Interventional Study of Infigratinib in Children < 3 Years Old With Achondroplasia (ACH)

Inclusion Criteria:

* Diagnosis of ACH confirmed by genetic testing. If prospective participants had prior genetic testing, the diagnosis must be confirmed by a report from a certified laboratory, documenting the specific mutation.
* Age 0 to 32 months (2 years and 8 months) at screening.
* Signed informed consent, which must be obtained from each participant's parent(s) or legal guardian.
* Parent(s)/Guardian(s) willing and able to attend all study visits and comply with all study requirements.
* Parent(s)/Guardian(s) willing and able to comply with the routine care of the study participants according to local guidance for the management of infants and young children with ACH.
* Able to swallow age-appropriate oral medication.
* In participants \<1 year old, be compliant with recommended vitamin D supplementation of 5 10 μg/day or higher (or as recommended by country specific guidelines).

Exclusion Criteria:

* Participants who have hypochondroplasia or diagnosis of genetic condition other than ACH, or any clinical condition that can affect growth.
* Gestational age at birth \<37 weeks and/or birth weight \<2500 grams.
* Gastroesophageal reflux disease requiring prolonged treatment (\>1 week) with prohibited medications.
* Evidence of cervicomedullary compression, as defined by an Achondroplasia Foramen Magnum Score (AFMS) 4, symptomatic or asymptomatic, diagnosed during MRI done at screening or a previous MRI done at any time if the participant had not undergone decompression surgery.
* History of fracture of a long bone or spine within 6 months prior to screening.
* Any other significant concurrent disease or condition that, in the view of the investigator and/or sponsor, would confound assessment of efficacy or safety of infigratinib and/or would require treatment with a prohibited medication (per protocol), and/or would place the participant at high risk for poor treatment compliance or for failure to complete the study.
* Having received or planning to receive treatment with any other investigational or approved product for the treatment of ACH or short stature, including (but not limited to) r-hGH, IGF-1, CNP analog, FGF ligand trap, or treatment targeting FGFR inhibition at any time.
* Regular long-term (\>3 weeks; more than twice/year) treatment with supraphysiologic doses of glucocorticoid therapy (ie, \>15 mg/m2/day of hydrocortisone or equivalent) or treatment with glucocorticoids at anti-inflammatory doses (for over 3 weeks within 6 months of the screening visit. NOTE: Low-dose topical, inhaled, or intranasal corticosteroids are acceptable.
* Significant abnormality in screening laboratory results,
* Allergy or hypersensitivity to any components of the study drug.