A Study to Learn About Recifercept in Patients With Achondroplasia

Inclusion Criteria: * All patients from Study C4181005 who have completed Visits 1 through 11 (at D183) will be included in this project. To construct a concurrent external control, patients from Study C4181001 will need to meet the following inclusion criteria from Study C4181005 to be eligible for inclusion: * Documented, confirmed genetic diagnosis of achondroplasia from historical medical records (test must have been performed at a laboratory fully accredited for genetic testing under local regulations) * Aged ≥ 3 months to \<11 years (up to the day before 11th birthday inclusive) at time of enrollment into the observational natural history study. * Havecompleted at least 2 valid height/length measurements (at least 3 months apart) * Assessed for Tanner stage 1 during physical examination before or at enrollment (must include assessment of breast development for females, testicular stage for males) * Able to stand independently for height measurements (if ≥ 2 years of age at enrollment); If aged \<2 years at enrollment, has a documented historical MRI brain/cervical spine performed in the previous 12 months. * Have at least 6 months of available follow-up data after enrollment into the natural history study Exclusion Criteria: * Patients meeting any of the following criteria will not be included in the study: * Presence of severe obesity (BMI\>95% percentile on Hoover-Fong BMI charts); * Body weight \<7kg or \>30kg * History of chronic kidney disease (CKD) or …