Study 111-209 is a Phase 2 randomized, open-label clinical trial of BMN 111 in infants and young children with a diagnosis of Achondroplasia at a heightened risk of requiring cervicomedullary decompression surgery

Inclusion Criteria:

• Parent(s) or guardian(s) willing and able to provide signed informed consent after the nature of the study has been explained and prior to performance of any research related procedure.
• Have ACH, documented by genetic testing.
• Are willing and able to perform all study procedures as physically possible.
• Age 0 to ≤ 12 months, at study entry (Day 1). Given that any potential impact of vosoritide therapy on the foramen magnum is dependent on treating as early as possible and as long as possible while the synchondroses at the base of the skull are still open. For subjects > 6 months of age at enrollment, a discussion between the investigator and the Medical Monitor should occur with the goal of limiting the number of subjects in the range of > 6 months to ≤ 12 months of age.
• Parent(s) or caregiver(s) are willing to administer daily injections to the subject and complete the required training.
• Have evidence of CMC that "may" require surgical intervention

Exclusion Criteria:

• Have hypochondroplasia or short-stature condition other than achondroplasia (eg, trisomy 21, pseudoachondroplasia, etc).
• Have CMC that either does not require surgical intervention (for example foramen magnum narrowing with preservation of the cerebrospinal fluid space) or does require immediate surgical intervention .
• Have any of the following: Untreated congenital hypothyroidism or maternal history of hyperthyroidism, Insulin-requiring neonatal diabetes mellitus, Autoimmune inflammatory disease, Inflammatory bowel disease, Autonomic neuropathy.
• Have a history of any of the following:Renal insufficiency, Chronic anemia,Baseline systolic blood pressure below age and gender specified normal range or recurrent symptomatic hypotension (defined as episodes of low blood pressure generally accompanied by symptoms eg, pallor, cyanosis, irritability, poor feeding) and Cardiac or vascular disease.
• Have a clinically significant finding or arrhythmia that indicates abnormal cardiac function or conduction or QTc-F ≥ 450 msec on screening ECG.
• Have been treated with growth hormone, insulin-like growth factor 1, or anabolic steroids in the 6 months prior to Screening, or long-term treatment (> 3 months) at any time.
• Have ever had prior cervicomedullary decompression surgery.
• Have had a fracture of the long bones or spine within 6 months prior to Screening.