of IGF-I and relatively low concentrations of IGFBP3, the administration of therapeutic doses of rhIGF-I, while maintaining reasonable food intake, does not result in hypoglycemia.

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.

Intrauterine and postnatal growth failure with normal GH/IGF1 axis and insulin-resistant diabetes in a consanguineous kinship.

OBJECTIVE To describe the clinical and biochemical features, and perform molecular analysis for candidate abnormalities in a novel familial syndrome of intrauterine growth retardation (IUGR), failure of an adolescent growth spurt with proportional adult short stature, minimal subluxation of the 5th metacarpal-phalangeal joint, and adult-onset insulin-resistant diabetes unrelated to obesity or other manifestations of metabolic syndrome (MS). DESIGN Detailed clinical history, auxological, biochemical, radiological, and molecular studies, including DNA analysis and in vitro study of the GH/IGF1 pathway. MATERIALS AND METHODS Ten affected adults from two generations of five related families were studied in detail, and information obtained about nine other likely affected individuals. RESULTS Height Z-scores ranged from -7.3 to -3.8. Unaffected parents of the older generation and frequency of confirmed and suspected instances of the syndrome in the two generations studied is consistent with autosomal recessive inheritance. Insulin resistance was uniformly present in seven subjects tested who were not taking insulin. Diabetes severity did not correlate with overweight. Subjects did not have other typical manifestations of MS such as substantial hyperlipidemia, osteoporosis, or hypertension. No biochemical abnormality in the GH/IGF1 axis or molecular defect was found. CONCLUSIONS While the association of IUGR and adult MS, including diabetes, has been well documented, these subjects did not have typical manifestations of MS. Abnormalities in common components that could result in a combination of IUGR, severe postnatal growth, and insulin resistance have been ruled out. A mutation in an unidentified gene may affect intrauterine and postnatal growth, with insulin resistance directly affected or as a result of this growth phenomenon.

Absence of hypoglycemia in response to varying doses of recombinant human insulin-like growth factor-I (rhIGF-I) in children and adolescents with low serum concentrations of IGF-I: Absence of hypoglycemia with rhIGF-I administration

Aim: To determine whether recombinant human insulin‐like growth factor‐I (rhIGF‐I) administration to children with low IGF‐I and relatively low insulin‐like growth factor binding protein‐3 (IGFBP3) serum concentrations would result in hypoglycemia. Methods: Eighteen children age 11–19 y with serum levels of IGF‐I < − 2 SDS and IGFBP3 < 0 SDS were randomly assigned to receive rhIGF‐I at 80 µg/kg body weight daily (n=6), 40 µg/kg twice daily (n=6), or 80 µg/kg twice daily (n=6). After a 10‐d dose escalation and 15 d of treatment at the specified dosage, a 25‐h pharmacokinetic/pharmacodynamic profile was obtained, which included 22 blood glucose measurements. Regular meals and snacks were provided. Results: No signs or symptoms of hypoglycemia were noted throughout the study. There were no differences in mean blood glucose concentrations among the three dosage groups. The lowest glucose value recorded, 3.44 mmol/l, was 15 min after a morning injection of 80 µg/kg IGF‐I, and promptly rose. Although subjects were selected on the basis of low concentrations of IGF‐I to represent proposed candidates for rhIGF‐I therapy, the mean and range of SDS for height were not different from those of previously studied normal Ecuadorian controls.