Severe short stature caused by novel compound heterozygous mutations of the insulin-like growth factor 1 receptor (IGF1R)

Early IGF-1 receptor inhibition in mice mimics preterm human brain disorders and reveals a therapeutic target

Besides recent advances in neonatal care, preterm newborns still develop sex-biased behavioral alterations. Preterms fail to receive placental insulin-like growth factor-1 (IGF-1), a major fetal growth hormone in utero, and low IGF-1 serum levels correlate with preterm poor neurodevelopmental outcomes. Here, we mimicked IGF-1 deficiency of preterm newborns in mice by perinatal administration of an IGF-1 receptor antagonist. This resulted in sex-biased brain microstructural, functional, and behavioral alterations, resembling those of ex-preterm children, which we characterized performing parallel mouse/human behavioral tests. Pharmacological enhancement of GABAergic tonic inhibition by the U.S. Food and Drug Administration-approved drug ganaxolone rescued functional/behavioral alterations in mice. Establishing an unprecedented mouse model of prematurity, our work dissects the mechanisms at the core of abnormal behaviors and identifies a readily translatable therapeutic strategy for preterm brain disorders.

Damaging missense variants in IGF1R implicate a role for IGF-1 resistance in the etiology of type 2 diabetes

Type 2 diabetes (T2D) is a heritable metabolic disorder. While population studies have identified hundreds of common genetic variants associated with T2D, the role of rare (frequency < 0.1%) protein-coding variation is less clear. We performed exome sequence analysis in 418,436 (n = 32,374 T2D cases) individuals in the UK Biobank. We identified previously reported genes (GCK, GIGYF1, HNF1A) in addition to missense variants in ZEB2 (n = 31 carriers; odds ratio [OR] = 5.5 [95% confidence interval = 2.5-12.0]; p = 6.4 × 10^-7), MLXIPL (n = 245; OR = 2.3 [1.6-3.2]; p = 3.2 × 10^-7), and IGF1R (n = 394; OR = 2.4 [1.8-3.2]; p = 1.3 × 10^-10). Carriers of damaging missense variants within IGF1R were also shorter (-2.2 cm [-1.8 to -2.7]; p = 1.2 × 10^-19) and had higher circulating insulin-like growth factor-1 (IGF-1) protein levels (2.3 nmol/L [1.7-2.9]; p = 2.8 × 10^-14), indicating relative IGF-1 resistance. A likely causal role of IGF-1 resistance was supported by Mendelian randomization analyses using common variants. These results increase understanding of the genetic architecture of T2D and highlight the growth hormone/IGF-1 axis as a potential therapeutic target.

Components of IGF-axis in growth disorders: a systematic review and patent landscape report

PURPOSE

In this review, epi/genetic mutations of IGF-axis components associated with growth disorders have been summarized alongwith assessment of relevant diagnostic and therapeutic technology through patent literature.

METHODOLOGY

PROSPERO protocol registration CRD42021279468. For scientific literature search Literature databases (PubMed, EMBASE, ScienceDirect, and Google Scholar) were queried using the appropriate syntax. Various filters were applied based on inclusion and exclusion criteria. Search results were further refined by two authors for finalizing studies to be included in this synthesis. For patent documents search Patent databases (Patentscope and Espacenet) were queried using keywords: IGF or IGFBP. Filters were applied according to International Patent Classification (IPC) and Cooperative Patent Classification (CPC). Search results were reviewed by two authors for inclusion in the patent landscape report.

RESULTS

For scientific literature analysis, out of 545 search results, 196 were selected for review based on the inclusion criteria. For Patent literature search, out of 485 results, 37 were selected for this synthesis.

CONCLUSION

Dysregulation of IGF-axis components leads to various abnormalities and their key role in growth and development suggests epi/mutations or structural defects among IGF-axis genes can be associated with growth disorders and may explain some of the idiopathic short stature cases. Trend of patent filings indicate advent of recombinant technology for therapeutics.

Mutations in GHR and IGF1R Genes as a Potential Reason for the Lack of Catch-Up Growth in SGA Children

The aim of this review was to describe all of the mutations in the growth hormone receptor (GHR) and insulin-like growth factor-1 receptor (IGF1R) genes that have been discovered so far, and their possible impact on final body height, as well as their relationship with catch-up growth in children born small for gestational age (SGA). Mutations in the GHR gene were found to cause a body height below −2 SD, from the mean for sex and age, whereas the mutations in the IGF1R gene were associated with low body height and intrauterine growth restriction (IUGR), and with being born SGA. After birth, when the child’s growth is not restricted by the intrauterine environment, the infant may develop its developmental potential and experience catch-up growth, which makes it possible to catch up with peers born appropriate for gestational age (AGA). Despite this, catch-up growth does not apply to all, but only to about 85% of SGA children, and its mechanism is unknown. It is possible that SGA children who did not experience catch-up growth are carriers of mutations in the GHR and/or IGF1R genes

Diagnosis of Chromosome 15q-Terminal Deletion Syndrome through Elevated Fasting Serum Growth Hormone Levels

Chromosome 15q26-qter deletion syndrome is a rare disease that causes prenatal and postnatal growth retardation, microcephaly, developmental delay, and congenital heart diseases, mainly due to haploinsufficiency of IGF1R. In addition, patients with pathogenic variants of the IGF1R show similar symptoms. We report the case of a 5-month-old girl with prenatal and postnatal growth retardation, microcephaly, and congenital heart disease. At 5 months of age, her length was 54.7 cm (−4.3 SD), her weight was 4.4 kg (−3.1 SD), and her head circumference was 37.4 cm (−2.8 SD), thus presenting severe growth retardation. Repeated pre-feeding serum GH levels were abnormally high (26.1–85.5 ng/mL), and IGF-1 levels (+0.16 to +1.2 SD) were relatively high. The 15q sub-telomere fluorescence in situ hybridization analysis revealed a heterozygous deletion in the 15q terminal region. Whole-genome single nucleotide polymorphism microarray analysis showed a terminal deletion of 6.4 Mb on 15q26.2q26.3. This is the first report showing that fasting GH levels are high in early infancy in patients with IGF1R abnormalities. In addition to relatively high IGF-1 levels, elevated fasting GH levels in early infancy may contribute to the diagnosis of IGF1R abnormalities.

IGF1R is a mediator of sex-specific metabolism in mice: Effects of age and high-fat diet

OBJECTIVE

We aimed to investigate the short and long-term metabolic consequences of IGF1R systemic gene deficiency in mice.

METHODS

UBC-CreERT2, Igf1r^fl/fl mutant mice were used to suppress IGF1R signaling in adult tissues by inducing postnatal generalized Igf1r deletion with tamoxifen. Animals were analyzed at two different ages: i) 13-weeks old young mice, and ii) 12-months old middle-aged mice. In addition, the effects of 10 weeks-long high-fat diet (HFD) were investigated in middle-aged mice.

RESULTS

Young IGF1R-deficient mice were insulin-resistant, with high IGF1, growth hormone (GH) and IGFBP3, as well as low IGFBP2 circulating levels. Males also presented increased triglycerides in liver. In contrast, middle-aged mice did not clearly show all of these alterations, suggesting possible compensatory effects. Middle-aged IGF1R-deficient male mice were able to counteract the negative effects induced by aging and HFD in adiposity, inflammation and glucose metabolism. A metabolic sexual dimorphism dependent on IGF1R was observed, especially in middle-aged mice.

CONCLUSIONS

These results demonstrate that IGF1R is involved in metabolic homeostasis, with effects modulated by diet-induced obesity and aging in a sex dependent manner. Thus, IGF1R deficiency in mice is proposed as a useful tool to understand metabolic alterations observed in patients with IGF1R gene deletions.

Novel Insights Into the Genetic Causes of Short Stature in Children

Short stature is a common reason for consulting a growth specialist during childhood. Normal height is a polygenic trait involving a complex interaction between hormonal, nutritional and psychosocial components. Genetic factors are becoming very important in the understanding of short stature. After exclusion of the most frequent causes of growth failure, clinicians need to evaluate whether a genetic cause might be taken into consideration. In fact, genetic causes of short stature are probably misdiagnosed during clinical practice and the underlying cause of short stature frequently remains unknown, thus classifying children as having idiopathic short stature (ISS). However, over the past decade, novel genetic techniques have led to the discovery of novel genes associated with linear growth and thus to the ability to define new possible aetiologies of short stature. In fact, thanks to the newer genetic advances, it is possible to properly re-classify about 25–40% of children previously diagnosed with ISS. The purpose of this article is to describe the main monogenic causes of short stature, which, thanks to advances in molecular genetics, are assuming an increasingly important role in the clinical approach to short children.

Genotype-Structure-Phenotype Correlations of Disease-Associated IGF1R Variants and Similarities to Those of INSR Variants

We previously reported genotype-phenotype correlations in 12 missense variants causing severe insulin resistance, located in the second and third fibronectin type III (FnIII) domains of the insulin receptor (INSR), containing the α-β cleavage and part of insulin-binding sites. This study aimed to identify genotype-phenotype correlations in FnIII domain variants of IGF1R, a structurally related homolog of INSR, which may be associated with growth retardation, using the recently reported crystal structures of IGF1R. A structural bioinformatics analysis of five previously reported disease-associated heterozygous missense variants and a likely benign variant in the FnIII domains of IGF1R predicted that the disease-associated variants would severely impair the hydrophobic core formation and stability of the FnIII domains or affect the α-β cleavage site, while the likely benign variant would not affect the folding of the domains. A functional analysis of these variants in CHO cells showed impaired receptor processing and autophosphorylation in cells expressing the disease-associated variants but not in those expressing the wild-type form or the likely benign variant. These results demonstrated genotype-phenotype correlations in the FnIII domain variants of IGF1R, which are presumably consistent with those of INSR and would help in the early diagnosis of patients with disease-associated IGF1R variants.

Genetic causes of growth hormone insensitivity beyond GHR

Growth hormone insensitivity (GHI) syndrome, first described in 1966, is classically associated with monogenic defects in the GH receptor (GHR) gene which result in severe post-natal growth failure as consequences of insulin-like growth factor I (IGF-I) deficiency. Over the years, recognition of other monogenic defects downstream of GHR has greatly expanded understanding of primary causes of GHI and growth retardation, with either IGF-I deficiency or IGF-I insensitivity as clinical outcomes. Mutations in IGF1 and signaling component STAT5B disrupt IGF-I production, while defects in IGFALS and PAPPA2, disrupt transport and release of circulating IGF-I, respectively, affecting bioavailability of the growth-promoting IGF-I. Defects in IGF1R, cognate cell-surface receptor for IGF-I, disrupt not only IGF-I actions, but actions of the related IGF-II peptides. The importance of IGF-II for normal developmental growth is emphasized with recent identification of defects in the maternally imprinted IGF2 gene. Current application of next-generation genomic sequencing has expedited the pace of identifying new molecular defects in known genes or in new genes, thereby expanding the spectrum of GH and IGF insensitivity. This review discusses insights gained and future directions from patient-based molecular and functional studies.

Genetic IGF1R defects: new cases expand the spectrum of clinical features

PURPOSE

We aimed to identify the phenotypic variability of IGF1R defects in a cohort of short children with normal GH secretion gathered through the last decade.

PATIENTS AND METHODS

Fifty children (25 girls) with short stature and a basal/stimulated growth hormone (GH) over 10 ng/ml having either a low birth weight or microcephaly were enrolled. MLPA and then Sanger sequence analysis were performed to detect IGF1R defects. The auxological and metabolic evaluation were carried out in index cases and their first degree family members whenever available.

RESULTS

A total of seven (14%) IGF1R defects were detected. Two IGF1R deletions and five heterozygous variants (one frameshift, four missense) were identified. Three (likely) pathogenic, one VUS and one likely benign were classified by using ACMG. All children with IGF1R defects had a height < - 2.5SDS, birth weight < - 1.4SDS, and head circumference < - 1.36SDS. IGF-1 ranged from - 2.44 to 2.13 SDS. One child with a 15q terminal deletion had a normal phenotype and intelligence, whereas low IQ is a finding in a case with missense variant. Two parents who carried IGF1R mutations had diabetes mellitus, hypertension and hyperlipidemia, one of whom also had hypergonadotropic hypogonadism.

CONCLUSION

We found a deletion or variant in IGF1R in 14% of short children. Birth weight, head circumference, intelligence, dysmorphic features, IGF-1 levels and even height are not consistent among patients. Additionally, metabolic and gonadal complications may appear during adulthood, suggesting that patients should be followed into adulthood to monitor for these late complications.

Disorders of IGFs and IGF-1R signaling pathways

The insulin-like growth factor (IGF) system comprises two ligands, IGF-I and IGF-II, that regulate multiple physiological processes, including mammalian development, metabolism and growth, through the type 1 IGF receptor (IGF-1R). The growth hormone (GH)-IGF-I axis is the major regulator of longitudinal growth. IGF-II is expressed in many tissues, notably the placenta, to regulate human pre- and post-natal growth and development. This review provides a brief introduction to the IGF system and summarizes findings from reports arising from recent larger genomic sequencing studies of human genetic mutations in IGF1 and IGF2 and genes of proteins regulating IGF action, namely the IGF-1R, IGF-1R signaling pathway components and the IGF binding proteins (IGFBPs). A perspective on the effect of homozygous mutations on structure and function of the IGFs and IGF-1R is also given and this is related to the effects on growth.

A Novel Mutation in Insulin-Like Growth Factor 1 Receptor (c.641-2A>G) Is Associated with Impaired Growth, Hypoglycemia, and Modified Immune Phenotypes

INTRODUCTION

Insulin-like growth factor 1 receptor (IGF1R) mutations lead to systemic disturbances in growth and glucose homeostasis due to widespread IGF1R expression throughout the body. IGF1R is expressed by innate and adaptive immune cells, facilitating their development and exerting immunomodulatory roles in the periphery.

CASE PRESENTATION

We report on a family presenting with a novel heterozygous IGF1R mutation with characterization of the mutation, IGF1R expression, and immune phenotyping. Twin probands presented clinically with short stature and hypoglycemia. Variable phenotypic expression was seen in 2 other family members carrying the IGF1R mutation. The probands were treated with exogenous growth hormone therapy and dietary cornstarch, improving linear growth and reducing hypoglycemic events. IGF1R c.641-2A>G caused abnormal mRNA splicing and premature protein termination. Flow cytometric immunophenotyping demonstrated lower IGF1R on peripheral blood mononuclear cells from IGF1R c.641-2A>G subjects. This alteration was associated with reduced levels of T-helper 17 cells and a higher percentage of T-helper 1 cells compared to controls, suggesting decreased IGF1R expression may affect CD4+ Th-cell lineage commitment.

DISCUSSION

Collectively, these data suggest a novel loss-of-function mutation (c.641-2A>G) leads to aberrant mRNA splicing and IGF1R expression resulting in hypoglycemia, growth restriction, and altered immune phenotypes.

Insulin resistance and exaggerated insulin sensitivity triggered by single-gene mutations in the insulin signaling pathway

Whereas the genetic basis of insulin sensitivity is determined by variation in multiple genes, mutations of single genes can give rise to profound changes in such sensitivity. Mutations of the insulin receptor gene (INSR)-which trigger type A insulin resistance, Rabson-Mendenhall, or Donohue syndromes-and those of the gene for the p85α regulatory subunit of phosphoinositide 3-kinase (PIK3R1), which give rise to SHORT syndrome, are the most common and second most common causes, respectively, of single-gene insulin resistance. Loss-of-function mutations of the genes for the protein kinase Akt2 (AKT2) or for TBC1 domain family member 4 (TBC1D4) have been identified in families with severe insulin resistance. Gain-of-function mutations of the gene for protein tyrosine phosphatase nonreceptor type 11 (PTPN11), which negatively regulates insulin receptor signaling, give rise to Noonan syndrome, and some individuals with this syndrome manifest insulin resistance. Gain-of-function mutations of the gene for the p110α catalytic subunit of phosphoinositide 3-kinase (PIK3CA) have been identified in individuals with segmental overgrowth or megalencephaly, some of whom also manifest spontaneous hypoglycemia. A gain-of-function mutation of AKT2 was also found in individuals with recurrent hypoglycemia. Loss-of-function mutations of the gene for phosphatase and tensin homolog (PTEN), another negative regulator of insulin signaling, give rise to Cowden syndrome in association with exaggerated metabolic actions of insulin. Clinical manifestations of individuals with such mutations of genes related to insulin signaling thus provide insight into the essential function of such genes in the human body.

A Comprehensive Cohort Analysis Comparing Growth and GH Therapy Response in IGF1R Mutation Carriers and SGA Children

CONTEXT

IGF1 receptor mutations (IGF1RM) are rare; however, patients exhibit pronounced growth retardation without catch-up. Although several case reports exist, a comprehensive statistical analysis investigating growth profile and benefit of recombinant human growth hormone (rhGH) treatment is still missing.

OBJECTIVE AND METHODS

Here, we compared IGF1RM carriers (n = 23) retrospectively regarding birth parameters, growth response to rhGH therapy, near final height, and glucose/insulin homeostasis to treated children born small for gestational age (SGA) (n = 34). Additionally, health profiles of adult IGF1RM carriers were surveyed by a questionnaire.

RESULTS

IGF1RM carriers were significantly smaller at rhGH initiation and had a diminished first-year response compared to SGA children (Δ height standard deviation score: 0.29 vs. 0.65), resulting in a lower growth response under therapy. Interestingly, the number of poor therapy responders was three times higher for IGF1RM carriers than for SGA patients (53 % vs. 17 %). However, most IGF1RM good responders showed catch-up growth to the levels of SGA patients. Moreover, we observed no differences in homeostasis model assessment of insulin resistance before treatment, but during treatment insulin resistance was significantly increased in IGF1RM carriers compared to SGA children. Analyses in adult mutation carriers indicated no increased occurrence of comorbidities later in life compared to SGA controls.

CONCLUSION

In summary, IGF1RM carriers showed a more pronounced growth retardation and lower response to rhGH therapy compared to non-mutation carriers, with high individual variability. Therefore, a critical reevaluation of success should be performed periodically. In adulthood, we could not observe a significant influence of IGF1RM on metabolism and health of carriers.

Role of thyroid hormones in craniofacial development

The development of the craniofacial skeleton relies on complex temporospatial organization of diverse cell types by key signalling molecules. Even minor disruptions to these processes can result in deleterious consequences for the structure and function of the skull. Thyroid hormone deficiency causes delayed craniofacial and tooth development, dysplastic facial features and delayed development of the ossicles in the middle ear. Thyroid hormone excess, by contrast, accelerates development of the skull and, in severe cases, might lead to craniosynostosis with neurological sequelae and facial hypoplasia. The pathogenesis of these important abnormalities remains poorly understood and underinvestigated. The orchestration of craniofacial development and regulation of suture and synchondrosis growth is dependent on several critical signalling pathways. The underlying mechanisms by which these key pathways regulate craniofacial growth and maturation are largely unclear, but studies of single-gene disorders resulting in craniofacial malformations have identified a number of critical signalling molecules and receptors. The craniofacial consequences resulting from gain-of-function and loss-of-function mutations affecting insulin-like growth factor 1, fibroblast growth factor receptor and WNT signalling are similar to the effects of altered thyroid status and mutations affecting thyroid hormone action, suggesting that these critical pathways interact in the regulation of craniofacial development.

Intrauterine Twin Discordancy and Partial Postnatal Catch-up Growth in a Girl with a Pathogenic IGF1R Mutation

OBJECTIVE

Insulin like growth factors-1 (IGF-1) is essential for normal in utero and postnatal human growth. It mediates its effects through the IGF-1 receptor (IGF1R), a widely expressed cell surface tyrosine kinase receptor. The aim of the study was to analyze pre- and post-natal growth, clinical features and laboratory findings in a small for gestational age (SGA) girl in whom discordant postnatal growth persisted and her appropriate for gestational age (AGA) brother.

METHODS

A girl born with a low weight and length [-2.3 and -2.4 standard deviation (SD) score (SDS), respectively] but borderline low head circumference (-1.6 SD) presented with a height of -1.7 SDS, in contrast to a normal height twin brother (0.0 SDS). IGF-1 resistance was suspected because of elevated serum IGF-1 levels.

RESULTS

Sequencing revealed the presence of a previously described pathogenic heterozygous mutation (p.Glu1050Lys) in the SGA girl which was not present in the parents nor in the AGA twin brother.

CONCLUSION

The pathogenic IGF1R mutation in this girl led to intrauterine growth retardation followed by partial postnatal catch-up growth. Height in mid-childhood was in the lower half of the reference range, but still 1.7 SD shorter than her twin brother.

Phenotypic Features and Response to GH Treatment of Patients With a Molecular Defect of the IGF-1 Receptor

CONTEXT

The phenotype and response to GH treatment of children with an IGF1R defect is insufficiently known.

OBJECTIVE

To develop a clinical score for selecting children with short stature for genetic testing and evaluate the efficacy of treatment.

DESIGN AND SETTING

Case series with an IGF1R defect identified in a university genetic laboratory.

PATIENTS AND INTERVENTIONS

Of all patients with sufficient clinical data, 18 had (likely) pathogenic mutations (group 1) and 7 had 15q deletions including IGF1R (group 2); 19 patients were treated with GH.

MAIN OUTCOME MEASURES

Phenotype and response to GH treatment.

RESULTS

In groups 1 and 2, mean (range) birth weight, length, and head circumference (HC) SD scores (SDSs) were -2.1 (-3.7 to -0.4), -2.7 (-5.0 to -1.0), and -1.6 (-3.0 to 0.0), respectively. At presentation, height, HC, and serum IGF-1 SDSs were -3.0 (-5.5 to -1.7), -2.5 (-4.2 to -0.5), and +1.2 (-1.3 to 3.2), respectively. Feeding problems were reported in 15 of 19 patients. A clinical score with 76% sensitivity is proposed. After 3 years of GH treatment [1.1 (0.2) mg/m2/d] height gain in groups 1 (n = 12) and 2 (n = 7) was 0.9 SDS and 1.3 SDS (at a mean IGF-1 of 3.5 SDS), less than reported for small for gestational age (1.8 SDS).

CONCLUSION

A clinical score encompassing birth weight and/or length, short stature, microcephaly, and IGF-1 is useful for selecting patients for IGF1R analysis. Feeding problems are common and the growth response to GH treatment is moderate.

In vitro epidermis model mimicking IGF-1-specific age-related decline

Ageing is a complex multifaceted process affecting skin functionality and structure. Several 3D organotypic skin culture models have reproduced ageing by inducing replicative senescence, glycation or oxidative stress. Yet, very few models have focused on hormonal ageing and especially the insulin-like growth factor 1 (IGF-1) signalling pathway, which has been associated with longevity in animal studies and is necessary for the early stages of skin development. In this study, we built an organotypic epidermis model with targeted IGF-1 receptor knockdown to reproduce some aspects of hormonal ageing on skin. Our model displayed morphological and functional features of aged epidermis, which were mostly attributed to a loss of function of the Stratum basale. IGF-1 receptor knockdown keratinocytes depicted an extended cell cycle, reduced proliferation potential and reduced adhesion capacities and greater sensitivity to oxidative stress than control cells. Altogether, this model represents an essential tool for further investigations into the mechanisms linked to some aspects of hormonal decline or when screening for potent anti-ageing compounds.

Targeted Searches of the Electronic Health Record and Genomics Identify an Etiology in Three Patients with Short Stature and High IGF-I Levels

INTRODUCTION

Short stature is one of the most common reasons for referral to a pediatric endocrinologist and can result from many etiologies. However, many patients with short stature do not receive a definitive diagnosis.

OBJECTIVE

To ascertain whether integrating targeted bioinformatics searches of electronic health records (EHRs) combined with genomic studies could identify patients with previously undiagnosed rare genetic etiologies of short stature. We focused on a specific rare phenotypic subgroup: patients with short stature and elevated IGF-I levels.

METHODS

We performed a cross-sectional cohort study at three large academic pediatric healthcare networks. Eligible subjects included children with heights below -2 SD, IGF-I levels >90th percentile, and no known etiology for short stature. We performed a search of the EHRs to identify eligible patients. Patients were then recruited for phenotyping followed by exome sequencing and in vitro assays of IGF1R function.

RESULTS

A total of 234 patients were identified by the bioinformatics algorithm with 39 deemed eligible after manual review (17%). Of those, 9 were successfully recruited. A genetic etiology was identified in 3 of the 9 patients including 2 novel variants in IGF1R and a de novo variant in CHD2. In vitro studies supported the pathogenicity of the IGF1R variants.

CONCLUSIONS

This study provides proof of principle that patients with rare phenotypic subgroups can be identified based on discrete data elements in the EHRs. Although limitations exist to fully automating this approach, these searches may help find patients with previously unidentified rare genetic disorders.

IGF1R Gene Alterations in Children Born Small for Gestitional Age (SGA)

BACKGROUND:

Small for gestational age (SGA)-born children are a heterogeneous group with few genetic causes reported. Genetic alterations in the IGF1 receptor (IGF1R) are found in some SGA children.

AIM:

To investigate whether alterations in IGF1R gene are present in SGA born children.

PATIENTS AND METHODS:

We analysed 64 children born SGA who stayed short (mean -3.25 ± 0.9 SDS) within the first 4 years of age, and 36 SGA children who caught up growth (0.20 ± 1.1 SDS). PCR products of all coding IGF1R exons were screened by dHPLC followed by direct sequencing of conspicuous fragments to identify small nucleotide variants. The presence of IGF1R gene copy number alterations was determined by Multiplex Ligation-dependent Probe Amplification (MLPA).

RESULTS:

The cohort of short SGA born children revealed a heterozygous, synonymous variant c.3453C > T in one patient and a novel heterozygous 3 bp in-frame deletion (c.3234_3236delCAT) resulting in one amino acid deletion (p.Ile1078del) in another patient. The first patient had normal serum levels of IGF1. The second patient had unusually low IGF1 serum concentrations (-1.57 SD), which contrasts previously published data where IGF1 levels rarely are found below the age-adjusted mean.

CONCLUSIONS:

IGF1R gene alterations were present in 2 of 64 short SGA children. The patients did not have any dysmorphic features or developmental delay. It is remarkable that one of them had significantly decreased serum concentrations of IGF1. Growth response to GH treatment in one of the patients was favourable, while the second one discontinued the treatment, but with catch-up growth.

IGF1R Variants in Patients With Growth Impairment: Four Novel Variants and Genotype-Phenotype Correlations

OBJECTIVE

IGF1R gene mutations have been associated with varying degrees of intrauterine and postnatal growth retardation, as well as microcephaly. Both autosomal-dominant and autosomal-recessive inheritance patterns have been reported. This study aimed to analyze the IGF1R gene in children with growth impairment using whole-exome sequencing (WES) and assess the clinical features with the autosomal-dominant and autosomal-recessive models.

METHODS

We performed WES in 28 unrelated patients and found three children harboring IGF1R gene variants. We compared the clinical findings in our cases carrying IGF1R mutations to those in patients reported in the Human Gene Mutation Database (HGMD).

RESULTS

We identified four IGF1R gene variations by WES in three unrelated patients, including one missense variant [c.3740T>C (p.M1247T)] (patient 1) inherited from an affected mother, one missense variant [c.744T>G (p.C248W)] (patient 2) inherited from an affected father, and two compound heterozygous variations [c.2305G>C (p.E769Q) and c.2684G>A (p.R895Q)] (patient 3). To date, 22 patients have been described as harboring pathogenic variations in IGF1R in the HGMD. We found that patients with compound heterozygous or homozygous variations displayed more severe phenotypes that were mainly characterized by developmental and speech delays, as well as mental retardation.

CONCLUSION

We identified four pathogenic variations in the IGF1R gene, which expanded the known mutation spectrum. Through a comparison among patients with reported IGF1R pathogenic variations, this study determined that an autosomal-recessive inheritance model of the IGF1R gene may result in a more severe phenotype with developmental and speech delays, as well as mental retardation.

Mechano-growth factor protects against mechanical overload induced damage and promotes migration of growth plate chondrocytes through RhoA/YAP pathway

Epiphyseal growth plate is highly dynamic tissue which is controlled by a variety of endocrine, paracrine hormones, and by complex local signaling loops and mechanical loading. Mechano growth factor (MGF), the splice variant of the IGF-I gene, has been discovered to play important roles in tissue growth and repair. However, the effect of MGF on the growth plate remains unclear. In the present study, we found that MGF mRNA expression of growth plate chondrocytes was upregulated in response to mechanical stimuli. Treatment of MGF had no effect on growth plate chondrocytes proliferation and differentiation. But it could inhibit growth plate chondrocytes apoptosis and inflammation under mechanical overload. Moreover, both wound healing and transwell assay indicated that MGF could significantly enhance growth plate chondrocytes migration which was accompanied with YAP activation and nucleus translocation. Knockdown of YAP with YAP siRNA suppressed migration induced by MGF, indicating the essential role of YAP in MGF promoting growth plate chondrocytes migration. Furthermore, MGF promoted YAP activation through RhoA GTPase mediated cytoskeleton reorganization, RhoA inhibition using C3 toxin abrogated MGF induced YAP activation. Importantly, we found that MGF promoted focal adhesion(FA) formation and knockdown of YAP with YAP siRNA partially suppressed the activation of FA kinase, implying that YAP is associated with FA formation. In conclusion, MGF is an autocrine growth factor which is regulated by mechanical stimuli. MGF could not only protect growth plate chondrocytes against damage by mechanical overload, but also promote migration through activation of RhoA/YAP signaling axis. Most importantly, our findings indicate that MGF promote cell migration through YAP mediated FA formation to determine the FA-cytoskeleton remodeling.

Genetic disorders of GH action pathway

While insensitivity to GH (GHI) is characterized by low IGF-I levels, normal or elevated GH levels, and lack of IGF-I response to GH treatment, IGF-I resistance is characterized by elevated IGF-I levels with normal/high GH levels. Several genetic defects are responsible for impairment of GH and IGF-I actions resulting in short stature that could affect intrauterine growth or be present in the postnatal period. The genetic defects affecting GH and/or IGF-I action can be divided into five different groups: GH insensitivity by defects affecting the GH receptor (GHR), the intracellular GH signaling pathway (STAT5B, STAT3, IKBKB, IL2RG, PIK3R1), the synthesis of insulin-like growth factors (IGF1, IGF2), the transport/bioavailability of IGFs (IGFALS, PAPPA2), and defects affecting IGF-I sensitivity (IGF1R). Complete GH insensitivity (GHI) was first reported by Zvi Laron and his colleagues in patients with classical appearance of GH deficiency, but presenting elevated levels of GH. The association of GH insensitivity with several clinical sings of immune-dysfunction and autoimmune dysregulation are characteristic of molecular defects in the intracellular GH signaling pathway (STAT5B, STAT3, IKBKB, IL2RG, PIK3R1). Gene mutations in the IGF1 and IGF2 genes have been described in patients presenting intrauterine growth retardation and postnatal short stature. Molecular defects have also been reported in the IGFALS gene, that encodes the acid-labile subunit (ALS), responsible to stabilize circulating IGF-I in ternary complexes, and more recently in the PAPPA2 gen that encodes the pregnancy-associated plasma protein-A2, a protease that specifically cleaves IGFBP-3 and IGFBP-5 regulating the accessibility of IGFs to their target tissues. Mutations in the IGF1R gene resulted in IGF-I insensitivity in patients with impaired intrauterine and postnatal growth. These studies have revealed novel molecular mechanisms of GH insensitivity/primary IGF-I deficiency beyond the GH receptor gene. In addition, they have also underlined the importance of several players of the GH-IGF axis in the complex system that promotes human growth.

The Role of Insulin-Like Growth Factor 1 in the Progression of Age-Related Hearing Loss

Aging is associated with impairment of sensorial functions and with the onset of neurodegenerative diseases. As pari passu circulating insulin-like growth factor 1 (IGF-1) bioavailability progressively decreases, we see a direct correlation with sensory impairment and cognitive performance in older humans. Age-related sensory loss is typically caused by the irreversible death of highly differentiated neurons and sensory receptor cells. Among sensory deficits, age-related hearing loss (ARHL), also named presbycusis, affects one third of the population over 65 years of age and is a major factor in the progression of cognitive problems in the elderly. The genetic and molecular bases of ARHL are largely unknown and only a few genes related to susceptibility to oxidative stress, excitotoxicity, and cell death have been identified. IGF-1 is known to be a neuroprotective agent that maintains cellular metabolism, activates growth, proliferation and differentiation, and limits cell death. Inborn IGF-1 deficiency leads to profound sensorineural hearing loss both in humans and mice. IGF-1 haploinsufficiency has also been shown to correlate with ARHL. There is not much information available on the effect of IGF-1 deficiency on other human sensory systems, but experimental models show a long-term impact on the retina. A secondary action of IGF-1 is the control of oxidative stress and inflammation, thus helping to resolve damage situations, acute or made chronic by aging. Here we will review the primary actions of IGF-1 in the auditory system and the underlying molecular mechanisms.

A novel heterozygous IGF-1 receptor mutation associated with hypoglycemia

Mutation in the insulin-like growth factor-1 receptor (IGF1R) gene is a rare cause for intrauterine and postnatal growth disorders. Patients identified with IGF1R mutations present with either normal or impaired glucose tolerance. None of the cases described so far showed hypoglycemia. We aimed to identify the genetic basis for small for gestational age, short stature and hypoglycemia over three generations in one family. The proband, a 9-year-old male, presented in infancy with recurrent hypoglycemic episodes, symmetric intrauterine growth retardation and postnatal growth retardation. Blood DNA samples from the patient, his parents, a maternal sister and maternal grandmother underwent Sanger sequencing of the IGF1R gene. Primary skin fibroblast cultures of the patient, his mother and age- and sex-matched control donors were used for gene expression and receptor functional analyses. We found a novel heterozygous mutation (c.94 + 1g > a, D1105E) affecting the splicing site of the IGF1R mRNA in the patient, his mother and his grandmother. Primary fibroblast cultures derived from the patient and his mother showed reduced proliferation and impaired activation of the IGF1R, evident by reduced IGF1R and AKT phosphorylation upon ligand binding. In conclusion, the newly identified heterozygous missense mutation in exon 1 of IGF1R (D1105E) results in impaired IGF1R function and is associated with small for gestational age, microcephaly and abnormal glucose metabolism. Further studies are required to understand the mechanisms by which this mutation leads to hypoglycemia.

Expanding Genetic and Functional Diagnoses of IGF1R Haploinsufficiencies

BACKGROUND

The growth-promoting effects of IGF-I is mediated through the IGF-I receptor (IGF1R), a widely expressed cell-surface tyrosine kinase receptor. IGF1R copy number variants (CNV) can cause pre- and postnatal growth restriction or overgrowth.

METHODS

Whole exome sequence (WES), chromosomal microarray, and targeted IGF1R gene analyses were performed on 3 unrelated children who share features of small for gestational age, short stature, and elevated serum IGF-I, but otherwise had clinical heterogeneity. Fluorescence-activated cell sorting (FACS) analysis of cell-surface IGF1R was performed on live primary cells derived from the patients.

RESULTS

Two novel IGF1R CNV and a heterozygous IGF1R nonsense variant were identified in the 3 patients. One CNV (4.492 Mb) was successfully called from WES, utilizing eXome-Hidden Markov Model (XHMM) analysis. FACS analysis of cell-surface IGF1R on live primary cells derived from the patients demonstrated a ∼50% reduction in IGF1R availability associated with the haploinsufficiency state.

CONCLUSION

In addition to conventional methods, IGF1R CNV can be identified from WES data. FACS analysis of live primary cells is a promising method for efficiently evaluating and screening for IGF1R haploinsufficiency. Further investigations are necessary to delineate how comparable IGF1R availability leads to the wide spectrum of clinical phenotypes and variable responsiveness to rhGH therapy.

Involvement of Igf1r in Bronchiolar Epithelial Regeneration: Role during Repair Kinetics after Selective Club Cell Ablation

Regeneration of lung epithelium is vital for maintaining airway function and integrity. An imbalance between epithelial damage and repair is at the basis of numerous chronic lung diseases such as asthma, COPD, pulmonary fibrosis and lung cancer. IGF (Insulin-like Growth Factors) signaling has been associated with most of these respiratory pathologies, although their mechanisms of action in this tissue remain poorly understood. Expression profiles analyses of IGF system genes performed in mouse lung support their functional implication in pulmonary ontogeny. Immuno-localization revealed high expression levels of Igf1r (Insulin-like Growth Factor 1 Receptor) in lung epithelial cells, alveolar macrophages and smooth muscle. To further understand the role of Igf1r in pulmonary homeostasis, two distinct lung epithelial-specific Igf1r mutant mice were generated and studied. The lack of Igf1r disturbed airway epithelial differentiation in adult mice, and revealed enhanced proliferation and altered morphology in distal airway club cells. During recovery after naphthalene-induced club cell injury, the kinetics of terminal bronchiolar epithelium regeneration was hindered in Igf1r mutants, revealing increased proliferation and delayed differentiation of club and ciliated cells. Amid airway restoration, lungs of Igf1r deficient mice showed increased levels of Igf1, Insr, Igfbp3 and epithelial precursor markers, reduced amounts of Scgb1a1 protein, and alterations in IGF signaling mediators. These results support the role of Igf1r in controlling the kinetics of cell proliferation and differentiation during pulmonary airway epithelial regeneration after injury.

IGF-I deficiency, longevity and cancer protection of patients with Laron syndrome

Laron syndrome (LS) is a unique model of congenital IGF-I deficiency. It is characterized by dwarfism and obesity, and is caused by deletion or mutations of the growth hormone receptor (GH-R) gene. It is hypothesized that LS is an old disease originating in Indonesia and that the mutated gene spread to South Asia, the Middle East, the Mediterranean region and South America.

MECHANISMS IN ENDOCRINOLOGY: Novel genetic causes of short stature

The fast technological development, particularly single nucleotide polymorphism array, array-comparative genomic hybridization, and whole exome sequencing, has led to the discovery of many novel genetic causes of growth failure. In this review we discuss a selection of these, according to a diagnostic classification centred on the epiphyseal growth plate. We successively discuss disorders in hormone signalling, paracrine factors, matrix molecules, intracellular pathways, and fundamental cellular processes, followed by chromosomal aberrations including copy number variants (CNVs) and imprinting disorders associated with short stature. Many novel causes of GH deficiency (GHD) as part of combined pituitary hormone deficiency have been uncovered. The most frequent genetic causes of isolated GHD are GH1 and GHRHR defects, but several novel causes have recently been found, such as GHSR, RNPC3, and IFT172 mutations. Besides well-defined causes of GH insensitivity (GHR, STAT5B, IGFALS, IGF1 defects), disorders of NFκB signalling, STAT3 and IGF2 have recently been discovered. Heterozygous IGF1R defects are a relatively frequent cause of prenatal and postnatal growth retardation. TRHA mutations cause a syndromic form of short stature with elevated T3/T4 ratio. Disorders of signalling of various paracrine factors (FGFs, BMPs, WNTs, PTHrP/IHH, and CNP/NPR2) or genetic defects affecting cartilage extracellular matrix usually cause disproportionate short stature. Heterozygous NPR2 or SHOX defects may be found in ∼3% of short children, and also rasopathies (e.g., Noonan syndrome) can be found in children without clear syndromic appearance. Numerous other syndromes associated with short stature are caused by genetic defects in fundamental cellular processes, chromosomal abnormalities, CNVs, and imprinting disorders.

A New Homozygous IGF1R Variant Defines a Clinically Recognizable Incomplete Dominant form of SHORT Syndrome

Here, we describe a child, born from consanguineous parents, with clinical features of SHORT syndrome, high IGF1 levels, developmental delay, CNS defects, and marked progeroid appearance. By exome sequencing, we identified a new homozygous c.2201G>T missense mutation in the IGF1R gene. Proband's parents and other relatives, all heterozygous carriers of the mutation, presented with milder phenotype including high IGFI levels, short stature, and type 2 diabetes. Functional studies using patient's cell lines showed a lower IGF1R expression that leads to the alteration of IGF1R-mediated PI3K/AKT/mTOR downstream pathways, including autophagy. This study defines a clinically recognizable incomplete dominant form of SHORT syndrome, and provides relevant insights into the pathophysiological and phenotypical consequences of IGF1R mutations.

Regulation of body growth

PURPOSE OF REVIEW

Recent basic studies have yielded important new insights into the molecular mechanisms that regulate growth locally. Simultaneously, clinical studies have identified new molecular defects that cause growth failure and overgrowth, and genome-wide association studies have elucidated the genetic basis for normal human height variation.

RECENT FINDINGS

The Hippo pathway has emerged as one of the major mechanisms controlling organ size. In addition, an extensive genetic program has been described that allows rapid body growth in the fetus and infant but then causes growth to slow with age in multiple tissues. In human genome-wide association studies, hundreds of loci associated with adult stature have been identified; many appear to involve genes that function locally in the growth plate. Clinical genetic studies have identified a new genetic abnormality, microduplication of Xq26.3, that is responsible for growth hormone excess, and a gene, DNMT3A, in which mutations cause an overgrowth syndrome through epigenetic mechanisms.

SUMMARY

These recent advances in our understanding of somatic growth not only provide insight into childhood growth disorders but also have broader medical applications because disruption of these regulatory systems contributes to oncogenesis.

Insulin-Like Growth Factor-Independent Effects of Growth Hormone on Growth Plate Chondrogenesis and Longitudinal Bone Growth

GH stimulates growth plate chondrogenesis and longitudinal bone growth directly at the growth plate. However, it is not clear yet whether these effects are entirely mediated by the local expression and action of IGF-1 and IGF-2. To determine whether GH has any IGF-independent growth-promoting effects, we generated (TamCart)Igf1r(flox/flox) mice. The systemic injection of tamoxifen in these mice postnatally resulted in the excision of the IGF-1 receptor (Igf1r) gene exclusively in the growth plate. (TamCart)Igf1r(flox/flox) tamoxifen-treated mice [knockout (KO) mice] and their Igf1r(flox/flox) control littermates (C mice) were injected for 4 weeks with GH. At the end of the 4-week period, the tibial growth and growth plate height of GH-treated KO mice were greater than those of untreated C or untreated KO mice. The systemic injection of GH increased the phosphorylation of Janus kinase 2 and signal transducer and activator of transcription 5B in the tibial growth plate of the C and KO mice. In addition, GH increased the mRNA expression of bone morphogenetic protein-2 and the mRNA expression and protein phosphorylation of nuclear factor-κB p65 in both C and KO mice. In cultured chondrocytes transfected with Igf1r small interfering RNA, the addition of GH in the culture medium significantly induced thymidine incorporation and collagen X mRNA expression. In conclusion, our findings demonstrate that GH can promote growth plate chondrogenesis and longitudinal bone growth directly at the growth plate, even when the local effects of IGF-1 and IGF-2 are prevented. Further studies are warranted to elucidate the intracellular molecular mechanisms mediating the IGF-independent, growth-promoting GH effects.

Three novel IGF1R mutations in microcephalic patients with prenatal and postnatal growth impairment

BACKGROUND

IGF1R gene mutations have been associated with varying degrees of intrauterine and postnatal growth retardation, and microcephaly.

OBJECTIVE

To identify and characterize IGF1R gene variations in a cohort of 28 Argentinean children suspected of having IGF-1 insensitivity, who were selected on the basis of the association of pre/postnatal growth failure and microcephaly.

METHODS

The coding sequence and flanking intronic regions of IGF1R gene were amplified and directly sequenced. Functional characterization was performed by two in vitro assays: 1) [Methyl-(3) H] thymidine incorporation into DNA in fibroblast cell primary cultures from patients and controls treated with IGF-1 for 16-24 h. 2) PI3K/Akt pathway was evaluated with phospho-Akt (Ser473) STAR ELISA Kit (Millipore) in fibroblast cultures from patients and controls stimulated with IGF-1 for 10 min. Prepubertal clinical and GH-IGF-1 axis evaluation was followed up.

RESULTS

We identified three novel heterozygous missense mutations in three unrelated patients, de novo p.Arg1256Ser, de novo p.Asn359Tyr and p.Tyr865Cys. In control cells, proliferation assay showed that IGF-1 significantly induced DNA synthesis at 20 h and Akt phosphorylation assay that it significantly stimulated phosphorylation after 10 min (P < 0·05 by anova and Bonferroni Tests). However, no significant increase was observed in any of the three patient fibroblasts in both functional studies. GH therapy growth response in two patients was inconsistent.

CONCLUSION

These variations led to failure of the IGF1R function causing pre- and postnatal growth retardation and microcephaly. Microcephaly should be considered in the evaluation of SGA patients, because it seems to favour the frequency of detection of IGF1R mutations.

A novel GHR intronic variant, c.266+83G>T , activates a cryptic 5' splice site causing severe GHR deficiency and classical GH insensitivity syndrome

BACKGROUND/AIMS

Mutations in the human growth hormone receptor gene (GHR) are the most common cause of growth hormone insensitivity (GHI) syndrome and insulin-like growth factor (IGF-1) deficiency. The extracellular domain of GHR (encoded by exons 2-7 of the GHR gene) can be proteolytically cleaved to circulate as GH-binding protein (GHBP).

METHODS

We evaluated the cause of classical GHI (Laron) phenotypes in 3 siblings.

RESULTS

Two brothers (aged 16.5 and 14.9 years) and their half-brother (aged 11.3 years) presented with extreme short stature (height standard deviation score, SDS, of -7.05, -6.34 and -8.02, respectively). The parents were consanguineous and of normal stature. Serum GHBP levels of probands were undetectable and circulating IGF-1 and IGF-binding protein-3 were abnormally low, but GH concentrations were elevated. Molecular analysis of the GHR gene revealed homozygous deletion of exon 3, a common polymorphism, and a novel c.266+83G>T variant within intron 4 which generated a 5' donor splice site. Splicing events from this cryptic 5' donor site resulted in retention of 81 intronic nucleotides in the GHR mRNA. Long-term rhIGF-1 therapy combined with leuprolide depot increased height by +2 to +3 SDS.

CONCLUSION

The c.266+83G>T is the second intronic GHR mutation identified that activates a cryptic 5' donor splice site. The abnormal splicing event led to early protein termination and undetectable serum GHBP concentrations. © 2013 S. Karger AG, Basel.

Alu-mediated recombination defect in IGF1R: haploinsufficiency in a patient with short stature

BACKGROUND

The insulin-like growth factor (IGF) receptor (IGF1R) is essential for normal development and growth. IGF1R mutations cause IGF-1 resistance resulting in intrauterine and postnatal growth failure. The phenotypic spectrum related to IGF1R mutations remains to be fully understood.

METHODS

Auxological and endocrinological data of a patient identified previously were assessed. The patient's fibroblasts were studied to characterize the IGF1R deletion, mRNA fate, protein expression and signalling capabilities.

RESULTS

The boy, who carries a heterozygous IGF1R exon 6 deletion caused by Alu element-mediated recombination and a heterozygous SHOX variant (p.Met240Ile), was born appropriate for gestational age but developed proportionate short stature postnatally. IGF-1 levels were low-normal. None of the stigmata associated with SHOX deficiency or sporadically observed in IGF1R mutation carriers were present. Nonsense-mediated mRNA decay led to a substantial decline of IGF1R dosage and IGF-1-dependent receptor autophosphorylation but not impaired downstream signalling.

CONCLUSION

We present the first detailed report of an intragenic IGF1R deletion identified in a patient who, apart from short stature, deviates from all established markers that qualify a growth-retarded child for IGF1R analysis. Although such children will usually escape routine clinical mutation screenings, they can contribute to the understanding of factors and mechanisms that cooperate with the IGF1R.

Hypomorphism in human NSMCE2 linked to primordial dwarfism and insulin resistance

Structural maintenance of chromosomes (SMC) complexes are essential for maintaining chromatin structure and regulating gene expression. Two the three known SMC complexes, cohesin and condensin, are important for sister chromatid cohesion and condensation, respectively; however, the function of the third complex, SMC5-6, which includes the E3 SUMO-ligase NSMCE2 (also widely known as MMS21) is less clear. Here, we characterized 2 patients with primordial dwarfism, extreme insulin resistance, and gonadal failure and identified compound heterozygous frameshift mutations in NSMCE2. Both mutations reduced NSMCE2 expression in patient cells. Primary cells from one patient showed increased micronucleus and nucleoplasmic bridge formation, delayed recovery of DNA synthesis, and reduced formation of foci containing Bloom syndrome helicase (BLM) after hydroxyurea-induced replication fork stalling. These nuclear abnormalities in patient dermal fibroblast were restored by expression of WT NSMCE2, but not a mutant form lacking SUMO-ligase activity. Furthermore, in zebrafish, knockdown of the NSMCE2 ortholog produced dwarfism, which was ameliorated by reexpression of WT, but not SUMO-ligase-deficient NSMCE. Collectively, these findings support a role for NSMCE2 in recovery from DNA damage and raise the possibility that loss of its function produces dwarfism through reduced tolerance of replicative stress.

Recent research on the growth plate: Recent insights into the regulation of the growth plate

For most bones, elongation is driven primarily by chondrogenesis at the growth plates. This process results from chondrocyte proliferation, hypertrophy, and extracellular matrix secretion, and it is carefully orchestrated by complex networks of local paracrine factors and modulated by endocrine factors. We review here recent advances in the understanding of growth plate physiology. These advances include new approaches to study expression patterns of large numbers of genes in the growth plate, using microdissection followed by microarray. This approach has been combined with genome-wide association studies to provide insights into the regulation of the human growth plate. We also review recent studies elucidating the roles of bone morphogenetic proteins, fibroblast growth factors, C-type natriuretic peptide, and suppressor of cytokine signaling in the local regulation of growth plate chondrogenesis and longitudinal bone growth.

The common marmoset genome provides insight into primate biology and evolution

A first analysis of the genome sequence of the common marmoset (Callithrix jacchus), assembled using traditional Sanger methods and Ensembl annotation, has permitted genomic comparison with apes and that old world monkeys and the identification of specific molecular features a rapid reproductive capacity partly due to may contribute to the unique biology of diminutive The common marmoset has prevalence of this dizygotic primate. twins. Remarkably, these twins share placental circulation and exchange hematopoietic stem cells in utero, resulting in adults that are hematopoietic chimeras.

We observed positive selection or non-synonymous substitutions for genes encoding growth hormone / insulin-like growth factor (growth pathways), respiratory complex I (metabolic pathways), immunobiology, and proteases (reproductive and immunity pathways). In addition, both protein-coding and microRNA genes related to reproduction exhibit rapid sequence evolution. This New World monkey genome sequence enables significantly increased power for comparative analyses among available primate genomes and facilitates biomedical research application.

Large-scale pooled next-generation sequencing of 1077 genes to identify genetic causes of short stature

CONTEXT

The majority of patients presenting with short stature do not receive a definitive diagnosis. Advances in genetic sequencing allow for large-scale screening of candidate genes, potentially leading to genetic diagnoses.

OBJECTIVES

The purpose of this study was to discover genetic variants that contribute to short stature in a cohort of children with no known genetic etiology.

DESIGN

This was a prospective cohort study of subjects with short stature.

SETTING

The setting was a pediatric endocrinology and genetics clinics at an academic center.

PATIENTS

A total of 192 children with short stature with no defined genetic etiology and 192 individuals of normal stature from the Framingham Heart Study were studied.

INTERVENTION

Pooled targeted sequencing using next-generation DNA sequencing technology of the exons of 1077 candidate genes was performed.

MAIN OUTCOME MEASURES

The numbers of rare nonsynonymous genetic variants found in case patients but not in control subjects, known pathogenic variants in case patients, and potentially pathogenic variants in IGF1R were determined.

RESULTS

We identified 4928 genetic variants in 1077 genes that were present in case patients but not in control subjects. Of those, 1349 variants were novel (898 nonsynonymous). False-positive rates from pooled sequencing were 4% to 5%, and the false-negative rate was 0.1% in regions covered well by sequencing. We identified 3 individuals with known pathogenic variants in PTPN11 causing undiagnosed Noonan syndrome. There were 9 rare potentially nonsynonymous variants in IGF1R, one of which is a novel, probably pathogenic, frameshift mutation. A previously reported pathogenic variant in IGF1R was present in a control subject.

CONCLUSIONS

Large-scale sequencing efforts have the potential to rapidly identify genetic etiologies of short stature, but data interpretation is complex. Noonan syndrome may be an underdiagnosed cause of short stature.

Analysis of the insulin-like growth factor 1 receptor gene in children born small for gestational age: in vitro characterization of a novel mutation (p.Arg511Trp)

BACKGROUND

Insulin-like growth factor 1 insensitivity caused by IGF1R mutations has been previously identified as one of the causes of growth impairment in children born small for gestational age (SGA).

OBJECTIVE

To analyse the IGF1R in children born SGA.

SUBJECTS

From an initial cohort of 54 sequential children born SGA, without catch-up growth, 25 children were selected for this IGF1R study due to the presence of serum IGF-1 values above the mean for their age and sex.

METHODS

The proximal IGF1R promoter region, the entire coding region and the exon-intron boundaries were directly sequenced, and multiplex ligation-dependent probe amplification analysis was performed. Fibroblast cultures were developed from one patient with a mutation for the in vitro characterization of IGF-1 insensitivity.

RESULTS

The copy number variation analysis did not identify deletions involving the IGF1R gene. We identified two children carrying heterozygous nucleotide substitutions in IGF1R: c.16G>A/p.Gly6Arg and c.1531C>T/p.Arg511Trp. The first variant (p.Gly6Arg) was identified in control subjects (0·3%) and in a relative with normal growth; thus, it was considered to be a rare benign allelic variation. The second variant (p.Arg511Trp) was not found in 306 alleles from control subjects, and it segregated with the growth impairment phenotype in the patient's family. Fibroblasts obtained from this patient had a significantly reduced proliferative response and AKT phosphorylation after IGF-1 stimulation compared with control fibroblasts.

CONCLUSION

The identification of an inactivating IGF1R mutation in the present cohort should encourage further studies of larger series to establish the precise frequency of this molecular defect in children with growth impairment of a prenatal onset.

Familial short stature and intrauterine growth retardation associated with a novel mutation in the IGF-I receptor (IGF1R) gene

CONTEXT

IGF-I is essential for normal human growth and mediates its effects through the IGF1R. IGF1R mutations have been associated with varying degrees of intrauterine and postnatal growth retardation.

OBJECTIVE

To identify IGF1R gene mutations in a short-statured family with intrauterine growth retardation and microcephaly.

METHODS

Direct DNA sequencing was used to identify IGF1R mutations. Multiplex ligation-dependent probe amplification analyses were performed for deletions and duplications of all IGF1R exons. Functional studies were conducted to assess mutation pathogenicity.

RESULTS

A novel heterozygous IGF1R missense mutation in exon 7 (c.A1549T, p.Y487F) was identified in a short-statured girl with severe prenatal growth retardation and microcephaly. The same mutation was also identified in her mother, who presented prenatal and postnatal growth failure, and her short-statured maternal grandmother, both of whom exhibited microcephaly. The index case showed a partial response to rhGH. Functional studies performed in dermal fibroblasts from the index case and her mother showed normal IGF-I binding; however, IGF-I activation of intracellular signalling measured as AKT and extracellular signal-regulated kinase phosphorylation was markedly reduced, with patients' values being lower than those of her mother. IGF-I stimulation of DNA synthesis was significantly reduced compared with controls.

CONCLUSION

Our results show a novel missense mutation in the IGF1R gene (c.A1549T, p.Y487F) associated with prenatal and postnatal growth failure and microcephaly in the context of familial short stature. The functional studies are in line with the inactivation of one copy of the IGF1R gene with variable expression within the same family.

Homozygous mutation of the IGF1 receptor gene in a patient with severe pre- and postnatal growth failure and congenital malformations

BACKGROUND

Heterozygous mutations in the IGF1 receptor (IGF1R) gene lead to partial resistance to IGF1 and contribute to intrauterine growth retardation (IUGR) with postnatal growth failure. To date, homozygous mutations of this receptor have not been described.

SUBJECT

A 13.5-year-old girl born from healthy first-cousin parents presented with severe IUGR and persistent short stature. Mild intellectual impairment, dysmorphic features, acanthosis nigricans, and cardiac malformations were also present.

METHODS

Auxological and endocrinological profiles were measured. All coding regions of the IGF1R gene including intron boundaries were amplified and directly sequenced. Functional characterization was performed by immunoblotting using patient's fibroblasts.

RESULTS

IGF1 level was elevated at 950NG/ML (+7 S.D.). Fasting glucose level was normal associated with high insulin levels at baseline and during an oral glucose tolerance test. Fasting triglyceride levels were elevated. sequencing of the IGF1R gene led to the identification of a homozygous variation in exon 2: c.119G>T (p.Arg10Leu). As a consequence, IGF1-dependent receptor autophosphorylation and downstream signaling were reduced in patient's fibroblasts. Both parents were heterozygous for the mutation.

CONCLUSION

The homozygous mutation of the IGF1R is associated with severe IUGR, dysmorphic features, and insulin resistance, while both parents were asymptomatic heterozygous carriers of the same mutation.

IGF receptor gene variants in normal adolescents: effect on stature

OBJECTIVE

IGF1 is essential for human growth and mediates its effects through the type 1 IGF receptor (IGF1R). Our objective was to determine the frequency of certain previously reported IGF1R gene variants in the normal population and their effect on stature.

DESIGN

A cross-sectional study was conducted in a population of 2500 children enrolled in public school grades 5 through 12 for whom DNA and anthropometric data were available. Subjects were genotyped at five previously reported loci that affect receptor abundance or function.

METHODS

The frequency of the following IGF1R variants Arg108Gln, Lys115Asn, Arg59stop, Arg481Gln, and Arg605His was measured by a PCR-based assay. Circulating concentrations of IGF1 or IGF binding protein-3 (IGFBP3) were measured by ELISA in those affected and matched controls.

RESULTS

A scan of 1300 subjects detected none with Arg108Gln, Lys115Asn, or Arg59stop mutations. In contrast, nucleotide changes leading to heterozygosity at codon 605 were identified in nine of 2500 subjects and six of 1800 subjects at codon 481. These individuals were, on average, 4 cm shorter than the others. There were no differences in circulating concentrations of IGF1 or IGFBP3 between those with the gene variants and controls matched for sex, ethnicity, age, and BMI.

CONCLUSION

Rare IGF1R variants exerting a moderate effect on stature are present in the general population, supporting the importance of IGF1R function in growth control and indicating that variation in height within healthy individuals may be explained, in some cases, by larger effects of a small subset of gene variants.

Clinical and functional characterization of a patient carrying a compound heterozygous pericentrin mutation and a heterozygous IGF1 receptor mutation

Intrauterine and postnatal longitudinal growth is controlled by a strong genetic component that regulates a complex network of endocrine factors integrating them with cellular proliferation, differentiation and apoptotic processes in target tissues, particularly the growth centers of the long bones. Here we report on a patient born small for gestational age (SGA) with severe, proportionate postnatal growth retardation, discreet signs of skeletal dysplasia, microcephaly and moyamoya disease. Initial genetic evaluation revealed a novel heterozygous IGF1R p.Leu1361Arg mutation affecting a highly conserved residue with the insulin-like growth factor type 1 receptor suggestive for a disturbance within the somatotropic axis. However, because the mutation did not co-segregate with the phenotype and functional characterization did not reveal an obvious impairment of the ligand depending major IGF1R signaling capabilities a second-site mutation was assumed. Mutational screening of components of the somatotropic axis, constituents of the IGF signaling system and factors involved in cellular proliferation, which are described or suggested to provoke syndromic dwarfism phenotypes, was performed. Two compound heterozygous PCNT mutations (p.[Arg585X];[Glu1774X]) were identified leading to the specification of the diagnosis to MOPD II. These investigations underline the need for careful assessment of all available information to derive a firm diagnosis from a sequence aberration.