The purpose of this study is to evaluate the long-term safety and efficacy of daily doses of vosoritide in participants with HCH

Inclusion Criteria:

• Participants must have completed the Week 52 visit for 111-303 or 111-212 and have open epiphyses as assessed by left hand antero-posterior (AP) X-rays
• Parent(s) or guardian(s) must be willing and able to provide written, signed informed consent after the nature of the study has been explained and prior to performance of any study-related procedure
• Females ≥ 10 years old or who have begun menses must have a negative pregnancy test at the Baseline visit and be willing to have additional pregnancy tests during the study
• If sexually active, participants must be willing to use a highly effective method of contraception while participating in the study
• Participants are willing and able to perform all study procedures as physically possible
• Parent(s) or caregiver(s) are willing to administer daily injections to the participants and willing to complete the required training

Exclusion Criteria:

• Permanently discontinued study treatment in the studies 111-303 or 111-212
• Evidence of decreased growth velocity (AGV < 1.5 cm/year) as assessed over a period of at least 6 months and growth plate closure assessed as per standard of care
• Taking or planning to take any prohibited medications
• Planned or expected to have limb-lengthening surgery during the study period
• Planned or expected bone-related surgery during the study period
• Require any investigational agent prior to completion of study period
• Have current malignancy, history of malignancy, or currently under work-up for suspected malignancy
• Have known hypersensitivity to vosoritide or its excipients
• Is pregnant or breastfeeding at Baseline or planning to become pregnant (self or partner) at any time during the study
• Concurrent disease or condition that, in the view of the investigator, would interfere with study participation or safety evaluations, for any reason