A Study to Assess the Effects of RO6889450 (Ralmitaront) in Participants With Schizophrenia or Schizoaffective Disorder and Negative Symptoms

Inclusion Criteria: * Patients with a Diagnostic and Statistical Manual of Mental Disorders (DSM-5) diagnosis of schizophrenia or schizoaffective disorder as confirmed by the Mini International Neuropsychiatric Interview (MINI) * Part B only: Stable treatment with a dopamine/serotonin (D2/5HT2A) antagonist or pure D2 antagonist(s), or a D2 partial agonist for a minimum of 6 months and receiving no more than two antipsychotics * Medically stable during the 3 months prior to study entry * Participant is an outpatient with no psychiatric hospitalizations within the prior 6 months * PANSS negative symptom factor score of 18 or higher * The following rating on items of the PANSS: (a) less than 5 on G8 (uncooperativeness), P1 (delusions), P3 (hallucinations), P4 (excitement/hyperactivity), and P6 (suspiciousness/persecution); (b) less than 4 on P7 (hostility), and G14 (poor impulse control) * Has an informant who is considered reliable by the Investigator * Body mass index (BMI) between 18-40 kg/m2 inclusive * Female participants are eligible to participate if not pregnant, not breastfeeding and agree to remain abstinent or use acceptable contraceptive methods during the treatment period and for at least 28 days after the last dose of study drug Exclusion Criteria: * Moderate to severe substance use disorder within six months of study entry (excluding nicotine or caffeine) as defined by DSM-5 * Extrapyramidal symptom rating scale (ESRS-A CGI) subscore greater than or equal to 3 …