Early Neonatal Administration of Vosoritide in Achondroplasia: A Report of Two Cases.

Vosoritide, a C-type natriuretic peptide analogue that inhibits FGFR3 signaling, is approved for the treatment of achondroplasia (ACH) from birth in Japan, Australia, and the United States; however, data on neonatal use remain limited. We report two infants with genetically confirmed ACH who received daily subcutaneous vosoritide starting on postnatal days 8 and 9, representing the earliest initiation reported to date. Both patients tolerated treatment in the short term without serious adverse events during inpatient or outpatient monitoring. Despite early initiation, serial magnetic resonance imaging demonstrated progressive foramen magnum stenosis during infancy, and both patients required decompression surgery at 9 and 5 months of age, respectively, consistent with the known natural history of ACH, with an uncomplicated postoperative course in both cases. Growth trajectories, assessed by growth velocity (GV), were generally above the ACH-specific reference medians at comparable ages, while the characteristic slowing of GV during infancy was preserved. These observations are descriptive and hypothesis-generating only and do not support changes in current clinical practice. Further data are required to clarify the potential benefits and limitations of initiating vosoritide therapy during the neonatal period.