A Study of TYRA-300 in Children With Achondroplasia: BEACH301

The purpose of this study is to evaluate the safety, tolerability, and identify potentially effective dose(s) of TYRA-300 in children with achondroplasia with open growth plates.

Inclusion Criteria: * Aged 3 to 10 years old (inclusive) at the time of consent. * Informed consent provided by parent(s) or legal guardian(s). As study participants are less than 18 years old, participants are willing and able to provide written assent (where applicable and required). * Molecular diagnosis of achondroplasia (FGFR3 G380R). * Radiographically confirmed open growth plates at Screening, as determined by bone age X-ray. * Able to stand and ambulate independently. * Able to take oral medication. * Sentinel Safety Cohort only: aged 5 to 10 years old (inclusive). * Cohort 1 only: aged 3 to 10 years old (inclusive) and are naive to prior growth accelerating therapy. * Cohort 2 only: aged 3 to 10 years old (inclusive) and have received prior growth accelerating therapy. Exclusion Criteria: * Presence or history of any concurrent disease or condition that would interfere with study participation, safety evaluations, or any uncontrolled or untreated condition that could impact pediatric growth. * Diagnosis of endocrine condition that alters calcium/phosphate homeostasis. * Prior limb lengthening surgery or planned or expected to have limb lengthening surgery while enrolled in the study. * Taking medications that are strong inhibitors or inducers of cytochrome P450 (Cyp) 3A4. * History or current evidence of corneal or retinal disorder/keratopathy. * Presence of guided growth hardware/8 plates. Planned or anticipated orthopedic surgeries.