1. Participants must be ≥ 3 years old, and < 10 years old (females) or < 11 years old (males),at the time of signing the informed consent form 2. A genetically confirmed diagnosis of Turner syndrome, SHOX deficiency or Noonan syndrome. 3. A height assessment corresponding to a height Z score of ≤ -2.00 SDs in reference to the general population of the same age and sex. 4. Tanner Stage 1, at time of signing the ICF. 5. Have been receiving continuous hGH for the treatment of short stature associated with their condition for a minimum of 1 year immediately prior to enrollment. 6. Are willing to continue on hGH for the Baseline Growth Phase, and for 2 years post randomization if randomized to the hGH arm. 7. Inadequate response to prior hGH treatment.

1. Participants with Turner syndrome known to have Y-chromosome material unless they have undergone gonadectomy and have fully external female genitalia.
2. Diagnosis of systemic disease or condition that may cause short stature other than Turner syndrome, SHOX deficiency, or Noonan syndrome, eg, renal, neoplastic, pulmonary, cardiac, gastrointestinal, immunologic and metabolic disease.
3. Bone age advanced beyond chronological age by more than 2 years.
4. Congenital heart disease which places the participant at increased risk of an adverse cardiac outcome in the setting of hypotension,
5. Have an unstable condition likely to require surgical intervention during the study.
6. 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 using bilateral lower extremity X-rays. 7. Previous limb-lengthening surgery, or planned or expected to have limb lengthening surgery during the study period. 8. Planned or expected bone-related surgery (ie, surgery involving disruption of bone cortex, excluding tooth extraction), during the study period