Continuation Study of Long-term Safety, Tolerability, Pharmacokinetics and Efficacy of Recifercept in Achondroplasia

Inclusion Criteria: * Male and female participants between the ages of \>15 months to \<12 years inclusive, at Visit 1 (Screen 1). * Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests lifestyle considerations and other study procedures. * Completed the C4181005 Phase 2 study. * Able to stand independently for height measurements (if ≥2 years of age at enrollment). Exclusion Criteria: * Presence of co-morbid conditions or circumstances that, in the opinion of the investigator, would affect interpretation of growth data or ability to complete the trial procedures. * Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. * Presence of severe obesity (body mass index (BMI) \>95th percentile on Hoover-Fong BMI charts) \[Hoover-Fong et al, 2008\]. * Known closure of long bone growth plates (cessation of height growth). * Body weight \>45 kg. * History of hypersensitivity to study intervention or any excipients. * History of any prior treatment with human growth hormone or related products (including insulin-like growth factor 1 \[IGF-1\]). * History of receipt of any treatment that are known to potentially affect growth (including oral steroids \>5 days in the last 6 months, high dose inhaled corticoster…