A Clinical Trial to Evaluate Efficacy and Safety of Navepegritide in Adolescents (12 - 18 Years of Age) With Achondroplasia.

Inclusion Criteria:

• Written, signed informed consent and/or assent of the participant, participantparent(s) or legal guardian(s) of the participant, and as required by theinstitutional review board/human research ethics committee/independent ethicscommittee (IRB/HREC/IEC). For participants who are below the age of consent, awritten assent will be obtained in accordance with applicable requirements asrequired by IRB/HREC/IEC. Upon reaching the legal age of consent, depending onapplicable requirements, these participants will be asked to give their own writtenconsent.

• Male or female, between 12 (inclusive) and 18 years of age at the time ofrandomization

• Clinical diagnosis of ACH with documented genetic confirmation available.Documentation of historic test results are acceptable for proof of diagnosis.

• Parent(s)/legal guardian(s) willing and able to administer weekly SC injections ofIMP and to follow the protocol.

• At least one historical standing height measurement available from medical records.The measurement must have been collected between 6 months to 15 months prior to thetime of screening.

Exclusion Criteria:

• Participation (signed informed consent) in any interventional clinical trial within 3 months prior to Screening unless no doses of IMP was given.

• Decreased growth velocity (AGV less than 1.5 cm/year based on measurement over aperiod of at least 6 months) or radiological evidence of growth plate closure.

• Known or suspected hypersensitivity to the IMP or related products (trehalose,tris[hydroxymethyl]aminomethane, succinate, and mPEG).

• Have a growth disorder or medical condition other than ACH that results in shortstature, or abnormal growth such as SADDAN, hypochondroplasia, growth hormonedeficiency, Turner syndrome, pseudo-ACH, inflammatory bowel disease, celiac disease,hypothyroidism, hyperthyroidism, or diabetes mellitus.

• Severe mutation in the FGFR3 gene, e.g. two variants on the same allele or severeACH with developmental delay and acanthosis nigricans, are not eligible for trialparticipation.

• Have received any dose of prescription medications and/or IMP (placebo treatmentonly is allowed, if documented) or surgical intervention intended to affect stature,growth, or body proportionality at any time.

• Requires, or anticipated to require, chronic (more than 4 weeks) or repeatedtreatment (more than twice/year and less than 3 weeks/year) with systemiccorticosteroids during participation in the trial. Chronic use of high dose inhaledcorticosteroids is not allowed.

• Known history of presence of injury or disease of the growth plate(s), other thanACH, that affects growth potential of long bones.

• Known history of any bone-related surgery affecting growth potential of long bones,such as:

• Orthopedic reconstructive surgery for bone lengthening (e.g., procedures forleg bowing such as 8-plate are not exclusionary).

• Ventriculoperitoneal (VP) shunt and laminectomy with full recovery are allowedwith minimum of 6 months of bone healing.

• Bone fracture within 6 months prior to screening (within 2 months for fractureof digits and buckle fractures).

• Clinically significant findings at Screening, such as:

• Expected to require surgical intervention during participation in the trialthat may significantly affect trial parameters (confounding of safety events)or would prevent the participant from performing trial procedures. Commonsurgeries, such as insertion of grommets, adenoidectomy, tonsillectomy, ormyringotomy tube placement, are permitted.

• Severe untreated sleep apnea or newly initiated sleep apnea treatment (e.g.,Continuous Positive Airway Pressure [CPAP] in the previous 2 months prior toScreening.

• MS disease, such as Salter-Harris fractures or clinical and/or radiographicevidence of severe hip pathology

• Otherwise, are considered by the Investigator to be unfit to receive trialtreatment or undergo trial related procedures.

• Have a clinically significant finding or arrhythmia as determined by theinvestigator in consultation with the medical monitor that indicates abnormalcardiac function or conduction that includes, but is not exclusive to:

• Repaired or unrepaired coarctation.

• Moderate or greater complexity congenital heart disease including tetralogy ofFallot, Atrioventricular septal defects, truncus arteriosus, total anomalouspulmonary venous return, double outlet right ventricle, or single ventricleheart disease.

• QT corrected using Fridericia's correction (QTcF) ≥ 450 msec at Screening.

• Known history or presence of condition that impacts hemodynamic stability (such asautonomic dysfunction and orthostatic intolerance).

• Known history or presence of the following:

• Chronic anemia (iron deficiency anemia that is resolved or adequately treatedin the Investigator's opinion is allowed).

• Chronic renal insufficiency defined as estimated glomerular filtration rate (eGFR) according to the revised bedside Schwartz equation less than 60mL/min/1.73 m2 for more than 3 months.

• Chronic or recurrent illness that can affect hydration or volume status,including conditions associated with decreased nutritional intake or increasedvolume loss.

• Known history or presence of malignant disease.

• Participant with serum 25-hydroxy-vitamin D (25OHD) levels of less than 30 nmol/L (less than 12 ng/mL) at Screening Visit will be excluded. Participants with 25OHDlevels between 30-50 nmol/L (12-20 ng/mL) can be randomized provided treatment withVitamin D supplementation is initiated according to local standards.

• Any disease or condition that, in the opinion of the Investigator, may make theparticipant unlikely to fully complete the trial, may confound interpretation oftrial results, or may present undue risk from receiving trial treatment. This couldinclude family situations, complications or manifestations, or medications thatmight impact safety or be considered confounding.

• Sexually active male and female participants and female partners of maleparticipants of childbearing potential not using a highly effective form ofcontraceptive for the entire trial period and for 90 days after last dose of trialtreatment.

• Female participants who are pregnant, lactating or breastfeeding.