A Clinical Trial to Evaluate Efficacy and Safety of TransCon CNP Compared With Placebo in Infants (0 to <2 Years of Age) With Achondroplasia

Inclusion Criteria:

• Written, signed informed consent by the parent(s)/caregiver(s) of the participant,and as required by the institutional review board/human research ethicscommittee/independent ethics committee (IRB/HREC/IEC).

• Male or female younger than 2 years of age at the time of randomization; or for openlabel sentinel participants, at the time of first administration of IMP.

• Clinical diagnosis of achondroplasia (ACH) with genetic confirmation of heterozygousgenotype present during screening.

• Parent(s)/caregiver(s) willing to follow the protocol and instructions provided,including being able to administer weekly subcutaneous injections of trialtreatment.

• Compliance to daily Vitamin D supplementation for infants aged 14 days to 1 year.All participants older than 1 year of age with serum 25-hydroxyvitamin D (25OHD)measured below lower limit of reference range at screening should start dailyVitamin D supplementation prior to randomization.

• Considered eligible based on the medical history, physical examination, and theresults of vital signs, ECG, imaging, and clinical laboratory tests performed duringthe screening period.

Exclusion Criteria:

• Known or suspected hypersensitivity to the investigational product or relatedproducts (trehalose, tris[hydroxymethyl]aminomethane, succinate, and polyethyleneglycol [PEG]).

• Genetic confirmation of ACH homozygous genotype.

• Premature birth with gestational age < 32 weeks.

• Premature birth with gestational age 32 to 37 weeks, unless time from birth is > 6months at the time of screening and the child is in good nutritional status, definedas gain in body weight expected for age and diagnosis of ACH, as determined by theInvestigator and confirmed with the Medical Monitor.

• Anticipated, as assessed by Investigator and confirmed with Medical Monitor, toundergo surgical intervention during trial participation, including cervicomedullarydecompression. Evaluation of immediate risk of requiring cervicomedullarydecompression surgery will rely on the following assessments:

• Physical examination (e.g., neurologic findings of clonus, opisthotonus,exaggerated reflexes, dilated facial veins)

• Evidence of uncontrolled sleep apnea as confirmed by local standard of careassessment (e.g. polysomnography or simple sleep test) performed within 6months prior to screening.

• MRI performed at screening indicating presence of severe cervicomedullarycompression (CMC) or spinal cord damage. Presence of abnormal MRI T2 signalintensity at and immediately above and below the cervicomedullary junctionshould be considered high risk for requiring surgery and the participant is noteligible for trial participation.

Common surgeries, such as insertion of grommets, adenoidectomy, tonsillectomy, or myringotomy tube placement are permitted during trial participation.

• Have a growth disorder or medical condition, other than ACH, resulting in shortstature or abnormal growth as determined by the Investigator and confirmed with theMedical Monitor.

• Have received any dose of prescription medications and/or investigational medicinalproduct or device intended to affect stature, growth, or body proportionality (including human growth hormone or vosoritide) at any time.

• Requires or anticipated to require chronic (> 4 weeks) or repeated treatment (morethan twice/year) with oral corticosteroids, or high-dose inhaled corticosteroidsduring trial participation.

• History or presence of injury or disease of the growth plate(s), other than ACH,affecting growth potential of long bones, including Salter-Harris fracture andrecent bone-related surgery, as determined by Investigator and confirmed with theMedical Monitor.

• Have a clinically significant finding indicating abnormal cardiac function,including but not limited 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.

• QTcF ≥ 450 msec on screening 12-lead ECG.

• History or presence of a condition impacting hemodynamic stability (such asautonomic dysfunction and orthostatic intolerance).

• History or presence of the following:

• Chronic anemia.

• Chronic renal insufficiency.

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

• History or presence of malignant disease.

• Any disease or condition that, in the opinion of the Investigator, may make theparticipant unlikely to fully complete the trial, not adhering to trial procedures,may confound interpretation of trial results, or may present undue risk fromreceiving trial treatment. This could include family situations, comorbidconditions, or medications that might impact safety or be considered confounding.