rhIGF-1 Treatment Increases Bone Mineral Density and Trabecular Bone Structure in Children with PAPP-A2 Deficiency

Sex-based differences in growth-related IGF1 signaling in response to PAPP-A2 deficiency: comparative effects of rhGH, rhIGF1 and rhPAPP-A2 treatments

BACKGROUND

Children with pregnancy-associated plasma protein-A2 (PAPP-A2) mutations resulting in low levels of bioactive insulin-like growth factor-1 (IGF1) and progressive postnatal growth retardation have improved growth velocity and height following recombinant human (rh)IGF1 treatment. The present study aimed to evaluate whether Pappa2 deficiency and pharmacological manipulation of GH/IGF1 system are associated with sex-specific differences in growth-related signaling pathways.

METHODS

Plasma, hypothalamus, pituitary gland and liver of Pappa2ko/ko mice of both sexes, showing reduced skeletal growth, and liver of these mice treated with rhGH, rhIGF1 and rhPAPP-A2 from postnatal day (PND) 5 to PND35 were analyzed.

RESULTS

Reduced body and femur length of Pappa2ko/ko mice was associated with increases in: (1) components of IGF1 ternary complexes (IGF1, IGFBP5/Igfbp5, Igfbp3, Igfals) in plasma, hypothalamus and/or liver; and (2) key signaling regulators (phosphorylated PI3K, AKT, mTOR, GSK3β, ERK1/2 and AMPKα) in hypothalamus, pituitary gland and/or liver, with Pappa2ko/ko females having a more prominent effect. Compared to rhGH and rhIGF1, rhPAPP-A2 specifically induced: (1) increased body and femur length, and reduced plasma total IGF1 and IGFBP5 concentrations in Pappa2ko/ko females; and (2) increased Igf1 and Igf1r levels and decreased Ghr, Igfbp3 and Igfals levels in the liver of Pappa2ko/ko females. These changes were accompanied by lower phospho-STAT5, phospho-AKT and phospho-ERK2 levels and higher phospho-AMPK levels in the liver of Pappa2ko/ko females.

CONCLUSIONS

Sex-specific differences in IGF1 system and signaling pathways are associated with Pappa2 deficiency, pointing to rhPAPP-A2 as a promising drug to alleviate postnatal growth retardation underlying low IGF1 bioavailability in a female-specific manner.

Five-Year Therapy with Recombinant Human Insulin-Like Growth Factor-1 in a Patient with PAPP-A2 Deficiency

INTRODUCTION

The metalloproteinase pregnancy-associated plasma protein A2 (PAPP-A2) cleaves insulin-like growth factor (IGF)-binding proteins 3 and 5 to release bioactive IGF-I from its ternary complex. Patients with mutations in PAPP-A2 have growth failure and low free IGF-I despite elevated total IGF-I. We describe 5-year treatment response to recombinant human IGF-1 (rhIGF-1) in a patient with PAPP-A2 deficiency, and the phenotype of PAPP-A2 deficiency in three siblings.

METHODS

Two siblings (P2, P3) with PAPP-A2 deficiency were recruited for rhIGF-1 therapy at 120 μg/kg subcutaneous twice daily, along with a third sibling (P1) for phenotyping. We evaluated efficacy and safety of rhIGF-1 therapy, including effect on metabolic measures and bone mineral density (BMD).

RESULTS

Treatment with rhIGF-1 was started in 10.4-year- (P3) and 14.5-year (P2)-old brothers. P2 discontinued therapy due to pseudotumor cerebri. P3 continued rhIGF-1 for 5 years; height velocity increased (3.0 cm/year at baseline; 5.0-7.6 cm/year thereafter) as did height SDS (+0.6). P3's pubertal onset was at 12.4 year. BMD height-adjusted Z-score modestly improved for lumbar spine (+0.4), and decreased in forearm (-0.2) and hip (-0.3). All siblings had hyperinsulinemia. Impaired glucose tolerance (IGT) resolved in P1. P2 showed worsening glucose tolerance (2-h glucose: 225 mg/dL). Impaired fasting glucose and hyperinsulinemia initially resolved for P3, but IGT (2-h glucose: 152 mg/dL) developed during puberty.

CONCLUSION

Therapy with rhIGF-1 modestly improved linear growth in one patient with PAPP-A2 deficiency, but without true catch-up. Therapy was associated with pseudotumor cerebri in a sibling. Initial improvement in BMD and glycemic pattern on rhIGF-1 was not sustained during puberty.

Pappalysins and Stanniocalcins and Their Relationship With the Peripheral IGF Axis in Newborns and During Development

CONTEXT

Pappalysins (PAPP-A, PAPP-A2) modulate body growth by increasing insulin-like growth factor I (IGF-I) bioavailability through cleavage of insulin-like growth factor binding proteins (IGFBPs) and are inhibited by stanniocalcins (STC1, STC2). Normative data on these novel factors, as well as on free IGF-I and uncleaved fractions of IGFBPs, are not well established.

OBJECTIVE

This work aimed to determine serum concentrations of PAPP-A, PAPP-A2, STC1, and STC2 in relationship with other growth hormone (GH)-IGF axis parameters during development.

METHODS

Full-term newborns (150; gestational age: 39.30 ± 1.10 weeks), 40 preterm newborns (30.87 ± 3.35 weeks), and 1071 healthy individuals (aged 1-30 years) were included in the study and divided according to their Tanner stages (males and females): I:163 males, 154 females; II:100 males, 75 females; III:83 males, 96 females; IV: 77 males, 86 females; and V:109 males,128 females.

RESULTS

Serum concentrations of PAPP-A, PAPP-A2, STC1, STC2, IGFBP-2, total IGFBP-4, and total IGFBP-5 were elevated at birth and declined throughout childhood. In postnatal life, PAPP-A2 concentrations decreased progressively in concomitance with the free/total IGF-I ratio; however, stanniocalcin concentrations remained stable. PAPP-A2 concentrations positively correlated with the free/total IGF-I ratio (r = +0.28; P < .001) and negatively with the intact/total IGFBP-3 ratio (r = -0.23; P < .001). PAPP-A concentrations inversely correlated with intact/total IGFBP-4 ratio (r = -0.21; P < .001), with PAPP-A concentrations being lower in females at all ages. Association studies indicate the importance of stanniocalcins and pappalysins in the control of this axis in an age-specific manner.

CONCLUSION

This study provides reference values of pappalysins and stanniocalcins, which modulate IGF-I activity by changing the concentrations of cleaved and uncleaved IGFBPs.

Skeletal disorders associated with the growth hormone-insulin-like growth factor 1 axis

Growth hormone (GH) and insulin-like growth factor 1 (IGF1) are important regulators of bone remodelling and metabolism and have an essential role in the achievement and maintenance of bone mass throughout life. Evidence from animal models and human diseases shows that both GH deficiency (GHD) and excess are associated with changes in bone remodelling and cause profound alterations in bone microstructure. The consequence is an increased risk of fractures in individuals with GHD or acromegaly, a condition of GH excess. In addition, functional perturbations of the GH-IGF1 axis, encountered in individuals with anorexia nervosa and during ageing, result in skeletal fragility and osteoporosis. The effect of interventions used to treat GHD and acromegaly on the skeleton is variable and dependent on the duration of the disease, the pre-existing skeletal state, coexistent hormone alterations (such as those occurring in hypogonadism) and length of therapy. This variability could also reflect the irreversibility of the skeletal structural defect occurring during alterations of the GH-IGF1 axis. Moreover, the effects of the treatment of GHD and acromegaly on locally produced IGF1 and IGF binding proteins are uncertain and in need of further study. This Review highlights the pathophysiological, clinical and therapeutic aspects of skeletal fragility associated with perturbations in the GH-IGF1 axis.

Pregnancy-Associated Plasma Protein (PAPP)-A2 in Physiology and Disease

The growth hormone (GH)/insulin-like growth factor (IGF) axis plays fundamental roles during development, maturation, and aging. Members of this axis, composed of various ligands, receptors, and binding proteins, are regulated in a tissue- and time-specific manner that requires precise control that is not completely understood. Some of the most recent advances in understanding the implications of this axis in human growth are derived from the identifications of new mutations in the gene encoding the pregnancy-associated plasma protein PAPP-A2 protease that liberates IGFs from their carrier proteins in a selective manner to allow binding to the IGF receptor 1. The identification of three nonrelated families with mutations in the PAPP-A2 gene has shed light on how this protease affects human physiology. This review summarizes our understanding of the implications of PAPP-A2 in growth physiology, obtained from studies in genetically modified animal models and the PAPP-A2 deficient patients known to date.

Adult height and long-term outcomes after rhIGF-1 therapy in two patients with PAPP-A2 deficiency

PAPP-A2 deficiency is a novel syndrome characterized by short stature due to low IGF bioactivity, skeletal abnormalities and decreased bone mineral density (BMD). Treatment with recombinant human IGF-1 (rhIGF-1) for 1 year demonstrated to increase growth velocity and BMD, without reported adverse effects, but data regarding the long-term efficacy and safety of rhIGF-1 administration in this entity has not yet been reported. Two Spanish siblings with short stature due to a homozygous loss-of-function mutation in the PAPP-A2 gene (p.D643fs25*) were treated with rhIGF-1 twice daily for six years. Growth velocity continued to increase and both patients achieved their target height. Free IGF-1 concentrations increased notably after rhIGF-1 administration, with serum IGFBP-3, IGFBP-5 and ALS levels also being higher during treatment. BMD was progressively normalized and an increase in lean mass was also noted during treatment. No episodes of hypoglycemia or any other adverse effects were documented. An increase in the growth of kidney and spleen length was observed in one of the patients.

Recovery of the maternal skeleton after lactation is impaired by advanced maternal age but not by reduced IGF availability in the mouse

Background

Lactation results in substantial maternal bone loss that is recovered following weaning. However, the mechanisms underlying this recovery, and in particular the role of insulin-like growth factor 1 (IGF-I), is not clear. Furthermore, there is little data regarding whether recovery is affected by advanced maternal age.

Methods

Using micro-computed tomography, we studied bone recovery following lactation in mice at 2, 5 and 7 months of age. We also investigated the effects of reduced IGF-I availability using mice lacking PAPP-A2, a protease of insulin-like growth factor binding protein 5 (IGFBP-5).

Results

In 2 month old mice, lactation affected femoral trabecular and cortical bone, but only cortical bone showed recovery 3 weeks after weaning. This recovery was not affected by deletion of the Pappa2 gene. The amount of trabecular bone was reduced in 5 and 7 month old mice, and was not further reduced by lactation. However, the recovery of cortical bone was impaired at 5 and 7 months compared with at 2 months.

Conclusions

Recovery of the maternal skeleton after lactation is impaired in moderately-aged mice compared with younger mice. Our results may be relevant to the long-term effects of breastfeeding on the maternal skeleton in humans, particularly given the increasing median maternal age at childbearing.

Short stature with low insulin-like growth factor 1 availability due to pregnancy-associated plasma protein A2 deficiency in a Saudi family

In 2016 a new syndrome with postnatal short stature and low IGF1 bioavailability caused by biallelic loss-of-function mutations in the gene encoding the metalloproteinase pregnancy-associated plasma protein A2 (PAPP-A2) was described in two families. Here we report two siblings of a third family from Saudi Arabia with postnatal growth retardation and decreased IGF1 availability due to a new homozygous nonsense mutation (p.Glu886* in exon 7) in PAPPA2. The two affected males showed progressively severe short stature starting around 8 years of age, moderate microcephaly, decreased bone mineral density, and high circulating levels of total IGF1, IGFBP3, and the IGF acid-labile subunit (IGFALS), with decreased free IGF1 concentrations. Interestingly, circulating IGF2 and IGFBP5 were not increased. An increase in growth velocity and height was seen in the prepuberal patient in response to rhIGF1. These patients contribute to the confirmation of the clinical picture associated with PAPP-A2 deficiency and that the PAPPA2 gene should be studied in all patients with short stature with this characteristic phenotype. Hence, pediatric endocrinologists should measure circulating PAPP-A2 levels in the study of short stature as very low or undetectable levels of this protein can help to focus the diagnosis and treatment.

Recombinant IGF-1 Induces Sex-Specific Changes in Bone Composition and Remodeling in Adult Mice with Pappa2 Deficiency

Deficiency of pregnancy-associated plasma protein-A2 (PAPP-A2), an IGF-1 availability regulator, causes postnatal growth failure and dysregulation of bone size and density. The present study aimed to determine the effects of recombinant murine IGF-1 (rmIGF-1) on bone composition and remodeling in constitutive Pappa2 knock-out (ko/ko) mice. To address this challenge, X-ray diffraction (XRD), attenuated total reflection-fourier transform infra-red (ATR-FTIR) spectroscopy and gene expression analysis of members of the IGF-1 system and bone resorption/formation were performed. Pappa2^ko/ko mice (both sexes) had reduced body and bone length. Male Pappa2^ko/ko mice had specific alterations in bone composition (mineral-to-matrix ratio, carbonate substitution and mineral crystallinity), but not in bone remodeling. In contrast, decreases in collagen maturity and increases in Igfbp3, osteopontin (resorption) and osteocalcin (formation) characterized the bone of Pappa2^ko/ko females. A single rmIGF-1 administration (0.3 mg/kg) induced short-term changes in bone composition in Pappa2^ko/ko mice (both sexes). rmIGF-1 treatment in Pappa2^ko/ko females also increased collagen maturity, and Igfbp3, Igfbp5, Col1a1 and osteopontin expression. In summary, acute IGF-1 treatment modifies bone composition and local IGF-1 response to bone remodeling in mice with Pappa2 deficiency. These effects depend on sex and provide important insights into potential IGF-1 therapy for growth failure and bone loss and repair.

Trabecular Bone Score in Children and Adolescents With Inflammatory Bowel Diseases

INTRODUCTION

Trabecular bone score (TBS) is a textural index that evaluates bone microarchitecture of the lumbar spine. Our aim was to assess TBS in children with inflammatory bowel diseases and to evaluate correlations with clinical, laboratory and densitometric variables.

METHODS

A retrospective study of TBS and areal bone mineral density measurements by dual-energy X-ray absorptiometry (DXA) of children with either Crohn's disease (CD) or ulcerative colitis (UC). Bone mineral apparent density was calculated for size adjustment. TBS Z-score for each child were calculated based on data from a healthy population of similar age and gender distribution. Variables significantly associated with TBS were included in stepwise linear regression models to examine independent predictors of TBS.

RESULTS

Fifty patients (age at DXA scan 13.8 ± 3.0 years, 29 males) were included. No significant differences were observed between the patients with CD and UC, in age at diagnosis, age at DXA scan and disease duration. The mean TBS of patients with CD (n = 35) was lower than of patients with UC (n = 15): 1.340 ± 0.080 vs 1.395 ± 0.092, p = 0.040. The mean TBS Z-score of patients with CD, -0.443 ± 0.788, was significantly lower than expected in healthy children (p = 0.002), while the mean TBS Z-score of patients with UC, 0.231 ± 0.685, was similar to that of healthy children (p = 0.212). In the stepwise linear regression analysis, BMI Z-score at diagnosis, phosphorus level at diagnosis and age at the time of the DXA scan were significant independent predictors of TBS (r² = 0.604; β = 0.037, 95% confidence interval (CI) for β 0.022-0.051, p < 0.001; β = 0.045, 95% CI: 0.017-0.073, p = 0.002; and β = 0.031, 95% CI: 0.005-0.021, p < 0.002, respectively).

CONCLUSIONS

TBS is significantly reduced in pediatric patients with CD but not in patients with UC. This finding likely reflects the effect of CD on bone microarchitecture.

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.

Disorders caused by genetic defects associated with GH-dependent genes: PAPPA2 defects

Growth hormone (GH) and its mediator, insulin-like growth factor-1 (IGF-1), have long been recognized as central to human growth physiology. IGF-1 is known to complex with IGF binding proteins as well as with the acid labile subunit (ALS) in order to prolong its half-life in circulation. Factors regulating the bioavailability of IGF-1 (i.e. the balance between free and bound IGF-1) were less well understood. Recently, pregnancy-associated plasma protein-A2 (PAPP-A2) was discovered as a protease which specifically cleaves IGF-binding protein (IGFBP)-3 and -5. PAPP-A2 deficient patients present with characteristic findings including growth failure, elevated total IGF-1 and -2, IGFBPs, and ALS, but decreased percentage of free to total IGF-1. Additionally, patients with PAPP-A2 deficiency have impairments in glucose metabolism and bone mineral density (BMD). Treatment with recombinant human IGF-1 (rhIGF-1) improved height SD scores, growth velocity, body composition, and dysglycemia. Mouse models recapitulate many of the human findings of PAPP-A2 deficiency. This review summarizes the function of PAPP-A2 and its contribution to the GH-IGF axis through an examination of PAPP-A2 deficient patients and mouse models, thereby emphasizing the importance of the regulation of IGF-1 bioavailability in human growth.

Update on methods to enhance growth

PURPOSE OF REVIEW

To discuss treatments used to enhance growth in pediatric patients with short stature.

RECENT FINDINGS

New data confirm the known efficacy of recombinant human growth hormone (rhGH) in growth hormone deficiency (GHD) and idiopathic short stature. The latest data from the Safety and Appropriateness of Growth hormone Treatment in Europe cohort did not indicate a long-term risk of malignancy in those treated for isolated GHD, but possibly increased risk in those with other diagnoses. Recombinant human insulin-like growth factor 1 is effective in treating patients with pregnancy-associated plasma protein A2 deficiency. Gonadotropin-releasing hormone agonists or aromatase inhibitor treatment to delay puberty remains controversial. They are more likely to augment adult height if combined with rhGH treatment in children already receiving rhGH. Preliminary data indicate that recombinant C-type natriuretic peptide (CNP) is safe in children and increases growth velocity upon 42 months of treatment in achondroplasia.

SUMMARY

Recent data confirms previous data on rhGH efficacy and safety. Therapies to delay growth plate closure have greatest efficacy to augment height if combined with GH in select diagnoses. Recombinant CNP holds promise as a medical treatment for short stature associated with achondroplasia.

Abnormal expression of Pappa2 gene may indirectly affect mouse hip development through the IGF signaling pathway

INTRODUCTION

Developmental dysplasia of the hip (DDH) is a major cause of disability in children, and the genetic mechanism of this disease remains unclear. In our previous study, we found that pregnancy-associated plasma protein-A2 (PAPP-A2) was associated with DDH significantly.

OBJECTIVES

The aim of this study was to investigate the insulin-like growth factor (IGF) expression and collagen synthesis as well as cartilage proliferation-related proteins in the case of abnormal expression of Pappa2 in mice to research the relationship between PAPP-A2 and the pathological changes of DDH.

METHODS

In vivo animal experiments, the mice were directly injected with 50 µl of Cas9/PAPP-A2 sgRNA lentiviruses around the hip to downregulate the Pappa2 gene expression and injected with control lentiviruses on the other side, then to observe the expression and localization of related proteins. And in an in vitro experiment, mice fibroblasts and primary chondrocytes were cultured with insulin-like growth factor binding protein-5 (IGFBP-5) protein, PAPP-A2 protein and Cas9/PAPP-A2 sgRNA lentiviruses to detect of related proteins and mRNA expression.

RESULTS

Cartilage proliferation-related proteins demonstrated a significant decrease in the PAPP-A2 knockdown hips acetabulum and femoral head cartilage, meanwhile the IGF expression was also downregulated in the soft tissue around the acetabulum compared with the control hips. Furthermore, the role PAPP-A2 played in chondrocytes and fibroblasts was the same as in the in vivo experiments, downregulation of PAPP-A2 expression or upregulation of IGFBP-5 expression can reduce collagen synthesis and cartilage proliferation.

CONCLUSIONS

PAPP-A2 may be involved in the development of the mouse hip joint by interfering the fibrous and cartilaginous metabolism via IGF pathway-associated proteins pathway.

Low IGF-I Bioavailability Impairs Growth and Glucose Metabolism in a Mouse Model of Human PAPPA2 p.Ala1033Val Mutation

Bioactive free IGF-I is critically important for growth. The bioavailability of IGF-I is modulated by the IGF-binding proteins (IGFBPs) and their proteases, such as pregnancy-associated plasma protein-A2 (PAPP-A2). We have created a mouse model with a specific mutation in PAPPA2 identified in a human with PAPP-A2 deficiency. The human mutation was introduced to the mouse genome via a knock-in strategy, creating knock-in mice with detectable protein levels of Papp-a2 but without protease activities. We found that the Pappa2 mutation led to significant reductions in body length (10%), body weight (10% and 20% in males and females, respectively), and relative lean mass in mice. Micro-CT analyses of Pappa2 knock-in femurs from adult mice showed inhibited periosteal bone expansion leading to more slender bones in both male and female mice. Furthermore, in the Pappa2 knock-in mice, insulin resistance correlated with decreased serum free IGF-I and increased intact IGFBP-3 concentrations. Interestingly, mice heterozygous for the knock-in mutation demonstrated a growth rate for body weight and length as well as a biochemical phenotype that was intermediate between wild-type and homozygous mice. This study models a human PAPPA2 mutation in mice. The mouse phenotype closely resembles that of the human patients, and it provides further evidence that the regulation of IGF-I bioavailability by PAPP-A2 is critical for human growth and for glucose and bone metabolism.

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.

Pappa2 deletion has sex- and age-specific effects on bone in mice

OBJECTIVE

In humans, loss-of-function mutations in the gene encoding pregnancy-associated pregnancy protein-A2 cause short stature and slightly reduced bone density. The goal of this study was to determine the effects of Pappa2 deletion on bone in mice.

DESIGN

Pappa2 deletion mice and littermate controls were culled at 10, 19 or 30 weeks of age and femurs were analysed by micro-computed tomography. Serum markers of bone turnover and insulin-like growth factor binding protein 5 (IGFBP-5), a proteolytic target of PAPP-A2, were measured by ELISA.

RESULTS

At 10 and 19 weeks of age, Pappa2 deletion mice had slightly reduced trabecular parameters, but by 19 weeks of age, female deletion mice had increased cortical tissue mineral density, and this trait was increased by a small amount in deletion mice of both sexes at 30 weeks. Cortical area fraction was increased in Pappa2 deletion mice at all ages. Deletion of Pappa2 increased circulating IGFBP-5 levels and reduced markers of bone turnover (PINP and TRACP 5b).

CONCLUSIONS

PAPP-A2 contributes to the regulation of bone structure and mass in mice, likely through control of IGFBP-5 levels. The net effect of changes in bone formation and resorption depend on sex and age, and differ between trabecular and cortical bone.

Genetics of Growth Disorders-Which Patients Require Genetic Testing?

The second 360° European Meeting on Growth Hormone Disorders, held in Barcelona, Spain, in June 2017, included a session entitled Pragmatism vs. Curiosity in Genetic Diagnosis of Growth Disorders, which examined current concepts of genetics and growth in the clinical setting, in terms of both growth failure and overgrowth. For patients with short stature, multiple genes have been identified that result in GH deficiency, which may be isolated or associated with additional pituitary hormone deficiencies, or in growth hormone resistance, primary insulin-like growth factor (IGF) acid-labile subunit deficiency, IGF-I deficiency, IGF-II deficiency, IGF-I resistance, and primary PAPP-A2 deficiency. While genetic causes of short stature were previously thought to primarily be associated with the GH-IGF-I axis, it is now established that multiple genetic anomalies not associated with the GH-IGF-I axis can result in short stature. A number of genetic anomalies have also been shown to be associated with overgrowth, some of which involve the GH-IGF-I axis. In patients with overgrowth in combination with an intellectual disability, two predominant gene families, the epigenetic regulator genes, and PI3K/AKT pathway genes, have now been identified. Specific processes should be followed for decisions on which patients require genetic testing and which genes should be examined for anomalies. The decision to carry out genetic testing should be directed by the clinical process, not merely for research purposes. The intention of genetic testing should be to direct the clinical options for management of the growth disorder.

Expression of PAPP-A2 and IGF Pathway-Related Proteins in the Hip Joint of Normal Rat and Those with Developmental Dysplasia of the Hip

Developmental dysplasia of the hip (DDH) is one of the major causes of child disability and early osteoarthritis. Genetic factors play an important role, but which still remain unclear. Pregnancy-associated plasma protein-A2 (PAPP-A2), a special hydrolase of insulin-like growth factor binding protein-5 (IGFBP-5), has been confirmed to be associated with DDH by previous studies. The aim of this study was firstly, to investigate the expression of PAPP-A2 and insulin-like growth factor (IGF) pathway-related proteins in normal rat's hip joints; secondly, to compare the variations of those proteins between DDH model rats and normal ones. The DDH model was established by swaddling the rat's hind legs in hip adduction and extension position. The hip joints were collected for expression study of fetal rats, normal newborn rats, and DDH model rats. Positive expression of PAPP-A2 and IGF pathway-related proteins was observed in all the hip joints of growing-stage rats. Ultimately, IGF1 was downregulated; insulin-like growth factor 1 receptor (IGF1R) showed an opposite trend in DDH rats when compared with normal group. The PAPP-A2 and IGF pathway-associated proteins may also be involved in the development of the rat's hip joint, which bring the foundation for further revealing the pathogenic mechanism of DDH.

Children Born Small for Gestational Age: Differential Diagnosis, Molecular Genetic Evaluation, and Implications

Children born small for gestational age (SGA), defined as a birth weight and/or length below -2 SD score (SDS), comprise a heterogeneous group. The causes of SGA are multifactorial and include maternal lifestyle and obstetric factors, placental dysfunction, and numerous fetal (epi)genetic abnormalities. Short-term consequences of SGA include increased risks of hypothermia, polycythemia, and hypoglycemia. Although most SGA infants show catch-up growth by 2 years of age, ∼10% remain short. Short children born SGA are amenable to GH treatment, which increases their adult height by on average 1.25 SD. Add-on treatment with a gonadotropin-releasing hormone agonist may be considered in early pubertal children with an expected adult height below -2.5 SDS. A small birth size increases the risk of later neurodevelopmental problems and cardiometabolic diseases. GH treatment does not pose an additional risk.

Metabolomics changes in patients with PAPP-A2 deficiency in response to rhIGF1 treatment

OBJECTIVE

Mutations in the pregnancy-associated plasma protein A2 (PAPP-A2) gene have recently been shown to cause postnatal growth failure in two prepubertal patients from a non-consanguineous Spanish family due to the resulting decrease in IGF1 bioavailability. Although a specific pharmacological treatment of this entity is yet to be established, both children received progressive subcutaneous doses (40 to 120 μg/kg) of rhIGF1 twice daily for 2 years. The improvements in growth, hyperinsulinemia and bone mineral density have been previously reported. The objective of this study was to analyze the changes in metabolism associated with these responses to rhIGF1 treatment.

DESIGN

Herein we present a detailed characterization of the acute and long-term changes in the metabolic profiles of these two siblings with PAPP-A2 deficiency after the initial injections of rhIGF1 and after two years of treatment.

RESULTS

By using a GC-MS-based untargeted metabolomics approach, metabolic fingerprinting yielded the identification of 70 serum metabolites including amino acids (46%), organic acids (21%) carbohydrates (16%), fatty acids (14%), and purine bases (3%). Free fatty acids (FFAs) and amino acids showed the largest changes in the compared metabolic profiles, suggesting that rhIGF1 treatment has the greatest effects on lipid and protein metabolic pathways in the PAPP-A2 deficient subjects.

CONCLUSIONS

The administration of rhIGF1 resulted in changes related to crucial metabolic pathways, including lipid and protein metabolism, and this could be associated with the previously reported treatment-induced improvement in the mild basal hyperinsulinemia.

Genetic causes of proportionate short stature

Human growth is a very complex phenomenon influenced by genetic, hormonal, nutritional and environmental factors, from fetal life to puberty. Although the GH-IGF axis has a central role with specific actions on growth, numerous genes are involved in the control of stature. Genome-wide association studies have identified >600 variants associated with human height, still explaining only a small fraction of phenotypic variation. Since short stature in childhood is a common reason for referral, pediatric endocrinologists must be aware of the multifactorial and polygenic contributions to height. Multiple disorders characterized by growth failure of prenatal and/or postnatal onset due to single gene defects have been described. Their early diagnosis, facilitated by advances in genomic technologies, is of upmost importance for their clinical management and to provide genetic counseling. Here we review the current clinical and genetic information regarding different syndromes and hormone abnormalities with proportionate short stature as the main feature, and provide an update of the approach for diagnosis and management.

Letter to the Editor: History and clinical implications of PAPP-A2 in human growth: When reflecting on idiopathic short stature leads to a specific and new diagnosis: Understanding the concept of "low IGF-I availability"

As a result of our publication of the first patients with short stature due to a mutation in the gene for PAPP-A2 the question, "Why did you continue to study these patients when they were not more than 2 SDS below normal?" has been proposed surprisingly frequently. We would like to communicate our opinions on why these patients were studied and share the experience on how this process took place. In addition, the choice of treatment is also discussed. We believe that this discovery process is a good example of good clinical practice and international collaboration.