Further Evidence that an Episode of Premature Labor Is a Pathologic State: Involvement of the Insulin-Like Growth Factor System.

INTRODUCTION: Approximately 47% of women with an episode of preterm labor deliver at term; however, their infants are at greater risk of being small for gestational age and for neurodevelopmental disorders. In these cases, a pathologic insult may disrupt the homeostatic responses sustaining pregnancy. We tested the hypothesis of an involvement of components of the insulin-like growth factor (IGF) system. METHODS: This is a cross-sectional study in which maternal plasma concentrations of pregnancy-associated plasma protease (PAPP)-A, PAPP-A2, insulin-like growth factor-binding protein 1 (IGFBP-1), and IGFBP-4 were determined in the following groups of women: (1) no episodes of preterm labor, term delivery (controls, n = 100); (2) episode of preterm labor, term delivery (n = 50); (3) episode of preterm labor, preterm delivery (n = 100); (4) pregnant women at term not in labor (n = 61); and (5) pregnant women at term in labor (n = 61). Pairwise differences in maternal plasma concentrations of PAPP-A, PAPP-A2, IGFBP-1, and IGFBP-4 among study groups were assessed by fitting linear models on log-transformed data and included adjustment for relevant covariates. Significance of the group coefficient in the linear models was assessed via t-scores, with p < 0.05 deemed a significant result. RESULTS: Compared to controls, (1) women with an episode of premature labor, regardless of a preterm or a term delivery, had higher mean plasma concentrations of PAPP-A2 and IGFBP-1 (each p < 0.05); (2) women with an episode of premature labor who delivered at term also had a higher mean concentration of PAPP-A (p < 0.05); and (3) acute histologic chorioamnionitis and spontaneous labor at term were not associated with significant changes in these analytes. CONCLUSION: An episode of preterm labor involves the IGF system, supporting the view that the premature activation of parturition is a pathologic state, even in those women who delivered at term.

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.

Pregnancy-Associated Plasma Protein A2 in Hemodialysis Patients: Significance for Prognosis.

BACKGROUND: Pregnancy-associated plasma protein A (PAPP-A) is associated with adverse outcome of long-term hemodialysis patients (HD). The aim of the study was to test whether its homolog pregnancy-associated plasma protein A2 (PAPP-A2) can be detected in serum of HD patients and to define its significance. METHODS: The studied group consisted of 102 long-term HD patients and 25 healthy controls. HD patients were prospectively followed up for five years (2009-2014). PAPP-A2 was measured by surface plasmon resonance biosensor, PAPP-A by time resolved amplified cryptate emission. RESULTS: PAPP-A2, similarly as PAPP-A, was significantly increased in HD patients (median (interquartile range)) PAPP-A2: 6.2 (2.6-10.8) ng/mL, vs. 3.0 (0.7-5.9) ng/mL, p=0.006; PAPP-A: 18.9 (14.3-23.4) mIU/L, vs. 9.5 (8.4-10.5) mIU/L, p<0.001). In HD patients, PAPP-A2 correlated weakly but significantly with PAPP-A (τ=0.193, p=0.004). Unlike PAPP-A, PAPP-A2 was not significant for prognosis of HD patients when tested alone. There was a significant interaction between PAPP-A and PAPP-A2 on the mortality due to infection of HD patients (p=0.008). If PAPP-A was below median, mortality due to infection was significantly higher for patients with PAPP-A2 values above median than for patients with low PAPP-A2 levels (p=0.011). CONCLUSION: PAPP-A2 is increased in HD patients and interacts with PAPP-A on patients´ prognosis.

Papp-a2 modulates development of cranial cartilage and angiogenesis in zebrafish embryos.

Pregnancy-associated plasma protein A2 (PAPP-A2, also known as pappalysin-2) is a large metalloproteinase that is known to be required for normal postnatal growth and bone development in mice. We here report the detection of zebrafish papp-a2 mRNA in the chordamesoderm, notochord and lower jaw of zebrafish (Danio rerio) embryos, and that papp-a2-knockdown embryos display broadened axial mesoderm, notochord bends and severely reduced cranial cartilages. Genetic data link these phenotypes to insulin-like growth factor (Igf)-binding protein-3 (Igfbp-3) and bone morphogenetic protein (Bmp) signaling, and biochemical analysis show specific Igfbp-3 proteolysis by Papp-a2, implicating Papp-a2 in the modulation of Bmp signaling by Igfbp-3 proteolysis. Knockdown of papp-a2 additionally resulted in angiogenesis defects, strikingly similar to previous observations in embryos with mutations in components of the Notch system. Accordingly, we find that Notch signaling is modulated by Papp-a2 in vivo, and, furthermore, that human PAPP-A2 is capable of modulating Notch signaling independently of its proteolytic activity in cell culture. Based on these results, we conclude that Papp-a2 modulates Bmp and Notch signaling by independent mechanisms in zebrafish embryos. In conclusion, these data link pappalysin function in zebrafish to two different signaling pathways outside the IGF system.

Reduction in Pappalysin-2 Levels and Lower IGF-I Bioavailability in Female Adolescents With Anorexia Nervosa.

CONTEXT: Anorexia nervosa (AN) can cause severe undernutrition associated with alterations in the IGF axis. Pappalysins (PAPP-A, PAPP-A2) and stanniocalcins (STC-1, STC-2) modulate IGF binding-protein (IGFBP) cleavage and IGF bioavailability, but their implications in AN are unknown. OBJECTIVE: We determined serum levels of PAPP-As and STCs in relationship with classical IGF axis parameters in female adolescents with AN and their association with nutritional status and secondary amenorrhea. METHODS: Parameters of the IGF axis were determined in fasting serum samples of 68 female adolescents with AN at diagnosis and 62 sex- and age-matched controls. Standardized body mass index (BMI) and bone mineral density (BMD) were calculated. RESULTS: Patients with AN had lower concentrations of total and free IGF-I, total IGFBP-3, acid-labile subunit (ALS), insulin, PAPP-A2, STC-1, and STC-2 and higher levels of IGF-II and IGFBP-2. Their free/total IGF-I ratio was decreased and the intact/total IGFBP-3 and -4 ratios increased. BMI was directly related to total IGF-I and intact IGFBP-3 and inversely with IGFBP-2 and intact IGFBP-4. Weight loss was directly correlated with intact IGFBP-4 and negatively with intact IGFBP-3, ALS, STC-2, and PAPP-A2 concentrations. BMD was directly related to intact IGFBP-3 and inversely with intact IGFBP-4 and PAPP-A2 levels. Patients with amenorrhea had lower levels of total IGF-I and IGFBP-3 than those with menses. CONCLUSION: The reduction of PAPP-A2 in patients with AN may be involved in a decline in IGFBP cleavage, which could underlie the decrease in IGF-I bioavailability that is influenced by nutritional status and amenorrhea.

A robust immunoassay for pregnancy-associated plasma protein-A2 based on analysis of circulating antigen: establishment of normal ranges in pregnancy.

Pregnancy-associated plasma protein-A (PAPP-A) and PAPP-A2, two homologous metzincin metalloproteases, are both tightly linked to regulation within the insulin-like growth factor (IGF) system because of their specific cleavage of IGF binding proteins. Recent studies suggest that PAPP-A may be involved in clinical conditions related to unwanted cellular growth, and the circulating levels of PAPP-A is an established biomarker in prenatal screening for chromosomal abnormalities. Microarray data indicate that PAPP-A2 has potential as a biomarker for pre-eclampsia. However, well-characterized immunological methods of quantification are not available. We therefore developed monoclonal antibodies against recombinant PAPP-A2. The antibodies were epitope mapped against recombinantly expressed chimeras between PAPP-A2 and PAPP-A. Furthermore, circulating PAPP-A2 was immunoaffinity purified and characterized by sequence analysis and mass spectrometry. Unlike PAPP-A, PAPP-A2 is a noncovalent dimer in which each subunit of 1558 amino acids originates from all of the 22 predicted coding exons. A previously hypothesized variant (PAPP-E) does not exist, but low amounts of a C-terminally truncated PAPP-A2 variant was detected. A sensitive and robust ELISA for full-length PAPP-A2 was developed and used to establish normal ranges of PAPP-A2 through pregnancy. The functional sensitivity of this ELISA at 20% CV was 0.08 ng/ml, and the serum concentration of PAPP-A2 was found to increase during pregnancy in agreement with placental synthesis. The existence of this assay will enable an assessment of the biomarker potential of PAPP-A2 in pre-eclampsia as well as other clinical conditions.

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.

Clinical Application of a Graphene Oxide-Based Surface Plasmon Resonance Biosensor to Measure First-Trimester Serum Pregnancy-Associated Plasma Protein-A/A2 Ratio to Predict Preeclampsia.

Background: Preeclampsia, a major cause of adverse pregnancy outcomes, involves metalloproteinases pregnancy-associated plasma protein (PAPP)-A and PAPP-A2 from placental trophoblasts. The graphene oxide (GO)-based surface plasmon resonance (SPR) biosensor has higher sensitivity, affinity, and selective ability than the traditional SPR biosensor. The aim of this study was to explore the feasibility of measuring first-trimester serum PAPP-A/PAPP-A2 ratio as a novel predictor of preeclampsia using the GO-SPR biosensor. Methods: This prospective case-control study of pregnant women was conducted at MacKay Memorial Hospital, Taipei, Taiwan between January 2018 and June 2020. The SPR angle shifts of first-trimester serum PAPP-A, PAPP-A2, and PAPP-A/PAPP-A2 ratio measured using the GO-SPR biosensor were compared between preeclampsia and control groups. Results: Serum samples from 185 pregnant women were collected, of whom 30 had preeclampsia (5 early-onset; 25 late-onset). The response time between the antibody-antigen association and dissociation only took about 200 seconds. The SPR angle shift of PAPP-A in the preeclampsia group was significantly smaller than that in the control group (median (interquartile range): 5.33 (4.55) versus 6.89 (4.10) millidegrees (mDeg), P = 0.008). Conversely, the SPR angle shift of PAPP-A2 in the preeclampsia group was significantly larger than that in the control group (5.70 (3.81) versus 3.63 (2.38) mDeg, P < 0.001). Receiver operating characteristic (ROC) curve analysis revealed a cut-off PAPP-A/PAPP-A2 ratio to predict all preeclampsia of ≤ 0.76, with an area under the ROC curve (AUC) of 0.79 (95% CI 0.73-0.85, P < 0.001). Sub-group analysis revealed a cut-off PAPP-A/PAPP-A2 ratio to predict early-onset preeclampsia of ≤ 0.53 (AUC 0.99, 95% CI 0.96-1.00, P < 0.001), and ≤ 0.73 to predict late-onset preeclampsia (AUC 0.75, 95% CI 0.68-0.81, P < 0.001). Conclusion: Measuring first-trimester serum PAPP-A/PAPP-A2 ratio using the GO-SPR biosensor could be a valuable method for early prediction of preeclampsia.

Dynamic Changes in Serum IGF-I and Growth During Infancy: Associations to Body Fat, Target Height, and PAPPA2 Genotype.

CONTEXT: IGF-I is important for postnatal growth and may be of diagnostic value in infants suspected of pituitary disease; however, little is known about the impact of IGF-I and its determinants on infant growth. Importantly, detailed reference ranges for IGF-I and IGF binding protein-3 (IGFBP-3) concentrations during infancy are lacking. OBJECTIVE: To evaluate the rapid changes in weight and length as well as their determinants in healthy infants, and to establish age- and sex-specific reference curves for IGF-I and IGFBP-3 in children aged 0 to 1 years. DESIGN: Prospective longitudinal study. SETTING: Cohort study. PARTICIPANTS: A total of 233 healthy children (114 girls) with repeated blood samples during the first year of life. MAIN OUTCOME MEASURE(S): Serum concentrations of IGF-I and IGFBP-3, length velocity, weight velocity, and PAPPA2 (rs1325598) genotype. RESULTS: Individual trajectories of length and weight velocities were sex specific. We provide detailed reference curves based on longitudinal data for IGF-I and IGFBP-3 during infancy. In both girls and boys, IGF-I decreased during infancy, whereas IGFBP-3 remained stable. IGF-I and IGFBP-3, but not PAPPA2 genotype, were positively associated with weight gain, but not with longitudinal growth. When stratified by sex, the association between weight gain and IGF-I only remained significant in girls. CONCLUSIONS: Interestingly, we found a significant association between IGF-I and infant weight gain in girls, but not with longitudinal growth in the first year of life. Our findings highlight the role of IGF-I as an important anabolic hormone that is not limited to linear growth.

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.

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.

Immunoassay-Amplified Responses Using a Functionalized MoS2-Based SPR Biosensor to Detect PAPP-A2 in Maternal Serum Samples to Screen for Fetal Down's Syndrome.

BACKGROUND: Due to educational, social and economic reasons, more and more women are delaying childbirth. However, advanced maternal age is associated with several adverse pregnancy outcomes, and in particular a high risk of Down's syndrome (DS). Hence, it is increasingly important to be able to detect fetal Down's syndrome (FDS). METHODS: We developed an effective, highly sensitive, surface plasmon resonance (SPR) biosensor with biochemically amplified responses using carboxyl-molybdenum disulfide (MoS2) film. The use of carboxylic acid as a surface modifier of MoS2 promoted dispersion and formed specific three-dimensional coordination sites. The carboxylic acid immobilized unmodified antibodies in a way that enhanced the bioaffinity of MoS2 and preserved biorecognition properties of the SPR sensor surface. Complete antigen pregnancy-associated plasma protein-A2 (PAPP-A2) conjugated with the carboxyl-MoS2-modified gold chip to amplify the signal and improve detection sensitivity. This heterostructure interface had a high work function, and thus improved the efficiency of the electric field energy of the surface plasmon. These results provide evidence that the interface electric field improved performance of the SPR biosensor. RESULTS: The carboxyl-MoS2-based SPR biosensor was used successfully to evaluate PAPP-A2 level for fetal Down's syndrome screening in maternal serum samples. The detection limit was 0.05 pg/mL, and the linear working range was 0.1 to 1100 pg/mL. The women with an SPR angle >46.57 m° were more closely associated with fetal Down's syndrome. Once optimized for serum Down's syndrome screening, an average recovery of 95.2% and relative standard deviation of 8.5% were obtained. Our findings suggest that carboxyl-MoS2-based SPR technology may have advantages over conventional ELISA in certain situations. CONCLUSION: Carboxyl-MoS2-based SPR biosensors can be used as a new diagnostic technology to respond to the increasing need for fetal Down's syndrome screening in maternal serum samples. Our results demonstrated that the carboxyl-MoS2-based SPR biosensor was capable of determining PAPP-A2 levels with acceptable accuracy and recovery. We hope that this technology will be investigated in diverse clinical trials and in real case applications for screening and early diagnosis in the future.

PAPP-A2 and Inhibin A as Novel Predictors for Pregnancy Complications in Women With Suspected or Confirmed Preeclampsia.

Background We aimed to evaluate the value of inhibin A and PAPP-A2 (pregnancy-associated plasma protein-A2) as novel biomarkers in the prediction of preeclampsia-related complications and how they compare with angiogenic biomarkers. Methods and Results Making use of a secondary analysis of a prospective, multicenter, observational study, intended to evaluate the usefulness of sFlt-1 (soluble Fms-like tyrosine kinase-1)/PlGF (placental growth factor) ratio, we measured inhibin A and PAPP-A2 levels in 524 women with suspected/confirmed preeclampsia. Women had a median gestational age of 35 weeks (range, 20-41 weeks) while preeclampsia occurred in 170 (32%) women. Levels of inhibin A and PAPP-A2 were significantly increased in women with preeclampsia and in maternal perfusate of preeclamptic placentas. Inhibin A and PAPP-A2 (C-index = 0.73 and 0.75) significantly improved the prediction of maternal complications when added on top of the traditional criteria; gestational age, parity, proteinuria, and diastolic blood pressure (C-index = 0.60). PAPP-A2 was able to improve the C-index from 0.75 to 0.77 when added on top of the sFlt-1/PlGF ratio for the prediction of maternal complications. To discriminate fetal/neonatal complications on top of traditional criteria, inhibin A and PAPP-A2 showed additive value (C-index = 0.79 to 0.80 and 0.82, respectively) but their discriminative ability remained inferior to that of sFlt-1/PlGF ratio or PlGF. Interestingly, the PAPP-A2/PlGF ratio alone showed remarkable value to predict pregnancy complications, being superior to sFlt-1/PlGF ratio in the case of maternal complications. Conclusions Inhibin A and PAPP-A2 show significant potential to predict preeclampsia-related pregnancy complications and might prove beneficial on top of the angiogenic markers.

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.

Uteroplacental Ischemia Is Associated with Increased PAPP-A2.

Residence at high altitude (> 2500 m) has been associated with an increased frequency of preeclampsia. Pappalysin-2 (PAPP-A2) is an insulin-like growth factor binding protein-5 (IGFBP-5) protease that is elevated in preeclampsia, and up-regulated by hypoxia in placental explants. The relationships between PAPP-A2, altitude, and indices of uteroplacental ischemia are unknown. We aimed to evaluate the association of altitude, preeclampsia, and uterine artery flow or vascular resistance with PAPP-A2 levels. PAPP-A2, uterine artery diameter, volumetric blood flow, and pulsatility indices were measured longitudinally in normotensive Andean women residing at low or high altitudes in Bolivia and in a separate Andean high-altitude cohort with or without preeclampsia. PAPP-A2 levels increased with advancing gestation, with the rise tending to be greater at high compared to low altitude, and higher in early-onset preeclamptic compared to normotensive women at high altitude. Uterine artery blood flow was markedly lower and pulsatility index higher in early-onset preeclamptic normotensive women compared to normotensive women. PAPP-A2 was unrelated to uterine artery pulsatility index in normotensive women but positively correlated in the early-onset preeclampsia cases. We concluded that PAPP-A2 is elevated at high altitude and especially in cases of early-onset preeclampsia with Doppler indices of uteroplacental ischemia.

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.

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.

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

AIM: Our objective was to determine changes in bone mineral density (BMD), trabecular bone score (TBS), and body composition after 2 years of therapy with recombinant human insulin-like growth factor-1 (rhIGF-1) in 2 prepubertal children with a complete lack of circulating PAPP-A2 due to a homozygous mutation in PAPP-A2 (p.D643fs25*) resulting in a premature stop codon. METHODS: Body composition, BMD, and bone structure were determined by dual-energy X-ray absorptiometry at baseline and after 1 and 2 years of rhIGF-1 treatment. RESULTS: Height increased from 132 to 145.5 cm (patient 1) and from 111.5 to 124.5 cm (patient 2). Bone mineral content increased from 933.40 to 1,057.97 and 1,152.77 g in patient 1, and from 696.12 to 773.26 and 911.51 g in patient 2, after 1 and 2 years, respectively. Whole-body BMD also increased after 2 years of rhIGF-1 from baseline 0.788 to 0.869 g/cm2 in patient 1 and from 0.763 to 0.829 g/cm2 in patient 2. After 2 years of treatment, both children had an improvement in TBS. During therapy, a slight increase in body fat mass was seen, with a concomitant increase in lean mass. No adverse effects were reported. CONCLUSION: Two years of rhIGF-1 improved growth, with a tendency to improve bone mass and bone microstructure and to modulate body composition.

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.

PAPP-A2 a new key regulator of growth.

Short stature is the main problem that paediatric endocrinologists have to grapple with. Endocrine disorders account for only 5% of patients with short stature, but this is still one of the most common causes of reports to the endocrine clinic and hospitalisation in the endocrine department. A properly functioning growth hormone/insulin-like growth factor (GH/IGF) axis is one of the most important factors in proper growth. A lot of genetic defects in this axis lead to syndromes marked by impaired growth, like Laron syndrome, muta-tions in the STAT5B, insulin-like growth factor 1 (IGF1), and insulin-like growth factor 1 receptor (IGF1R) and mutations in the acid labile subunit (ALS). Two proteases important for the proper functioning of the GH/IGF axis: pregnancy-associated plasma protein-A (PAPP-A) and pregnancy-associated plasma protein-A2 (PAPP-A2), have been described. The first description of the new syndrome of growth failure associated with mutation in the PAPP-A2 gene was given by Andrew Dauber et al. This review evaluates the current data concerning PAPP-A2 function, and particularly the effect of PAPP-A2 mutation on growth.