Literature review and expert opinion on the impact of achondroplasia on medical complications and health-related quality of life and expectations for long-term impact of vosoritide: a modified Delphi study

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.

Exploring the family experience of children aged 2-4 years receiving daily vosoritide injections: A qualitative study

PURPOSE

Vosoritide is administered as a daily subcutaneous injection in children with achondroplasia. In clinical trials, families of children aged 2-4 years reported difficulty with drug administration due to child fear, pain, and distress. Study aims were to gain a better understanding of the current vosoritide administration experience in this cohort and to investigate whether topical anaesthesia and ice application prior to injections improved the child and family experience.

DESIGN AND METHODS

A qualitative descriptive study design ensured in-depth understanding of family experience. Parents were interviewed to explore experience of vosoritide administration for their child at two time points, before (Phase 1) and after (Phase 2) the introduction of topical anaesthesia and ice application prior to injections. Interviews were analysed using thematic analysis.

RESULTS

Seven families participated. Children's ages ranged from 2 years 2 months to 3 years 11 months. Five themes emerged from data analysis: (1) The reality of the burden of care; (2) Child experience as the greatest obstacle; (3) Parents juggle multiple emotional considerations; (4) Many factors may impact experience; and (5) Short-term and long-term impacts.

CONCLUSIONS

Administration of vosoritide in this cohort presents multiple challenges for families. Factors which influenced experience differed between families. Responses to topical anaesthesia and ice application also varied between children, improving administration experience for some children and worsening experience for others.

PRACTICE IMPLICATIONS

This study highlights the need for individualised care for young children receiving daily injections. Support should be provided to families to identify factors that improve experience.

The Treatment of Growth Disorders in Childhood and Adolescence

BACKGROUND

3% of all children are unusually short, and 3% are unusually tall. New approaches have broadened the range of therapeutic options in treating growth disorders.

METHODS

This review is based on publications retrieved by a selective review of the literature and on the authors' clinical experience.

RESULTS

Pituitary growth hormone deficiency is treated with recombinant growth hormone. Long-acting preparations of this type became available recently, but their long-term safety and efficacy are still unknown. Vosoritide, a CNP analogue, has also been approved for the treatment of achondroplasia, and severe primary deficiency of insulin-like growth factor 1 (IGF-1) can be treated with recombinant IGF-1. In the treatment of excessively tall stature, new information on the safety of growth-attenuating treatment and an altered perception of above-average height in society have led to a change in management.

CONCLUSION

There are new options for the treatment of rare causes of short stature, while new information on the safety of treatment strategies for excessive tallness have led to a reconsideration of surgical intervention. There is insufficient evidence on the benefits and risks of supraphysiological GH therapy and of newer treatment options for which there are as yet no robust data on adult height. Therefore, before any treatment is provided, physicians should give patients and their families detailed information and discuss their expectations from treatment and the goals that treatment can be expected to achieve.

Combined achondroplasia and short stature homeobox-containing (SHOX) gene deletion in a Danish infant

Short stature or shortening of the limbs can be the result of a variety of genetic variants. Achondroplasia is the most common cause of disproportionate short stature and is caused by pathogenic variants in the fibroblast growth factor receptor 3 gene (FGFR3). Short stature homeobox (SHOX) deficiency is caused by loss or defects of the SHOX gene or its enhancer region. It is associated with a spectrum of phenotypes ranging from normal stature to Léri-Weill dyschondrosteosis characterized by mesomelia and short stature or the more severe Langer mesomelic dysplasia in case of biallelic SHOX deficiency. Little is known about the interactions and phenotypic consequences of achondroplasia in combination with SHOX deficiency, as the literature on this subject is scarce, and no genetically confirmed clinical reports exist. We present the clinical findings in an infant girl with concurrent achondroplasia and SHOX deficiency. We conclude that the clinical findings in infancy are phenotypically compatible with achondroplasia, with no features of the SHOX deficiency evident. This may change over time, as some features of SHOX deficiency only become evident later in life.

Emerging therapies for the treatment of rare pediatric bone disorders

In recent years, new therapies for the treatment of rare pediatric bone disorders have emerged, guided by an increasing understanding of the genetic and molecular etiology of these diseases. Herein, we review three such disorders, impacted by debilitating deficits in bone mineralization or cartilage ossification, as well as the novel disease-modifying drugs that are now available to treat these conditions. Specifically, we discuss asfotase alfa, burosumab-twza, and vosoritide, for the treatment of hypophosphatasia, X-linked hypophosphatemia and achondroplasia, respectively. For each skeletal disorder, an overview of the clinical phenotype and natural history of disease is provided, along with a discussion of the clinical pharmacology, mechanism of action and FDA indication for the relevant medication. In each case, a brief review of clinical trial data supporting drug development for each medication is provided. Additionally, guidance as to drug dosing and long-term monitoring of adverse events and pediatric efficacy is presented, to aid the clinician seeking to utilize these novel therapies in their practice, or to become familiar with the healthcare expectations for children receiving these medications through specialized multidisciplinary clinics. The availability of these targeted therapies now significantly augments treatment options for conditions in which past therapy has relied upon less specific, symptomatic medical and orthopedic care.