A Study to Investigate the Efficacy and Safety of RO5285119 in Participants With Autism Spectrum Disorder (ASD)

• Fluent in English
• Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria for ASD or International Statistical Classification of Diseases and Related Health Problems, 10th revision (ICD10) criteria for Autism diagnosis confirmed by Autism Diagnostic Observational Schedule (ADOS-2) criteria
• Social Responsiveness Scale, second edition (SRS-2) (T-score) >= 66
• Clinical Global Impressions of Severity (CGI-S) >= 4 (moderately ill) at screening
• IQ >= 70 as assessed by Wechsler Abbreviated Scale of Intelligence Scale: Second Edition (WASI-II) or Wechsler Preschool and Primary Scale of Intelligence: Fourth Edition (WPPSI-IV) intelligence test
• Language, hearing, and vision compatible with the study measurements as judged by the investigator

Inclusion Criteria for the OLE:

• Have completed the blinded treatment phase of the study OR were required to stop dosing at or before Week 8
• Have no adverse events that would prohibit starting the OLE

• Initiation of a major change in psychosocial intervention (including investigational) within 4 weeks prior to screening
• Unstable or uncontrolled clinically significant psychiatric and/or neurological disorder that may interfere with the safety or efficacy endpoints
• Known personal or family history of cerebral aneurysm
• Risk of suicidal behavior
• Seizure within the past 6 months
• Medical history of alcohol or substance abuse/dependence
• Concurrent cardio-vascular disease not considered well controlled by the Investigator
• Clinically significant abnormality on electrocardiogram at screening
• Concomitant disease or condition (pulmonary, gastro-intestinal, hepatic, renal, metabolic, immunological system, or obesity that could interfere with the conduct of the study
• Evidence for current gastro-intestinal bleeding, e.g., active stomach ulcer disease
• History of coagulopathies, bleeding disorders, or blood dyscrasias
• Positive serology for hepatitis B (HBV), hepatitis C (HCV), human immunodeficiency virus (HIV) 1, or HIV 2
• Confirmed clinically significant abnormality in parameters of hematology, clinical chemistry, coagulation, or urinalysis
• Medical history of malignancy if not considered cured
• Participation in an investigational drug study within 90 days or 5 times the half-life of the investigational molecule (whichever is longer) prior to randomization
• Loss of blood over 250 milliliters within three months prior to screening
• Allowed medications have not been stable since 4 weeks before screening, and allowed medications for treatment of epilepsy have not been stable since 3 months before screening
• Use of prohibited medications within 2 weeks prior to screening visit or 5 times the half-life prior to randomization (whichever is longer)