Study of Infigratinib in Children With Achondroplasia

Inclusion Criteria: 1. Signed informed consent by participant or parent(s) or legally authorized representative (LAR) and signed informed assent by the participant (when applicable). 2. Diagnosis of ACH, documented clinically and confirmed by genetic testing. 3. At least a 6-month period of growth assessment in the PROPEL study (Protocol QBGJ398-001) before study entry. 4. Ambulatory and able to stand without assistance 5. Able to swallow oral medication. Exclusion Criteria: 1. Hypochondroplasia or short stature condition other than ACH. 2. In females, having had their menarche. 3. Height \< -2 or \> +2 standard deviations for age and sex based on reference tables on growth in children with ACH. 4. Significant concurrent disease or condition that, in the view of the Investigator and/or Sponsor, would confound assessment of efficacy or safety of infigratinib. 5. Current evidence of corneal or retinal disorder/keratopathy. 6. History of malignancy. 7. Currently receiving treatment with agents that are known strong inducers or inhibitors of CYP3A4 and medications which increase serum phosphorus and/or calcium concentration. 8. Treatment with growth hormone, insulin-like growth factor 1 (IGF-1), or anabolic steroids in the previous 6 months or long-term treatment (\>3 months) at any time. 9. Treatment with a C-type natriuretic peptide (CNP) analog, fibroblast growth factor (FGF) ligand trap, or treatment targeting FGFR inhibition at any time. 10. Regular long-term treatment (\>3 weeks) with oral corticosteroids (low-dose ongoing inhaled steroid for asthma is acceptable). 11. Treatment with any other investigational product or investigational medical device for the treatment of ACH or short stature. 12. Previous limb-lengthening surgery or guided growth surgery. 13. Fracture within 12 months of screening.