Once-weekly TransCon CNP (navepegritide) in children with achondroplasia (ACcomplisH): a phase 2, multicentre, randomised, double-blind, placebo-controlled, dose-escalation trial

Advances in the mechanism and therapies of achondroplasia

Achondroplasia (ACH), is the prevailing type of genetic dwarfism in humans, caused by mutations in fibroblast growth factor receptor 3 (FGFR3) that are inherited in an autosomal dominant manner. FGFR3 is mainly expressed in condensed mesenchyme, chondrocytes, and mature osteoblasts and osteoclasts, in which it regulates the formation, development, growth, and remodeling of the skeletal system. Mutations in FGFR3 causing ACH result in enhanced FGFR3 signaling through combined mechanisms including enhancing FGF dimerization and tyrosine kinase activity and stabilizing FGF receptors. In ACH, suppression of the proliferation and maturation of chondrocytes in the growth plate leads to a notable reduction in growth plate size, trabecular bone volume, and bone elongation through a profound enhancement of FGFR3 signaling. This review aims to comprehensively outline the cellular and molecular mechanisms contributing to the pathological process of ACH and its potential therapeutic interventions.

[Significance and considerations of early diagnosis and treatment for improving height outcomes in children with achondroplasia]

Achondroplasia (ACH) is a common skeletal dysplasia in children, primarily caused by mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. These mutations disrupt the process of endochondral ossification in different types of bones, including long bones of the limbs and vertebrae. Children with ACH typically present with short stature and may experience severe multi-system complications. The diagnosis of ACH is based on typical clinical manifestations, imaging features, and genetic testing results. Treatment options mainly include pharmacological interventions and surgical procedures aimed at improving height, as well as symptomatic management for associated complications. This article discusses both prenatal and clinical diagnostic approaches for ACH, as well as treatment strategies focused on enhancing height, aiming to deepen the understanding of this condition.

Considerations for Anthropometry Specific to People with Disproportionate Short Stature

In the clinical care of people with disproportionate short stature, healthcare practitioners need to accurately collect anthropometric measurements over time, including height, weight, head circumference, and lengths of affected limb and body segments. Accurate anthropometric measurements are important for diagnostic evaluation, tracking growth, measuring response to pharmacologic therapies or surgeries, and monitoring for potential complications. However, for this clinical population, anthropometric measurements may need to be adjusted or modified to accommodate characteristics such as body disproportions, joint contractures, long bone deformities, spinal deformities, or muscle hypotonia. This article provides guidance for key anthropometric measurements in children and adults with disproportionate short stature, with a focus on people with achondroplasia. The measurements described in this article and illustrated in the infographics can be performed without expensive specialized equipment and are suitable for a variety of clinical settings.

Fgfr3 enhancer deletion markedly improves all skeletal features in a mouse model of achondroplasia

Achondroplasia, the most prevalent short-stature disorder, is caused by missense variants overactivating the fibroblast growth factor receptor 3 (FGFR3). As current surgical and pharmaceutical treatments only partially improve some disease features, we sought to explore a genetic approach. We show that an enhancer located 29 kb upstream of mouse Fgfr3 (-29E) is sufficient to confer a transgenic mouse reporter with a domain of expression in cartilage matching that of Fgfr3. Its CRISPR/Cas9-mediated deletion in otherwise WT mice reduced Fgfr3 expression in this domain by half without causing adverse phenotypes. Importantly, its deletion in mice harboring the ortholog of the most common human achondroplasia variant largely normalized long bone and vertebral body growth, markedly reduced spinal canal and foramen magnum stenosis, and improved craniofacial defects. Consequently, mouse achondroplasia is no longer lethal, and adults are overall healthy. These findings, together with high conservation of -29E in humans, open a path to develop genetic therapies for people with achondroplasia.

Current understanding and perspectives on growth and long-acting GH therapy in Japan

From the perspective of clinical pediatric endocrinology, progress in molecular biology over the past few decades has improved our understanding of growth physiology. This progress was particularly conspicuous in the early era of Sanger-based sequencing and has continued into the current era of next-generation sequencing. The first half of this review summarizes the current understanding about growth. The latter half discusses the development of long-acting GH (LAGH), an important, recent topic in pediatric endocrinology, with a focus on the Japanese market. LAGH is administered weekly over several years in some developed countries as treatment for GH deficiency (GHD). In Japan, somatrogon and somapacitan are available, and lonapegsomatropin has completed a clinical trial. As per recent meta-analyses, these three products were not inferior to conventional, daily GH therapy for short-term growth in pediatric GHD. Although LAGH is promising, some concerns remain. Well-designed clinical research is needed to expand the indications for LAGH to other conditions, such as idiopathic short stature. Finally, future research on orally administered agents may open new avenues for the treatment of short stature.

Progress in managing children with achondroplasia

INTRODUCTION

Achondroplasia is a heritable disorder of the skeleton that affects approximately 300,000 individuals worldwide. Until recently, treatment for this condition has been purely symptomatic. Efficacious treatment options for children are now approved or are in clinical trials.

AREAS COVERED

This review discusses key advances in the therapeutic management of children with achondroplasia, including vosoritide, the first approved drug, and other emerging precision therapies. These include navepegritide, a long-acting form of C-type natriuretic peptide, and infigratinib, a tyrosine kinase receptor inhibitor, summarizing trial outcomes to date.

EXPERT OPINION

The advent of the first approved precision therapy for achondroplasia in vosoritide has been a paradigm shifting advance for children affected by this condition. In addition to changing their natural growth history, it is hoped that it will decrease their medical complications and enhance functionality. These new treatment options highlight the importance of prompt prenatal identification and subsequent testing of a suspected fetus with achondroplasia and counseling of families. It is hoped that, in the near future, families will have the option to consider a range of effective targeted therapies that best suit their child with achondroplasia, starting from birth should they choose.

C-type natriuretic peptide (CNP): The cardiovascular system and beyond

C-type natriuretic peptide (CNP) represents the 'local' member of the natriuretic peptide family, functioning in an autocrine or paracrine capacity to modulate a hugely diverse portfolio of physiological processes. Whilst the best-characterised of these regulatory roles are in the cardiovascular system, akin to its predominantly endocrine siblings atrial (ANP) and brain (BNP) natriuretic peptides, CNP governs many additional, unrelated mechanisms including bone growth, gamete maturation, auditory processing, and neuronal integrity. Furthermore, there is currently great interest in mimicking the biological activity of CNP for therapeutic gain in many of these disparate organ systems. Herein, we provide an overview of the physiology, pathophysiology and pharmacology of CNP in both cardiovascular and non-cardiovascular settings.

Promising horizons in achondroplasia along with the development of new drugs

Achondroplasia (ACH) is a representative skeletal disorder characterized by rhizomelic shortened limbs and short stature. ACH is classified as belonging to the fibroblast growth factor receptor 3 (FGFR3) group. The downstream signal transduction of FGFR3 consists of STAT1 and RAS/RAF/MEK/ERK pathways. The mutant FGFR3 found in ACH is continuously phosphorylated and activates downstream signals, resulting in abnormal proliferation and differentiation of chondrocytes in the growth plate and cranial base synchondrosis. A patient registry has been developed and has contributed to revealing the natural history of ACH patients. Concerning the short stature, the adult height of ACH patients ranges between 126.7-135.2 cm for men and 119.9-125.5 cm for women in many countries. Along with severe short stature, foramen magnum stenosis and spinal canal stenosis are major complications: the former leads to sleep apnea, breathing disorders, myelopathy, hydrocephalus, and sudden death, and the latter causes pain in the extremities, numbness, muscle weakness, movement disorders, intermittent claudication, and bladder-rectal disorders. Growth hormone treatment is available for ACH only in Japan. However, the effect of the treatment on adult height is not satisfactory. Recently, the neutral endopeptidase-resistant CNP analogue vosoritide has been approved as a new drug for ACH. Additionally in development are a tyrosine kinase inhibitor, a soluble FGFR3, an antibody against FGFR3, meclizine, and the FGF2-aptamer. New drugs will bring a brighter future for patients with ACH.

New treatments for children with achondroplasia

Achondroplasia is the most common form of dwarfism in humans, caused by a common pathogenic variant in the gene encoding fibroblast growth factor receptor 3, FGFR3, which impairs the process of endochondral ossification of the growing skeleton. In this Review, we outline the clinical and genetic hallmarks of achondroplasia and related FGFR3 conditions, the natural history and impact of achondroplasia over a patient's lifespan, and diagnosis and management options. We then focus on the new and emerging drug therapies that target the underlying pathogenesis of this condition. These new options are changing the natural growth patterns of achondroplasia, with the prospect of better long-term health outcomes for patients.