Inclusion Criteria:  Children between 2 and 12 years of age Open epiphyses on bone age x ray Must be on stable medication and psychosocial treatment regimens for at least three months prior to enrollment, assuming the concomitant medication is safe for use with Growth Hormone No prior use of Growth Hormone or IGF-1 ASD group: Meet DSM-5 criteria for Autism Spectrum Disorder confirmed by the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2); absence of known pathogenic copy number variants PMS group: Known pathogenic deletions or mutations in SHANK3 gene diagnosed by array CGH and/or direct sequencing  Exclusion Criteria:  Closed epiphyses Active or suspected neoplasia Intracranial hypertension Hepatic insufficiency Renal insufficiency Cardiomegaly/valvulopathy History of allergy to growth hormone or any component of the formulation (mecasermin) Patients with comorbid conditions who are deemed too medically compromised to tolerate the risk of experimental treatment with growth hormone (including severe obesity, sleep apnea, and various acute health conditions) Visual problems that preclude the use of VEP