Regulation of Childhood Growth
- Jeffrey Baron, MD, Head, Section on Growth and Development
- Kevin Barnes, PhD, Senior Research Assistant
- Julian Lui, PhD, Research Fellow
- Youn Hee Jee, MD, Clinical Scholar
- Michal Ad, BS, Postbaccalaureate Fellow
- Max Colbert, BA, Postbaccalaureate Fellow
- Melissa Jennings, BS, Postbaccalaureate Fellow
- Shanna Yue, BA, Postbaccalaureate Fellow
We investigate the cellular and molecular mechanisms governing childhood growth and development. We focus particularly on growth at the growth plate, which drives bone elongation and therefore determines height. One goal of this work is to gain insight into the many human genetic disorders that cause childhood growth failure or overgrowth. A second goal is to develop new treatments for children with severe growth disorders.
Identifying genes responsible for childhood growth disorders
Children grow taller because their bones grow longer. Bone elongation occurs at the growth plate, a thin layer of cartilage found near the ends of juvenile bones. Within the growth plates, chondrocyte proliferation, hypertrophy, and cartilage matrix production result in chondrogenesis, the production of new cartilage. The newly formed cartilage is subsequently remodeled into bone. The net result is that new bone is progressively created, resulting in bone elongation. Consequently, mutations in genes that regulate growth-plate chondrogenesis cause abnormal bone growth in children (Reference 1). Depending on the severity and nature of the genetic abnormality, the clinical phenotype can range from chondrodysplasias with short, malformed bones, to severe, often disproportionate, short stature, to mild proportionate short stature (Reference 1). If the genetic defect affects tissues other than the growth-plate cartilage, the child may present with a more complex syndrome that includes other clinical abnormalities (Reference 1). For many children who are brought to medical attention for linear growth disorders, clinical evaluation and laboratory evaluation fail to identify the underlying etiology. Genome-wide association studies, which we have helped analyze (Reference 2; Wood AR et al., Nat Genet 2014;46:1173-1186), and molecular-biological studies of growth-plate biology suggest that there are hundreds of genes that control linear growth. Therefore, it is likely that there are many genetic causes of linear growth disorders still to be discovered.
To discover new genetic causes of childhood growth disorders, we are using powerful genetic approaches, including single-nucleotide polymorphism (SNP) arrays to detect large deletions, duplications, mosaicism, and uniparental disomy, combined with exome sequencing to detect single-nucleotide variants and small insertions/deletions in coding regions and splice sites. The analysis led to our identification of heterozygous mutations in ACAN, the gene encoding aggrecan, which cause autosomal dominant short stature with advanced bone age and premature osteoarthritis (Nilsson O et al., J Clin Endocrinol Metab 2014;99:E1510-8.). We are participating in a multi-center collaboration to identify new families with this disorder in order to better characterize the clinical manifestations. We also identified compound heterozygous mutations in the BRF1 gene (which encodes one of the three subunits of the RNA polymerase III transcription factor complex) in a family with autosomal recessive growth failure, markedly delayed bone age, and central nervous system anomalies, confirming a previous report that BRF1 mutations cause cerebellar-facial-dental syndrome and further elucidating the phenotype. We also studied a subject with markedly accelerated skeletal and dental development, retinal scarring, and autism-spectrum disease and found elevated retinoic acid levels and a microdeletion on chromosome 18 10q23.2-23.33 that included the genes CYP26A1 and CYP26C1, which both encode major retinoic acid–metabolizing enzymes (Reference 3). Given that retinoic acid accelerates skeletal development and is involved in development of the eye and central nervous system, it is likely that these gene deletions contribute to the patient’s disorder.
Exploring the links between childhood growth and oncogenesis
Many of the mechanisms that regulate mammalian body growth can, when disrupted, contribute to the development of malignancies. We studied the role of two heparin-binding growth factors, pleiotrophin and midkine, in the regulation of both normal body growth and in unregulated growth of malignancies.
To delineate the role of midkine and pleiotrophin in human development, we developed high-sensitivity assays to measure their concentrations in amniotic fluid at various gestational ages in both healthy and complicated pregnancies (Reference 4). We found that both growth factors could be readily measured in amniotic fluid and that the concentrations were higher than most cytokines previously reported in amniotic fluid. The concentration of midkine, but not that of pleiotrophin, declined with gestational age. We found both midkine and pleiotrophin concentrations to be lower in pregnancies that were complicated by chorioamnionitis at term, raising the possibility that the growth factors could be useful as markers for infection.
Previously, we measured midkine concentrations in fine-needle aspirate (FNA) samples from benign and malignant thyroid nodules to explore the possibility that midkine measurement might aid in the evaluation of thyroid nodules. We found that, in FNA samples, the midkine/thyroglobulin ratio in papillary thyroid cancer was greater than in benign thyroid nodules (Jee YH et al., Clin Endocrinol (Oxf) 2015;83:977-984). More recently, we performed an analogous study of pleiotrophin and found that the pleiotrophin to thyroglobulin ratio was also higher in papillary thyroid cancer samples than in benign thyroid nodules (Reference 5). Thus, measurement of midkine and pleiotrophin concentrations in fine-needle aspirate samples may provide useful diagnostic and/or prognostic information in the evaluation of thyroid nodules.
Developing targeted treatment approaches for growth-plate disorders
Currently, treatment approaches for linear growth disorders are limited. The principal treatment approach is administration of recombinant growth hormone, but it has limited efficacy for severe disease, including many skeletal dysplasias, and has significant known and potential adverse effects. Therefore, better treatments for severe growth disorders are needed. Studies by our lab and many other labs have identified several paracrine factors that stimulate growth plate chondrogenesis and might therefore be used therapeutically. However, the therapeutic use of such molecules is challenging because they are produced locally and act locally in the growth plate, and thus do not lend themselves to systemic approaches. We hypothesized that these locally acting molecules could be targeted to the growth plate by linking them to cartilage-binding antibody fragments. When administered systemically, the hybrid molecules would be preferentially taken up by growth-plate cartilage, and thus might augment the therapeutic effect on the target organ while diminishing adverse effects from actions on other tissues. Similarly, growth-stimulating endocrine signals, such as growth hormone and insulin-like growth factor-I, might be targeted to the growth plate to increase the therapeutic effects on the growth plate and reduce adverse effects on other tissues. To develop a cartilage-targeting therapy, we used yeast display to identify antibody fragments that bound with high affinity to matrilin-3, an extracellular matrix protein expressed with high tissue specificity in cartilage (Reference 6). In vivo, the antibody fragments homed specifically to cartilage tissue in mice. Linking the antibody fragments to endocrine and paracrine factors that stimulate growth-plate chondrogenesis may open up new pharmacological approaches to treat childhood skeletal growth disorders.
Currently, we are constructing fusion proteins that combine matrilin-3–binding antibody fragments and paracrine factors that stimulate growth plate chondrogenesis. We are testing these fusion proteins in vitro and in vivo to determine their ability to bind to growth-plate cartilage, to interact with the relevant cell-surface receptors, and to increase growth-plate chondrogenesis without engendering significant off-target effects.
Additional Funding
- Thrasher Research Fund Early Career Award to Youn Hee Jee (2014, ongoing): “The Role of Heparin Binding Growth Factors in Fetal and Childhood Growth”
- Clinical Center Genomic Opportunity Program (2104, ongoing): “Genetic Causes of Childhood Growth Failure”
- Merck-Serono Grant for Growth Innovation to Julian Lui (2014, ongoing): “Cartilage-Targeted Therapeutics for Growth Disorders”
- Endocrine Scholars Award in Growth Hormone Research to Julian Lui (2015, ongoing): “Cartilage-Targeted IGF-I for Treatment of Growth Disorders”
- Pediatric Endocrine Society Clinical Scholar Award to Youn Hee Jee (2016, ongoing): “The role of PSD-93 in the initiation of puberty and in the etiology of pubertal delay”
Publications
- Baron J, Sävendahl L, Phillip M, De Luca F, Dauber A, Wit JM, Nilsson O. Short and tall stature: a new paradigm emerges. Nat Rev Endocrinol 2015;11:735-746.
- Pers TH, Karjalainen JM, Chan Y, Westra HJ, Wood AR, Yang J, Lui JC, Vedantam S, Gustafsson S, Esko T, Frayling T, Speliotes EK, Genetic Investigation of ANthropometric Traits (GIANT) Consortium, Boehnke M, Raychaudhuri S, Fehrmann RS, Hirschhorn JN, Franke L. Biological interpretation of genome-wide association studies using predicted gene functions. Nat Commun 2015;6:5890.
- Nilsson O, Isoherranen N, Guo MH, Lui JC, Jee YH, Guttmann-Bauman I, Acerini C, Lee W, Allikmets R, Yanovski JA, Dauber A, Baron J. Accelerated skeletal maturation in disorders of retinoic acid metabolism: a case report and focused review of the literature. Horm Metab Res 2016;48(11):737-744.
- Jee YH, Lebenthal Y, Chaemsaithong P, Yan G, Sacks DB, Wellstein A, Romero R, Baron J. Midkine and pleiotrophin concentrations in amniotic fluid in healthy and complicated pregnancies. PLoS One 2016;11:e0153325.
- Jee YH, Sadowski SM, Xi L, Raffeld M, Celi FS, Sacks DB, Remaley AT, Wellstein A, Kebebew E, Baron J. Increased pleiotrophin concentrations in papillary thyroid cancer. PLoS One 2016;11:e0149383.
- Cheung CS, Zhu Z, Lui JC, Dimitrov D, Baron J. Human monoclonal antibody fragments targeting matrilin-3 in growth plate cartilage. Pharm Res 2015;32:2439-2449.
Collaborators
- Francesco Celi, MD, Virginia Commonwealth University, Richmond, VA
- Andrew Dauber, MD, Boston Children’s Hospital, Boston, MA
- Angela Delaney, MD, Unit on Genetics of Puberty and Reproduction, NICHD, Bethesda, MD
- Dimiter Dimitrov, PhD, Laboratory of Experimental Immunology, Center for Cancer Research, NCI, Frederick, MD
- Joel Hirschhorn, MD, PhD, Harvard Medical School, Boston, MA
- Alexander A. Jorge, MD, Universidade de São Paulo, São Paulo, Brazil
- Electron Kebebew, MD, Endocrine Oncology Branch, Center for Cancer Research, NCI, Bethesda, MD
- Thomas Markello, MD, PhD, Undiagnosed Diseases Program, NHGRI, Bethesda, MD
- Ola Nilsson, MD, PhD, Karolinska Institute, Stockholm, Sweden
- Alan Remaley, MD, PhD, Cardiovascular and Pulmonary Branch, NHLBI, Bethesda, MD
- Katherine W. Roche, PhD, Receptor Biology Section, NINDS, Bethesda, MD
- Roberto Romero, MD, DMedSci, Perinatology Research Branch, NICHD, Detroit, MI
- David B. Sacks, MBChB, FRCPath, Department of Laboratory Medicine, Clinical Center, NIH, Bethesda, MD
- Anton Wellstein, PhD, Georgetown University Medical Center, Washington, DC
- Jan-Maarten Wit, MD, Universiteit Leiden, Leiden, The Netherlands
- Jack Yanovski, MD, PhD, Section on Growth and Obesity, NICHD, Bethesda, MD
Contact
For more information, email jbaron@mail.nih.gov or visit baron.nichd.nih.gov.
