The purpose of this study is to evaluate the safety and efficacy of daily administration of vosoritide in participants with HCH aged 0 to < 36 months over a 52-week period.

Study 111-212 is a Phase 2, randomized, double-blind, placebo-controlled, multicenter study to assess the safety and efficacy of vosoritide versus placebo in infants and young children with HCH.

Eligible participants with documented HCH confirmed by genetic testing will be randomized in a 1:1 ratio to receive vosoritide or placebo. Participants will receive study treatment daily for 52 weeks by subcutaneous (SC) injection, followed by a 2-week safety follow-up visit. Vosoritide dosing will follow a weight-band regimen.

Key Inclusion Criteria:

1. Participants must be 0 to < 36 months of age at randomization.
2. Participants must have a confirmed genetic diagnosis of HCH (obtained via whole genome sequencing; presence of a FGFR3 pathogenic variant associated with HCH).
3. Participants aged 0 to < 12 months must have a height Z-score of ≤ -1.0 SDS andparticipants aged ≥ 12 to < 36 months must have a height Z-score of ≤ -2.0 SDS in reference to the average stature of the same sex and age, as calculated using the Center for Disease Control and Prevention (CDC) growth charts.
4. Participant's weight at the Day 1 visit (pre-treatment) must be ≥ 3 kg.

Key Exclusion Criteria:

1. Short stature condition other than HCH (eg, ACH, trisomy 21, pseudoachondroplasia).
2. Have an unstable medical condition likely to require surgical intervention during the study period.
3. Taking any of the prohibited medications.
4. Have been treated with growth hormone, insulin-like growth factor 1 (IGF-1), or anabolic steroids in the 6 months prior to Screening, or long-term treatment (> 3 months) at any time.
5. Require any investigational agent prior to completion of study period.
6. Have received another investigational product or investigational medical device within 30 days prior to the Screening visit.
7. Have used any other investigational product or investigational medical device for the treatment of HCH or short stature at any time.
8. Have current malignancy, history of malignancy, or currently under work-up for suspected malignancy.
9. Have known hypersensitivity to vosoritide or its excipients.
10. Have a condition or circumstance that, in the view of the investigator, places the participant at high risk for poor treatment compliance or for not completing the study.
11. Have any concurrent disease or condition that, in the view of the investigator, will interfere with study participation or safety evaluations, for any reason.