IGFALS gene dosage effects on serum IGF-I and glucose metabolism, body composition, bone growth in length and width, and the pharmacokinetics of recombinant human IGF-I administration

Endocrine and cellular physiology and pathology of the insulin-like growth factor acid-labile subunit

The acid-labile subunit (ALS) of the insulin-like growth factor (IGF) binding protein (IGFBP) complex, encoded in humans by IGFALS, has a vital role in regulating the endocrine transport and bioavailability of IGF-1 and IGF-2. Accordingly, ALS has a considerable influence on postnatal growth and metabolism. ALS is a leucine-rich glycoprotein that forms high-affinity ternary complexes with IGFBP-3 or IGFBP-5 when they are occupied by either IGF-1 or IGF-2. These complexes constitute a stable reservoir of circulating IGFs, blocking the potentially hypoglycaemic activity of unbound IGFs. ALS is primarily synthesized by hepatocytes and its expression is lower in non-hepatic tissues. ALS synthesis is strongly induced by growth hormone and suppressed by IL-1β, thus potentially serving as a marker of growth hormone secretion and/or activity and of inflammation. IGFALS mutations in humans and Igfals deletion in mice cause modest growth retardation and pubertal delay, accompanied by decreased osteogenesis and enhanced adipogenesis. In hepatocellular carcinoma, IGFALS is described as a tumour suppressor; however, its contribution to other cancers is not well delineated. This Review addresses the endocrine physiology and pathology of ALS, discusses the latest cell and proteomic studies that suggest emerging cellular roles for ALS and outlines its involvement in other disease states.

A blood-based multi-omic landscape for the molecular characterization of kidney stone disease

Kidney stone disease (KSD, also named renal calculi, nephrolithiasis, or urolithiasis) is a common urological disease entailing the formation of minerals and salts that form inside the urinary tract, frequently caused by diabetes, high blood pressure, hypertension, and monogenetic components in most patients. 10% of adults worldwide are affected by KSD, which continues to be highly prevalent and with increasing incidence. For the identification of novel therapeutic targets in KSD, we adopted high-throughput sequencing and mass spectrometry (MS) techniques in this study and carried out an integrative analysis of exosome proteomic data and DNA methylation data from blood samples of normal and KSD individuals. Our research delineated the profiling of exosomal proteins and DNA methylation in both healthy individuals and those afflicted with KSD, finding that the overexpressed proteins and the demethylated genes in KSD samples are associated with immune responses. The consistency of the results in proteomics and epigenetics supports the feasibility of the comprehensive strategy. Our insights into the molecular landscape of KSD pave the way for a deeper understanding of its pathogenic mechanism, providing an opportunity for more precise diagnosis and targeted treatment strategies for KSD.

Genome-Wide Detection for Runs of Homozygosity in Baoshan Pigs Using Whole Genome Resequencing

Baoshan pigs (BS) are a local breed in Yunnan Province that may face inbreeding owing to its limited population size. To accurately evaluate the inbreeding level of the BS pig population, we used whole-genome resequencing to identify runs of homozygosity (ROH) regions in BS pigs, calculated the inbreeding coefficient based on pedigree and ROH, and screened candidate genes with important economic traits from ROH islands. A total of 22,633,391 SNPS were obtained from the whole genome of BS pigs, and 201 ROHs were detected from 532,450 SNPS after quality control. The number of medium-length ROH (1-5 Mb) was the highest (98.43%), the number of long ROH (>5 Mb) was the lowest (1.57%), and the inbreeding of BS pigs mainly occurred in distant generations. The inbreeding coefficient FROH, calculated based on ROH, was 0.018 ± 0.016, and the FPED, calculated based on the pedigree, was 0.027 ± 0.028, which were positively correlated. Forty ROH islands were identified, containing 507 genes and 891 QTLs. Several genes were associated with growth and development (IGFALS, PTN, DLX5, DKK1, WNT2), meat quality traits (MC3R, ACSM3, ECI1, CD36, ROCK1, CACNA2D1), and reproductive traits (NPW, TSHR, BMP7). This study provides a reference for the protection and utilization of BS pigs.

Novel IGFALS mutations with predicted pathogenetic effects by the analysis of AlphaFold structure

PURPOSE

According to the American College of Medical Genetics (ACMG) classification, variants of uncertain significance (VUS) are gene variations whose impact on the disease risk is not yet known. VUS, therefore, represent an unmet need for genetic counselling. Aim of the study is the use the AlphaFold artificial intelligence algorithm to predict the impact of novel mutations of the IGFALS gene, detected in a subject with short stature and initially classified as VUS according to the ACMG classification.

METHODS

A short-stature girl and her parents have been investigated. IGFALS mutations have been detected through clinical exome and confirmed by Sanger sequencing. The potential presence of co-occurring gene alterations was investigated in the proband by whole exome and CGH array. Structure of the ALS protein (encoded by the IGFALS gene) was evaluated through the AlphaFold artificial intelligence algorithm.

RESULTS

Two IGFALS variants were found in the proband: c.1349T > C (p.Leu450Pro) and c.1363_1365delCTC (p.Leu455del), both classified as VUS, according to ACMG. Parents' analysis highlighted the in trans position of the two variants. AlphaFold showed that the mutated positions were found the concave side a horseshoe structure of the ALS protein, likely interfering with protein-protein interactions. According to a loss of function (LoF) effect of the two variants, reduced levels of the IGF1 and IGFBP-3 proteins, as well as a growth hormone (GH) excess were detected in the proband's serum.

CONCLUSIONS

By using the AlphaFold structure we were able to predict two IGFALS gene mutations initially classified as VUS, as potentially pathogenetic. Our proof-of-concept showed a potential application of AlphaFold as tool to a better inform VUS interpretation of genetic tests.

UPLC-HDMSE to discover serum biomarkers in adults with type 1 diabetes

Type 1 diabetes (T1D) is a complex disease with metabolic and functional changes that can alter an individual's proteome. An LC-MS/MS analytical method, in an HDMS^E system, was used to identify differentially expressed proteins in the high abundance protein-depleted serum of T1D patients and healthy controls. Samples were processed in Progenesis QI for Proteomics software. A functional enrichment of the proteins was performed with Gene Ontology and ToppGene, and the interactions were visualized by STRING 11.5. As a result, 139 proteins were identified, 14 of which were downregulated in the serum of patients with T1D compared to controls. Most of the differentially expressed proteins were shown to be involved with the immune system, inflammation, and growth hormone stimulus response, and were associated with the progression of T1D. Differential protein expression data showed for the first-time changes in CPN2 expression levels in the serum of patients with T1D. Our findings indicate that these proteins are targets of interest for future investigations and for validation of protein biomarkers in T1D.

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.

Identifying Thyroid Carcinoma-Related Genes by Integrating GWAS and eQTL Data

Thyroid carcinoma (TC) is the most common endocrine malignancy. The incidence rate of thyroid cancer has increased rapidly in recent years. The occurrence and development of thyroid cancers are highly related to the massive genetic and epigenetic changes. Therefore, it is essential to explore the mechanism of thyroid cancer pathogenesis. Genome-Wide Association Studies (GWAS) have been widely used in various diseases. Researchers have found multiple single nucleotide polymorphisms (SNPs) are significantly related to TC. However, the biological mechanism of these SNPs is still unknown. In this paper, we used one GWAS dataset and two eQTL datasets, and integrated GWAS with expression quantitative trait loci (eQTL) in both thyroid and blood to explore the mechanism of mutations and causal genes of thyroid cancer. Finally, we found rs1912998 regulates the expression of IGFALS (P = 1.70E-06) and HAGH (P = 5.08E-07) in thyroid, which is significantly related to thyroid cancer. In addition, KEGG shows that these genes participate in multiple thyroid cancer-related pathways.

The role of acid-labile subunit (ALS) in the modulation of GH-IGF-I action

Acid-labile subunit (ALS) deficiency (ACLSD) constitutes the first monogenic defect involving a member of the Insulin-like Growth Factor (IGF) binding protein system. The lack of ALS completely disrupts the circulating IGF system. Autocrine/paracrine action of local produced IGF-I could explain the mild effect on growth. In the present work we have revised the more relevant clinical and biochemical consequences of complete ACLSD in 61 reported subjects from 31 families. Low birth weight and/or length, reduced head circumference, height between -2 and -3 SD, pubertal delay and insulin resistance are commonly observed. Partial ACLSD could be present in children initially labeled as idiopathic short stature, presenting low IGF-I levels, suggesting that one functional IGFALS allele is insufficient to stabilize ternary complexes. Dysfunction of the GH-IGF axis observed in ACLSD may eventually result in increased risk for type-2 diabetes and tumor progression. Consequently, long term surveillance is recommended in these patients.

Therapy with recombinant human IGF-1 for children with primary insulin-like growth factor-I deficiency

The efficacy and safety of IGF-1 therapy in patients with severe primary IGF-I deficiency has been evaluated for more than two decades. Most of the therapeutic experience comes from treating the more severe IGF-I deficient patients, who usually present with a phenotype characteristic of growth hormone receptor deficiency or Laron syndrome. Although most of these patients do not experience enough catchup growth to bring their height into normal range, many individuals achieve an adult height significantly greater than what would have been predicted in the absence of IGF-1 therapy. In the last couple of years a few reports on the benefit of IGF-1 therapy for patients with milder types of IGF-I deficiency have also been published, with variable height outcomes. More short children with prior diagnosis of idiopathic short stature are now being diagnosed with specific molecular defects of the growth hormone/IGF-I axis. Because of this, the clinical spectrum of primary IGF-I deficiency is widening to include many patients with such a milder phenotype, creating a need for well-designed long-term clinical studies evaluating the growth response to growth promoting agents such as rhIGF-1 in these individuals.

A Novel Homozygous Mutation of the Acid-Labile Subunit (IGFALS) Gene in a Male Adolescent

Acid-labile subunit (ALS) forms ternary complexes with insulin like growth factor-1 (IGF-1) and IGF-binding protein-3 (IGFBP-3) and is essential for normal circulating IGF-1 levels. The IGFALS gene encodes the ALS and mutations in IGFALS cause ALS deficiency. We describe a patient with ALS deficiency with a novel homozygous frameshift mutation in IGFALS presenting with short stature and delayed puberty but ultimately achieving an adult height (AH) comparable to his target height (TH). A 15.25 year old boy presented with short stature (149.9 cm, -3.04 standard deviation score). The patient had a low circulating IGF-1 concentration, extremely low IGFBP-3 concentration, insulin resistance and osteopenia. The peak growth hormone (GH) response to GH stimulation test was high (31.6 ng/mL). Sequencing of IGFALS revealed a novel, homozygous, frameshift mutation (p.Ser555Thrfs.19). His mother and elder sister were heterozygous carriers. Although he had delayed puberty and short stature at the onset of puberty, he reached his TH and an AH similar to those of his heterozygous mother and sister. The heterozygous carriers had normal or low IGF-1 concentrations and low IGFBP-3 concentrations but not as markedly low as that of the patient. They had normally timed puberty, insulin metabolism and bone mineral density (BMD). The phenotype of ALS deficiency is quite variable. Despite short stature and delayed puberty, patients can achieve normal pubertal growth and AH. ALS deficiency may cause osteopenia and hyperinsulinemia. Heterozygous carriers may have normal prenatal growth, puberty, insulin metabolism and BMD.

Comparative transcriptomic analysis of hypothalamus-pituitary-liver axis in bighead carp (Hypophthalmichthys nobilis) with differential growth rate

Background

Growth rate is one of the most important features for aquaculture species and deciphering its regulation mechanism has great significance both in genetics and in economics. Hypothalamus-pituitary growth axis (HP growth axis) or neuro-endocrine axis plays a vital role in growth regulation in different aquaculture animals.

Results

In this study, the HP and liver transcriptomes of two female groups (H and L) with phenotypically extreme growth rate were sequenced using RNA-Seq. A total of 30,524 and 22,341 genes were found expressed in the two tissues, respectively. The average expression levels for the two tissues were almost the same, but the median differed significantly. A differential expression analysis between H and L groups identified 173 and 204 differentially expressed genes (DEGs) in HP and liver tissue, respectively. Pathway analysis revealed that DEGs in HP tissue were enriched in regulation of cell proliferation and angiogenesis while in liver tissue these genes were overrepresented in sterol biosynthesis and transportation. Genomic overlapping analyses found that 4 and 5 DEGs were within growth-related QTL in HP and liver tissue respectively. A deeper analysis of these 9 genes revealed 3 genes were functionally linked to the trait of interest. The expression of 2075 lncRNAs in HP tissue and 1490 in liver tissue were also detected, and some of lncRNAs were highly expressed in the two tissues.

Conclusions

Above all, the results of the present study greatly contributed to the knowledge of the regulation of growth and then assisted the design of new selection strategies for bighead carp with improved growth-related traits.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5691-4) contains supplementary material, which is available to authorized users.

Nonclassical GH Insensitivity: Characterization of Mild Abnormalities of GH Action

GH insensitivity (GHI) presents in childhood with growth failure and in its severe form is associated with extreme short stature and dysmorphic and metabolic abnormalities. In recent years, the clinical, biochemical, and genetic characteristics of GHI and other overlapping short stature syndromes have rapidly expanded. This can be attributed to advancing genetic techniques and a greater awareness of this group of disorders. We review this important spectrum of defects, which present with phenotypes at the milder end of the GHI continuum. We discuss their clinical, biochemical, and genetic characteristics. The objective of this review is to clarify the definition, identification, and investigation of this clinically relevant group of growth defects. We also review the therapeutic challenges of mild GHI.

Sequential measurements of IGF-I serum concentrations in adolescents with Laron syndrome treated with recombinant human IGF-I (rhIGF-I)

Background Recombinant human insulin-like growth factor 1 (rhIGF-I) has been approved as an orphan drug for the treatment of growth failure in children and adolescents with severe primary IGF-I deficiency (SPIGFD) with little pharmacokinetic data available. Therefore, sequential measurements of serum IGF-I, glucose, potassium, insulin and cortisol were performed in patients treated with rhIGF-I to evaluate their significance in safety and efficacy. Methods Repetitive blood samples were taken after meals before and 30, 60, 120, 180 and 360 min after rhIGF-I injections in two male patients with Laron syndrome at times of dose adjustments. Results Maximal IGF-I concentrations were observed 2 h after injections (495 ng/mL) and concentrations were still higher 6 h after injections than at baseline (303 ng/mL vs. 137 ng/mL). Thirteen percent of all and 33% of maximum IGF-I concentrations were greater than +2 standard deviation score (SDS) calculated for bone age (BA) (IGF-I SDS BA) rather than chronological age (CA) as BA was significantly delayed to CA by 3.2 years (p=0.0007). Height velocities correlated with individual maximum IGF-I SDS BA (ρ=0.735; p<0.0001). Serum insulin, cortisol and glucose did not correlate with IGF-I concentrations, but serum potassium showed a negative correlation (ρ=-0.364; p<0.0001) with IGF-I concentrations. Conclusions Sequential measurements of serum IGF-I, glucose and potassium in patients with Laron syndrome may aid in optimizing and individualizing rhIGF-I treatment. IGF-I concentrations should be referenced according to BA which better reflects the biological age. The inverse correlation of IGF-I and serum potassium concentrations after injections of rhIGF-I has not been reported before and warrants further consideration.

New Genetic Diagnoses of Short Stature Provide Insights into Local Regulation of Childhood Growth

Idiopathic short stature is a common condition with a heterogeneous etiology. Advances in genetic methods, including genome sequencing techniques and bioinformatics approaches, have emerged as important tools to identify the genetic defects in families with monogenic short stature. These findings have contributed to the understanding of growth regulation and indicate that growth plate chondrogenesis, and therefore linear growth, is governed by a large number of genes important for different signaling pathways and cellular functions, including genetic defects in hormonal regulation, paracrine signaling, cartilage matrix, and fundamental cellular processes. In addition, mutations in the same gene can cause a wide phenotypic spectrum depending on the severity and mode of inheritance of the mutation.
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Pharmacokinetics of IGF-1 in PAPP-A2-Deficient Patients, Growth Response, and Effects on Glucose and Bone Density

CONTEXT

The pregnancy-associated plasma protein A2 (PAPP-A2) cleaves insulinlike growth factor binding proteins 3 and 5, releasing free insulinlike growth factor 1 (IGF-1). Homozygous mutations in PAPP-A2 result in growth failure with elevated total but low free IGF-1.

OBJECTIVE

To determine the 24-hour pharmacokinetic (PK) profile of free and total IGF-1 after a dose of recombinant human insulinlike growth factor 1 (rhIGF-1). We describe the growth response and effects on glucose metabolism and bone mineral density (BMD) after 1 year of rhIGF-1 therapy.

DESIGN AND PATIENTS

Three affected siblings, their heterozygous parents, and two healthy controls participated. The subjects received a dose of rhIGF-1, followed by serial blood samples collected over 24 hours. The two younger siblings were started on rhIGF-1 treatment. An oral glucose tolerance test and dual-energy X-ray absorptiometry scans were obtained at baseline and after 1 year of treatment.

RESULTS

Subcutaneous administration of rhIGF-1 increased the concentration of free and total IGF-1 in patients with PAPP-A2 deficiency. The PK profile was comparable in all participants. At baseline, all three subjects demonstrated insulin resistance and below-average BMD. Treatment with rhIGF-1 is ongoing in the youngest patient but was discontinued in his brother because of the development of pseudotumor cerebri. The treated patient had an increase in height velocity from 3.0 to 6.2 cm/y, resolution of insulin resistance, and an increase in total body BMD.

CONCLUSIONS

rhIGF-1 at standard dosages resulted in similar PK characteristics in patients with PAPP-A2 deficiency, heterozygous relatives, and healthy controls. The youngest affected patient experienced a modest growth response to therapy with rhIGF-1, as well as beneficial effects on glucose metabolism and bone mass.

Characterization of four Latin American families confirms previous findings and reveals novel features of acid-labile subunit deficiency

OBJECTIVE

Acid-labile subunit deficiency (ACLSD), caused by inactivating mutations in both IGFALS gene alleles, is characterized by marked reduction in IGF-I and IGFBP-3 levels associated with mild growth retardation. The aim of this study was to expand the known phenotype and genetic characteristics of ACLSD by reporting data from four index cases and their families.

DESIGN

Auxological data, biochemical and genetic studies were performed in four children diagnosed with ACLSD and all available relatives.

METHODS

Serum levels of IGF-I, IGFBP-3, acid-labile subunit (ALS), and in vitro ternary complex formation (ivTCF) were determined. After sequencing the IGFALS gene, pathogenicity of novel identified variants was evaluated by in vitro expression in transfected Chinese hamster ovarian (CHO) cells. ALS protein was detected in patients' sera and CHO cells conditioned media and lysates by Western immunoblot (WIB).

RESULTS

Four index cases and four relatives were diagnosed with ACLSD. The following variants were found: p.Glu35Glyfs*17, p.Glu35Lysfs*87, p.Leu213Phe, p.Asn276Ser, p.Leu409Phe, p.Ala475Val and p.Ser490Trp. ACLSD patients presented low IGF-I and low or undetectable levels of IGFBP-3 and ALS. Seven out of 8 patients did not form ivTCF.

CONCLUSIONS

This study confirms previous findings in ACLSD, such as the low IGF-I and a more severe reduction in IGFBP-3 levels, and a gene dosage effect observed in heterozygous carriers (HC). In addition, father-to-son transmission (father compound heterozygous and mother HC), preservation of male fertility, and marginal ALS expression with potential involvement in preserved responsiveness to rhGH treatment, are all novel aspects, not previously reported in this condition.

Genetics of Short Stature

Short stature is a common and heterogeneous condition that is often genetic in etiology. For most children with genetic short stature, the specific molecular causes remain unknown; but with advances in exome/genome sequencing and bioinformatics approaches, new genetic causes of growth disorders have been identified, contributing to the understanding of the underlying molecular mechanisms of longitudinal bone growth and growth failure. Identifying new genetic causes of growth disorders has the potential to improve diagnosis, prognostic accuracy, and individualized management, and help avoid unnecessary testing for endocrine and other disorders.

Clinical and biochemical characteristics and bone mineral density of homozygous, compound heterozygous and heterozygous carriers of three novel IGFALS mutations

OBJECTIVE

Acid-labile subunit (ALS) deficiency (ACLSD), caused by homozygous or compound heterozygous IGFALS mutations, is associated with moderate short stature, delayed puberty, low serum IGF-I and ALS and extremely low serum IGFBP-3. Its effect on birth weight, head circumference, bone mineral density (BMD), serum IGF-II and IGFBP-2 is uncertain, as well as the phenotype of heterozygous carriers of IGFALS mutations (partial ACLSD).

DESIGN

From all available members of five Turkish families, carrying three mutations in exon 2 of IGFALS (c.1462G > A, p.Asp488Asn (families A, B, E); c.251A > G, p.Asn84Ser (families C and E) and c.1477del, p.Arg493fs (family D)), clinical, laboratory and BMD data were collected.

METHODS

Auxological and biochemical findings were expressed as SDS for age and gender. Ternary complex formation in serum was investigated by size-exclusion chromatography. BMD using DXA bone densitometry was adjusted for height and age (Ha-BMD z-score).

RESULTS

In ACLSD (n = 24), mean ± s.d. height SDS (-2.7 ± 1.2), head circumference SDS (-2.3 ± 0.5) and body mass index (BMI) (-0.6 ± 1.0 SDS) were lower than those in partial ACLSD (n = 26, P ≤ 0.01) and birth weight SDS (n = 7) tended to be lower (-2.2 ± 1.1 vs -0.6 ± 0.3 in partial ACLSD (P = 0.07)). Serum IGF-I was -3.7 ± 1.4 vs -1.0 ± 1.0, IGF-II: -5.6 ± 0.7 vs -1.3 ± 0.7, ALS: <-4.4 ± 1.2 vs -2.1 ± 0.9 and IGFBP-3: -9.0 ± 1.9 vs -1.6 ± 0.8 SDS respectively (P < 0.001). Ha-BMD z-score was similar and normal in both groups.

CONCLUSIONS

To the known phenotype of ACLSD (i.e. short stature, reduced serum levels of IGF-I and ALS, extremely low serum IGFBP-3 and disturbed ternary complex formation), we add reduced birth weight, head circumference and serum IGF-II.

Treatment of Paget's Disease of Bone with Denosumab: Case Report and Literature Review

Paget's disease is a condition involving focal overactivity of bone cells (osteoblasts and osteoclasts), which can result in significant skeletal morbidity. It is unclear in which bone cells the causative lesion resides. It is managed effectively with potent bisphosphonates, but treatment is difficult if these drugs are contraindicated. We describe a 75-year-old woman with Paget's disease involving the skull who was intolerant of bisphosphonates, so was treated with denosumab. This intervention normalized serum alkaline phosphatase for 4-8 months after each injection and led to some symptomatic improvement. Scintigraphic activity in the lesion was improved but not normalized. We conclude that reduction in RANKL activity by denosumab only partially corrects pagetic activity, indicating that the osteoclast overactivity of Paget's disease is not wholly mediated by RANKL. Denosumab has some clinical utility in Paget's disease and may become a second-line agent in those with contraindications to intravenous bisphosphonates.

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.

Truncation of POC1A associated with short stature and extreme insulin resistance

We describe a female proband with primordial dwarfism, skeletal dysplasia, facial dysmorphism, extreme dyslipidaemic insulin resistance and fatty liver associated with a novel homozygous frameshift mutation in POC1A, predicted to affect two of the three protein products of the gene. POC1A encodes a protein associated with centrioles throughout the cell cycle and implicated in both mitotic spindle and primary ciliary function. Three homozygous mutations affecting all isoforms of POC1A have recently been implicated in a similar syndrome of primordial dwarfism, although no detailed metabolic phenotypes were described. Primary cells from the proband we describe exhibited increased centrosome amplification and multipolar spindle formation during mitosis, but showed normal DNA content, arguing against mitotic skipping, cleavage failure or cell fusion. Despite evidence of increased DNA damage in cells with supernumerary centrosomes, no aneuploidy was detected. Extensive centrosome clustering both at mitotic spindles and in primary cilia mitigated the consequences of centrosome amplification, and primary ciliary formation was normal. Although further metabolic studies of patients with POC1A mutations are warranted, we suggest that POC1A may be added to ALMS1 and PCNT as examples of centrosomal or pericentriolar proteins whose dysfunction leads to extreme dyslipidaemic insulin resistance. Further investigation of links between these molecular defects and adipose tissue dysfunction is likely to yield insights into mechanisms of adipose tissue maintenance and regeneration that are critical to metabolic health.

Glucose intolerance in aging male IGFBP-3 transgenic mice: differential effects of human IGFBP-3 and its mutant IGFBP-3 devoid of IGF binding ability

We have reported a reduction of insulin secretion and glucose intolerance in young mice overexpressing human IGFBP-3 (phosphoglycerate kinase [PGK]BP3) or its mutant Gly56/Gly80/Gly81-IGFBP-3 (PGKmutBP3) under the PGK promoter. Here, we investigated changes in glucose and lipid homeostasis with age in PGKBP3 and PGKmutBP3 mice compared with wild-type mice. Body weight, glucose tolerance, insulin tolerance, visceral fat, interscapular brown adipose tissue (BAT), serum lipids, and pancreas histology were examined at age 3, 6, and 12 months. Murine IGFBP-3 was similar in all mouse genotypes and decreased with age in parallel with total IGF-1. Visceral fat and BAT masses increased in PGKmutBP3 mice, but not in PGKBP3 mice. Glucose tolerance was impaired in both PGKBP3 and PGKmutBP3 mice. However, PGKBP3 mice had increased expression of uncoupling protein-1 in BAT and reduced adiposity, and continued to have smaller pancreatic β-cell mass and reduced insulin secretion through age 12 months. In contrast, PGKmutBP3 mice developed insulin resistance with age in association with pancreatic β-cell hyperplasia, impaired expression of uncoupling protein-1 in BAT, and increased adiposity. In addition, both PGKBP3 and PGKmutBP3 mice had elevated glycerol in the circulation, but only PGKBP3 mice had elevated free fatty acids and only PGKmutBP3 mice had elevated triglycerides. Estimated free IGF-1 did not increase with age in transgenic mice, as it did in wild-type mice. Thus, overexpression of human IGFBP-3 or its mutant devoid of IGF binding ability leads to glucose intolerance with, however, different effects on insulin secretion, insulin sensitivity, and lipid homeostasis in aging mice.