An Interventional Study of Infigratinib in Children With Hypochondroplasia

Key Inclusion Criteria: * Participants must have completed at least 26 weeks and still be on the observational study (QBGJ398-004). * Phase 2 portion: Participants 5-11 years of age (inclusive). * Phase 3 portion: Participants 3 to \<18 years of age at screening with growth potential * Diagnosis of HCH documented clinically by the presence of disproportionate short stature and confirmed with a molecular test. * Participants are able to swallow oral medication. * Participants and parent(s), legal guardian(s), or caregiver(s) are willing and able to comply with study visits and study procedures. * Participants are ambulatory and able to stand without assistance. Sex and Contraceptive/Barrier Requirements * Negative pregnancy test in girls ≥10 years of age or girls of any age who have experienced menarche. * If sexually active, participants whether male or female, must be willing to use a highly effective method of contraception, as relevant, while taking study drug and for 1 month after the last dose of study drug. * Signed informed consent. Key Exclusion Criteria: * Participants who have ACH or a short stature condition other than HCH. * Significant concurrent disease or condition that, in the view of the investigator and/or sponsor, would confound assessment of efficacy or safety of infigratinib. * Current evidence of clinically significant corneal or retinal disorder/keratopathy confirmed by ophthalmic examination. * Concurrent circumstance, disease, or condition that, in the view of the investigator and/or sponsor, would interfere with study participation or safety evaluations. * History and/or current evidence of extensive ectopic tissue calcification. * History of malignancy. * Having received or planning to receive treatment with any other investigational or approved product for the treatment of ACH, HCH, or short stature. * Regular long-term treatment (≥3 weeks) with supraphysiologic doses of glucocorticoid. * Previous limb-lengthening surgery at any time or planned/expected to have limb-lengthening or guided growth surgery while participating in the study. * Participants receiving medications which could increase serum phosphorus and/or calcium concentrations * Clinically significant abnormality in any laboratory test result at screening. * Pregnant or breastfeeding at the screening visit or planning to become pregnant (self or partner) at any time during the study. * Allergy to any components of the study drug. * Concurrent circumstance, disease, or condition that would interfere with study participation.