[Biosimilars in the European Union: current situation and challenges]. / Biosimilars in der EU: Bestandsaufnahme und neue Herausforderungen.

Biosimilars are medicinal products that are highly similar to approved biopharmaceuticals. Biosimilars enable patient access to biological therapies that would otherwise be restricted or delayed due to cost reasons. After the successful introduction of low-molecular biosimilars in 2006, highly complex monoclonal antibodies have also been available since 2013 as biosimilars for treating autoimmune diseases and oncologic indications. In principle, the biosimilar concept can be applied to all well-characterized biologicals; in the future, blood clotting factors or drugs containing nucleic acids, such as DNA or RNA gene therapy or mRNA vaccines, will also be an option for biosimilar development.In some instances, biosimilarity can be demonstrated by physicochemical and functional similarity, and additional comparative clinical efficacy and safety studies have been considered no longer necessary for several product categories in recent years. Switching a patient from a reference drug to a biosimilar or from one biosimilar to another (interchangeability) has so far been considered harmless. Since February 2020, there has been a provisional decision in Germany that patients should be switched according to an economic prescription method. Further scientific findings on the interchangeability of biosimilars and experiences with the supply practices of biosimilars should be collected and evaluated.In this article, the current situation regarding marketing authorizations of biosimilars in the European Union is reviewed. The role of clinical trials for biosimilars is presented, and challenges of biosimilar development and views on interchangeability are discussed.

Biosimilars: the science of extrapolation.

Despite the establishment of a specific approval pathway, the issuance of detailed scientific guidelines for the development of similar biological medicinal products (so-called "biosimilars") and the approval of several biosimilars in the European Union, acceptance of biosimilars in the medical community continues to be low. This is especially true in therapeutic indications for which no specific clinical trials with the biosimilar have been performed and that have been licensed based on extrapolation of efficacy and safety data from other indications. This article addresses the concerns frequently raised in the medical community about the use of biosimilars in such extrapolated indications and explains the underlying scientific and regulatory decision making including some real-life examples from recently licensed biosimilars.

Biosimilars: what clinicians should know.

Biosimilar medicinal products (biosimilars) have become a reality in the European Union and will soon be available in the United States. Despite an established legal pathway for biosimilars in the European Union since 2005 and increasing and detailed regulatory guidance on data requirements for their development and licensing, many clinicians, particularly oncologists, are reluctant to consider biosimilars as a treatment option for their patients. Major concerns voiced about biosimilars relate to their pharmaceutical quality, safety (especially immunogenicity), efficacy (particularly in extrapolated indications), and interchangeability with the originator product. In this article, the members and experts of the Working Party on Similar Biologic Medicinal Products of the European Medicines Agency (EMA) address these issues. A clear understanding of the scientific principles of the biosimilar concept and access to unbiased information on licensed biosimilars are important for physicians to make informed and appropriate treatment choices for their patients. This will become even more important with the advent of biosimilar monoclonal antibodies. The issues also highlight the need for improved communication between physicians, learned societies, and regulators.

A Data Driven Approach to Support Tailored Clinical Programs for Biosimilar Monoclonal Antibodies.

Biosimilar monoclonal antibodies (mAbs) have been approved in the European Union since 2013 and have been demonstrated to reduce healthcare costs and to expand patient access. Biosimilarity is mainly established on the basis of demonstrated similarity of relevant quality attributes (QAs), determined by comprehensive physiochemical and functional analyses, and demonstration of bioequivalence. In addition, comparative efficacy/safety studies have been requested for all approved biosimilar mAbs so far, although the European Medicines Agency (EMA) Guidelines state that such confirmatory clinical trials may not be necessary in specific circumstances. In order to evaluate the degree of analytical similarity, how residual uncertainty regarding biosimilarity was resolved, and the value of clinical data, we analyzed the quality and clinical data packages for authorized adalimumab (7 products) and bevacizumab (5 products) biosimilars. The percentage of biosimilar batches meeting the similarity range for QAs, as defined by the biosimilar manufacturer based on a comprehensive characterization of the EU reference product (RP), was determined and clinical data were reviewed. Our analyses show that QAs of approved adalimumab and bevacizumab biosimilars have varying concordance with the EU-RP similarity range. In this study, we found that clinical efficacy data played a limited role in addressing quality concerns. Therefore, we encourage a regulatory review of the standards for clinical data requirements for mAb and fusion protein biosimilars. This study outlines a quality data driven approach for facilitating tailored clinical programs for biosimilars.

Do the Outcomes of Clinical Efficacy Trials Matter in Regulatory Decision-Making for Biosimilars?

BACKGROUND: There is an increasing body of evidence supporting a more flexible approach in clinical data requirements for the approval of more complex biosimilar substances such as monoclonal antibodies (mAbs). OBJECTIVE: The aim of this paper is to further analyse the role of quality/chemistry, manufacturing and controls (CMC) and clinical data for the conclusion on biosimilarity and the decision on marketing authorisation (MA). METHODS: In the present study, we analysed the MA applications (MAAs) of all 33 mAbs and three fusion proteins evaluated by the European Medicines Agency (EMA) between July 2012 and November 2022 with special emphasis on all submitted rituximab (four products) and trastuzumab (seven products) biosimilar candidates, including withdrawn applications. For the two withdrawn applications, the comparative efficacy trials suggested biosimilarity, but the quality/CMC package was not accepted by EMA. We therefore investigated whether a negative MAA outcome could have been predicted based on the evidence generated in the quality/CMC packages, regardless of clinical trial data. For this purpose, we reviewed the respective European Public Assessment Reports (EPARs) or withdrawal assessment reports, and the first regulatory assessments for all these 36 MAAs (i.e. day 120 of the centralized procedure), which are not publicly available. During EMA review, where significant issues are identified which would preclude a marketing authorisation, these issues are raised as questions to the applicant and are classified as major objections (MO). RESULTS: In 67% of cases, the outcome of the quality and clinical assessment was the same, i.e. both the quality and clinical assessments either supported approval or did not support approval. In 11% of cases, MO were identified in the quality part of the submission but not in the clinical data. In 22% of cases, MO were raised on the clinical data package but not on the quality data. However, we found no instance where seemingly negative clinical data, including failed efficacy trials, led to a negative overall decision. In each instance, the failure to confirm similar clinical performance in all investigated aspects was eventually viewed as not being related to the biosimilar per se but as being due to imbalances in the trial arms, immaturity of secondary endpoint results, change in the reference product, or even chance findings. Furthermore, when performing an in-depth analysis of the quality and clinical packages of trastuzumab and rituximab biosimilars, we found that in no case were clinical trial data necessary to resolve residual uncertainties regarding the quality part. CONCLUSION: The results further support the argument that sufficient evidence for biosimilarity can be obtained from a combination of analytical and functional testing and pharmacokinetic studies which may also generate immunogenicity data. This calls into question the usefulness of comparative efficacy studies for the purposes of regulatory decision-making when approving biosimilar mAbs and fusion proteins.

Regulatory Evaluation of Biosimilars: Refinement of Principles Based on the Scientific Evidence and Clinical Experience.

The World Health Organization (WHO) guidelines on evaluation of similar biotherapeutic products (SBPs; also called biosimilars) were adopted by the WHO Expert Committee on Biological Standardization (ECBS) in 2009. In 2019, the ECBS considered that a more tailored and potentially reduced clinical data package may be acceptable in cases where this was clearly supported by the available scientific evidence. The goal of this publication is to review the current clinical experience and scientific evidence and to provide an expert perspective for updating the WHO guidelines to provide more flexibility and clarity. As the first step, the relevant guidelines by other regulatory bodies were reviewed in order to identify issues that might help with updating the WHO guidelines. Next, a literature search was conducted for information on the long-term efficacy, safety, and immunogenicity of biosimilars to identify possible long-term problems. Finally, a search for articles concerning the role of clinical studies in the benefit-risk evaluation of biosimilars was conducted. The analysis of other guidelines suggested that the WHO guidelines may need more emphasis on the importance of the state-of-the-art physicochemical and structural comparability exercise and in vitro functional testing. The use of "foreign" reference product will also need clarifications. The value of in vivo toxicological tests in the development of biosimilars is questionable, and the non-clinical part needs revisions accordingly. The concepts of "totality of evidence," "stepwise development," and "residual uncertainty" were applied in the evaluation of the clinical sections of the guideline. The review of long-term safety and efficacy demonstrated the robustness of the current biosimilar development concept. The analysis of the roles of different development phases suggested that the large efficacy, safety, and immunogenicity studies are, in most cases, redundant. The residual uncertainty of safety, immunogenicity, and efficacy of biosimilars that has shaped the current regulatory guidelines is now substantially reduced. This will allow the re-evaluation of the non-clinical and clinical requirements of the current WHO main guideline. The shift of the relative impact of the development phases towards physico-chemical and in vitro functional testing will provide a relief to the manufacturers and new challenges to the regulators.

The EU Response to the Presence of Nitrosamine Impurities in Medicines.

The unexpected detection of nitrosamine impurities in human medicines has recently seen global regulators act to understand the risks of these contaminations to patients and to limit their presence. Over 300 nitrosamines are known, many of which are highly potent mutagenic carcinogens. Regulators first became aware of the presence of nitrosamines in EU medicines in 2018, with reports of detection of N-nitroso-dimethylamine (NDMA) in valsartan from one manufacturer. A subsequent EU review of all valsartan medicines was triggered by the European Medicines Agency (EMA) and was later extended to other angiotensin receptor blockers/sartans. A separate review was also started for ranitidine medicines. This was followed by an EU-wide examination of the risk of presence of nitrosamines in all human medicines. This article reflects on the investigation of the EU regulatory network into the presence of nitrosamines and the scientific knowledge informing recommendations for developers on how to limit nitrosamines in medicines.

Identifiability of Biologicals: An Analysis Using EudraVigilance, the European Union's Database of Reports of Suspected Adverse Drug Reactions.

The relevance of biological therapies for an increasing number of conditions is on the rise. Following the expiry of the initial period of market exclusivity, many of these successful therapies have seen the arrival of biosimilars on the market. The clear identification of the precise medicine responsible for an adverse drug reaction (ADR) report is an important element for pharmacovigilance, allowing timely detection of potential product-specific safety signals. We looked at the identifiability of biologicals up to the level of commercial product name in ADR reports received from European clinical practice between 2011 and December 2019. A good level of identification (91.5%) was observed overall, but at the same time a downward trend was observed in the last 5 years. This reduction in the level of identifiability of biological products (originators and biosimilars) at the commercial name level in general was driven by five widely used substances, whereas the identification of all other biologics stayed consistent over time (at over 90%). We observed that those five substances were used mostly within oncology. The introduction of the first biosimilar in the market did not appear to affect their identifiability. These results show that although the general level of identification at the commercial product name level in ADRs in Europe is robust and generally stable over time, decreasing trends can be down to a few commonly used substances, which need to be monitored to reverse the trend.

Metabolic abnormalities and cardiovascular risk factors in children with myositis.

OBJECTIVE: To characterize the metabolic abnormalities and risk factors for future cardiovascular disease in children with myositis. STUDY DESIGN: Seventeen patients with severe juvenile myositis, primarily referred because of refractory disease, were examined with standardized disease activity and damage measures. Body mass index, fasting insulin and lipid levels, 2-hour oral glucose tolerance test results, and cytokine levels were obtained. RESULTS: Most patients (71%) had blood pressures >75th percentile; 23.5% of patients had hypertension; and body mass index was >85th percentile in 47%. Metabolic abnormalities were also frequent: 41.2% had an elevated fasting insulin level, 47.1% had hypertriglyceridemia, and 25% met criteria for the metabolic syndrome. Although insulin resistance was common (on the basis of homeostasis model assessment and glucose-to-insulin ratio), insulin secretion appeared to be unaffected. Thigh muscle damage assessed with magnetic resonance imaging significantly correlated with fasting insulin level, glucose level, and glucose-to-insulin ratio. Glucose indices also correlated with the proinflammatory cytokines interleukin (IL)-2 and IL-12 and inversely with anti-inflammatory cytokines IL-1RA and IL-10. CONCLUSIONS: In this referral cohort of children with severe juvenile myositis, metabolic abnormalities and predictors of cardiovascular disease were common, suggesting an increased risk of future cardiovascular disease. Indicators of insulin resistance correlated with muscle damage on magnetic resonance imaging and proinflammatory cytokines and inversely with anti-inflammatory cytokines.

From bioequivalence to biosimilars: How much do regulators dare?

The main advantage of an abbreviated licensing pathway is the possibility of extrapolating efficacy and safety data from an original medicinal product to a subsequent "copy" version, thereby reducing the clinical development programme in particular. For small-molecule chemically synthesized generics, such an abbreviated licensing pathway was established decades ago, whereas it was only more recently implemented for similar biological medicinal products, so-called biosimilars. Clinicians and patients have repeatedly expressed concerns about the efficacy and safety of biosimilars, especially in 'extrapolated' indications for which no own clinical data have been generated. Generic drugs usually contain well-defined active ingredients whose "identity" with that of the originator, the so-called reference product, is easily verifiable. Biological substances are generally more complex and difficult to characterize. They are produced in living organisms and therefore naturally exhibit some intrinsic variability, i.e. microheterogeneity. Since the chosen expression system and the manufacturing conditions influence the quality characteristics of a biological substance, mostly its posttranslational modifications such as the glycosylation pattern, it is unlikely that two independent manufacturing processes can achieve completely identical biologicals. A biosimilar, especially if it is a glycoprotein, can therefore, at best, be highly similar to the reference product. It seems that the not-identical-but-(highly)-similar-paradigm for biosimilars is often not well understood and causes confusion. However, while at first glance an abridged approval pathway for biosimilars appears to be daring, it is in fact based on sound scientific reasoning. A biosimilar applicant has to provide a considerably larger package of comparative data than a generic applicant to ensure that the biosimilar can indeed rely, for the purpose of licensing, on the efficacy and safety experience gained with the reference product. While for a generic, the demonstration of similar in vitro dissolution and in vivo bioavailability (so-called 'bioequivalence') is sufficient to conclude therapeutic equivalence with the reference product, for a biosimilar, comparable physicochemical, biological and functional characteristics as well as efficacy and safety/immunogenicity with the reference product must be demonstrated. In addition, unlike generics, any extrapolation to other indications of the reference product must be scientifically justified. More than 10 years of successful clinical experience with biosimilars in the EU support the credibility of the scientific principles guiding the biosimilar concept. So far, there has been no need for either withdrawal of an approved biosimilar or for additional labelling because of efficacy or safety concerns.

Evolution of the EU Biosimilar Framework: Past and Future.

The approval of biosimilars in the EU follows a comprehensive scientific assessment based on stringent regulatory standards. While the initial approach to biosimilars was understandably cautious and conservative in that uncharted territory to protect patients' safety, the analytical and scientific progress and accumulated experience with biosimilars continues to reshape regulatory requirements, generally leading to a reduced burden of clinical trials. This trend is expected to continue, for example, by increasingly employing pharmacodynamic endpoints and biomarkers, but much work remains to make this happen, especially for complex molecules with several or unknown mechanisms of action. We reviewed the available guidance and European Public Assessment Reports (EPARs) of biosimilars approved in the EU via the centralised procedure. This review focuses on the nature and extent of clinical confirmation of biosimilarity considered necessary in addition to analytical and functional data. Cases with conflicting results from different parts of the comparability exercise are discussed, with the aim of identifying whether certain elements of the comparability exercise are more important than others in determining biosimilarity. Taken together, analytical and functional comparison is the foundation of any biosimilar development. In addition, pharmacokinetic similarity is an indispensable prerequisite for any biosimilar approval, so careful planning on behalf of the applicant is mandated to avoid potential failure of such studies, for example, because of large interindividual variability, underpowered trial designs or other methodological causes. Comparative pharmacokinetic studies are a basic requirement for biosimilar development and are usually more sensitive than clinical efficacy trials when detecting potential product-related differences. This may explain why a demonstration of equivalent efficacy could not overrule a finding of dissimilar pharmacokinetic profiles in two cases of biosimilar pegfilgrastim. However, the outcome of efficacy trials depends not only on drug exposure but also on proper pharmacological action of the biological substance in vivo. Therefore, the objectives of both types of studies differ. Efficacy trials should usually be designed as equivalence trials to ensure that the efficacy of the biosimilar is neither decreased nor increased compared with the reference product. However, some remaining uncertainty regarding potentially increased efficacy of the biosimilar may be acceptable in exceptional cases, provided that the data from other parts of the comparability exercise clearly support a conclusion of biosimilarity and safety is assured. In contrast, uncertainties regarding potentially inferior efficacy of the biosimilar may not be acceptable at all. We conclude that the EU biosimilar regulatory framework is robust and able to adapt to advancing knowledge and experience and to strike a balance between regulatory standards, patient safety and feasibility of biosimilar development.

Patients with classic congenital adrenal hyperplasia have decreased epinephrine reserve and defective glycemic control during prolonged moderate-intensity exercise.

CONTEXT: Patients with classic congenital adrenal hyperplasia (CAH) have adrenomedullary dysplasia and hypofunction, and their lack of adrenomedullary reserve has been associated with a defective glucose response to brief high-intensity exercise. OBJECTIVE: Our objective was to assess hormonal, metabolic, and cardiovascular response to prolonged moderate-intensity exercise comparable to brisk walking in adolescents with classic CAH. SUBJECTS AND METHODS: We compared six adolescents with classic CAH (16-20 yr old) with seven age-, sex-, and body mass index group-matched controls (16-23 yr old) using a 90-min standardized ergometer test. Metabolic, hormonal, and cardiovascular parameters were studied during exercise and recovery. RESULTS: Glucose did not change throughout exercise and recovery for controls, whereas CAH patients showed a steady decline in glucose during exercise with an increase in glucose in the postexercise period. Glucose levels were significantly lower in CAH patients at 60 (P = 0.04), 75 (P = 0.01), and 90 (P = 0.03) min of exercise and 15 (P = 0.02) min post exercise, whereas glucose levels were comparable between the two groups early in exercise and at 30 min (P = 0.19) post exercise. As compared with controls, CAH patients had significantly lower epinephrine (P = 0.002) and cortisol (P < or = 0.001) levels throughout the study and similar norepinephrine, glucagon, and GH levels. Patients with CAH and controls had comparable cardiovascular parameters and perceived level of exertion. Despite having lower glucose levels, insulin levels were slightly higher in CAH patients during the testing period (P = 0.17), suggesting insulin insensitivity. CONCLUSION: CAH patients have defective glycemic control and altered metabolic and hormonal responses during prolonged moderate-intensity exercise comparable to brisk walking.

Interchangeability of Biosimilars: A European Perspective.

Many of the best-selling 'blockbuster' biological medicinal products are, or will soon be, facing competition from similar biological medicinal products (biosimilars) in the EU. Biosimilarity is based on the comparability concept, which has been used successfully for several decades to ensure close similarity of a biological product before and after a manufacturing change. Over the last 10 years, experience with biosimilars has shown that even complex biotechnology-derived proteins can be copied successfully. Most best-selling biologicals are used for chronic treatment. This has triggered intensive discussion on the interchangeability of a biosimilar with its reference product, with the main concern being immunogenicity. We explore the theoretical basis of the presumed risks of switching between a biosimilar and its reference product and the available data on switches. Our conclusion is that a switch between comparable versions of the same active substance approved in accordance with EU legislation is not expected to trigger or enhance immunogenicity. On the basis of current knowledge, it is unlikely and very difficult to substantiate that two products, comparable on a population level, would have different safety or efficacy in individual patients upon a switch. Our conclusion is that biosimilars licensed in the EU are interchangeable.

Biosimilars: Here and Now.

Congress passed the Biologics Price Competition and Innovation Act (BPCI Act) as part of the Affordable Care Act on March 23, 2010. The BPCI Act authorized an approval pathway for biosimilar and interchangeable products. It defines biosimilarity to mean "that the biological product is highly similar to the reference product notwithstanding minor differences in clinically inactive components" and that "there are no clinically meaningful differences between the biological product and the reference product in terms of safety, purity, and potency of the product." The biosimilar pathway has the potential to facilitate access to biologic products through increased competition, in the same manner as biosimilars have done for almost 10 years in Europe. The goal of a biosimilar program is not to independently establish safety and effectiveness for each condition of use. Rather, the goal is to demonstrate biosimilarity through an extensive analytical characterization and a targeted clinical program designed to assess for clinically meaningful differences, if they exist. The regulatory approaches in both the United States and Europe involve a totality-of-the-evidence approach to demonstrate biosimilarity. Importantly, the biosimilar pathway allows for extrapolation of data across indications so that a sponsor, with adequate scientific justification, need not conduct clinical studies in each intended condition of use. Without extrapolation, development may not be feasible for many products, and patients and resources could be diverted from clinical studies of newer agents for cancer.

Recovery from osteoporosis through skeletal growth: early bone mass acquisition has little effect on adult bone density.

It is often assumed that bone mineral accretion should be optimized throughout childhood to maximize peak bone mass. In contrast, we hypothesized that bone mineral acquisition early in life would have little or no effect on adult bone mass because many areas of the juvenile skeleton are replaced in toto through skeletal growth. To test this hypothesis, we induced osteoporosis by administering dexamethasone to 5-week-old rabbits for 5 weeks and then allowed them to recover for 16 weeks. Tibial bone mineral density (ash weight/volume) was decreased in the dexamethasone-treated animals at the end of treatment but recovered completely. Bone structure in the femur was assessed by histomorphometry. Trabecular and cortical bone in the distal metaphysis was made osteoporotic by dexamethasone, but was then replaced through endochondral bone formation and recovered. Periosteal bone formation rate in the diaphysis was decreased during dexamethasone treatment but afterwards rebounded above controls and normalized cortical width. Our data suggest that bone mineral acquisition early in life has little effect on adult bone density because the juvenile bone is largely replaced through growth. If this concept generalizes, then interventions to maximize peak bone mass should be directed at adolescents rather than young children.

The role of the resting zone in growth plate chondrogenesis.

In mammals, growth of long bones occurs at the growth plate, a cartilage structure that contains three principal layers: the resting, proliferative, and hypertrophic zones. The function of the resting zone is not well understood. We removed the proliferative and hypertrophic zones from the rabbit distal ulnar growth plate in vivo, leaving only the resting zone. Within 1 wk, a complete proliferative and hypertrophic zone often regenerated. Next, we manipulated growth plates in vivo to place resting zone cartilage ectopically alongside the proliferative columns. Ectopic resting zone cartilage induced a 90-degree shift in the orientation of nearby proliferative zone chondrocytes and seemed to inhibit their hypertrophic differentiation. Our findings suggest that resting zone cartilage makes important contributions to endochondral bone formation at the growth plate: 1) it contains stem-like cells that give rise to clones of proliferative chondrocytes; 2) it produces a growth plate-orienting factor, a morphogen, that directs the alignment of the proliferative clones into columns parallel to the long axis of the bone; and 3) it may also produce a morphogen that inhibits terminal differentiation of nearby proliferative zone chondrocytes and thus may be partially responsible for the organization of the growth plate into distinct zones of proliferation and hypertrophy.

Pubertal and gender-related changes in the sympathoadrenal system in healthy children.

A critical amount of body fat is necessary for the initiation of puberty, and leptin, an adipocyte-derived hormone, is necessary for pubertal development. The sympathoadrenal system modulates body fat stores and leptin secretion and interacts with adrenocortical androgen production, suggesting a possible role in sexual maturation. We studied sympathetic nerve and adrenomedullary activity at rest in 80 healthy children (ages, 5-17 yr; 37 boys and 43 girls) in relation to age, pubertal stage, gender, physical activity, body mass index, and serum levels of sex steroids, dehydroepiandrosterone sulfate, cortisol, leptin, and insulin. Plasma concentrations of the adrenomedullary hormone, epinephrine (E), and its metabolite metanephrine (MN), decreased significantly with advancing puberty and were higher in boys than in girls. E and MN correlated significantly and inversely with dehydroepiandrosterone sulfate, estradiol, testosterone, leptin, and insulin. Plasma norepinephrine, which is primarily derived from sympathetic nerve endings, increased significantly with advancing puberty and increasing testosterone levels in boys. Stepwise multiple regression analysis revealed that E was best predicted by pubertal stage and leptin, and MN by estradiol and leptin. Our data suggest that sympathoadrenal hormones may play a role in the complex process of sexual maturation. Further studies are needed to investigate a possible modulatory role of the adrenal medulla in the body weight-related timing of adrenarche and/or gonadarche.

Utility of plasma free metanephrines for detecting childhood pheochromocytoma.

Measurements of plasma free metanephrines, normetanephrine (NMN) and metanephrine (MN), provide a sensitive test for diagnosis of pheochromocytoma in adults but have not been evaluated in children. We therefore established reference ranges for plasma and urinary metanephrines and the catecholamines, norepinephrine (NE) and epinephrine (E), in 86 healthy children (age 5-17). A group of 158 healthy adults (age 18-72) served as a comparison group. Pediatric reference ranges were applied to examine the diagnostic utility of the various tests in 45 children evaluated for pheochromocytoma (age 8-17; 38 with von Hippel-Lindau syndrome), with tumors found on 12 occasions. Upper reference limits for E and MN were higher and those for NE and NMN lower in children than in adults. Boys had higher plasma levels of E and MN and higher urinary excretion of all four amines than girls. Plasma free metanephrines provided a diagnostic test with values for sensitivity (100%) and specificity (94%) that were equal to or higher than those of other tests. In two children screened for pheochromocytoma on multiple occasions, use of pediatric reference ranges for plasma free metanephrines indicated the tumor a year earlier than indicated using adult reference ranges. The findings indicate that plasma free metanephrines provide a sensitive tool for detection of pheochromocytoma in children. Age appropriate reference ranges should be used and gender differences should be considered.

Determinants of growth during gonadotropin-releasing hormone analog therapy for precocious puberty.

In children with precocious puberty (PP), treatment with GnRH analogs (GnRHa) often decreases height velocity below normal. Based on previous animal studies, we hypothesized that this impaired growth is due to excessive advancement in growth plate senescence induced by the prior estrogen exposure. This hypothesis predicts that the height velocity during treatment will be inversely related to the severity of prior estrogen exposure. We analyzed data from 100 girls (age, 5.8 +/- 2.1 yr; mean +/- SD) with central PP who were treated with GnRHa. During GnRHa therapy, height velocity was low for age (-1.6 +/- 1.7 SD score; mean +/- SD). The absolute height velocity correlated most strongly with the bone age (BA), which we used as a surrogate marker for growth plate senescence (r = -0.727, P < 0.001). The severity of the growth abnormality (height velocity SD score for age) correlated inversely with markers of the severity of prior estrogen exposure, including duration of PP (r = -0.375, P < 0.001), Tanner breast stage (r = -0.220, P < 0.05), and BA advancement (r = -0.283, P < 0.01). Stepwise regression confirmed that BA was the best independent predictor of growth during GnRHa therapy. The findings are consistent with our hypothesis that impaired growth during GnRHa therapy is due, at least in part, to premature growth plate senescence induced by the prior estrogen exposure.

Children with classic congenital adrenal hyperplasia have elevated serum leptin concentrations and insulin resistance: potential clinical implications.

Leptin is secreted by the white adipose tissue and modulates energy homeostasis. Nutritional, neural, neuroendocrine, paracrine, and autocrine factors, including the sympathetic nervous system and the adrenal medulla, have been implicated in the regulation of leptin secretion. Classic congenital adrenal hyperplasia (CAH) is characterized by a defect in cortisol and aldosterone secretion, impaired development and function of the adrenal medulla, and adrenal hyperandrogenism. To examine leptin secretion in patients with classic CAH in relation to their adrenomedullary function and insulin and androgen secretion, we studied 18 children with classic CAH (12 boys and 6 girls; age range 2-12 yr) and 28 normal children (16 boys and 12 girls; age range 5-12 yr) matched for body mass index (BMI). Serum leptin concentrations were significantly higher in patients with CAH than in control subjects (8.1 +/- 2.0 vs. 2.5 +/- 0.6 ng/ml, P = 0.01), and this difference persisted when leptin values were corrected for BMI. When compared with their normal counterparts, children with CAH had significantly lower plasma epinephrine (7.1 +/- 1.3 vs. 50.0 +/- 4.2, P < 0.001) and free metanephrine concentrations (18.4 +/- 2.4 vs. 46.5 +/- 4.0, P < 0.001) and higher fasting serum insulin (10.6 +/- 1.4 vs. 3.2 +/- 0.2 microU/ml, P < 0.001) and testosterone (23.7 +/- 5.3 vs. 4.6 +/- 0.5 ng/dl, P = 0.003) concentrations. Insulin resistance determined by the homeostasis model assessment method was significantly greater in children with classic CAH than in normal children (2.2 +/- 0.3 vs. 0.7 +/- 0.04, P < 0.001). Leptin concentrations were significantly and negatively correlated with epinephrine (r = -0.50, P = 0.001) and free metanephrine (r = -0.48, P = 0.002) concentrations. Stepwise multiple linear regression analysis indicated that serum leptin concentrations were best predicted by BMI in both patients and controls. Gender predicted serum leptin concentrations in controls but not in patients with classic CAH. No association was found between the dose of hydrocortisone and serum leptin (r = -0.17, P = 0.5) or insulin (r = 0.24, P = 0.3) concentrations in children with CAH. Our findings indicate that children with classic CAH have elevated fasting serum leptin and insulin concentrations, and insulin resistance. These most likely reflect differences in long-term adrenomedullary hypofunction and glucocorticoid therapy. Elevated leptin and insulin concentrations in patients with CAH may further enhance adrenal and ovarian androgen production, decrease the therapeutic efficacy of glucocorticoids, and contribute to later development of polycystic ovary syndrome and/or the metabolic syndrome and their complications.