A Study of GDC-0134 to Determine Initial Safety, Tolerability, and Pharmacokinetic Parameters in Participants With Amyotrophic Lateral Sclerosis

Inclusion Criteria: * Male or female participants with a diagnosis of possible, laboratory-supported probable, probable, or definite ALS according to modified El Escorial criteria * Upright forced vital capacity of at least 50 percent (%) * Ability to fast from food for 8 hours prior to dosing and 2 hours after dosing Exclusion Criteria: * Currently taking riluzole unless on a stable dose for the 3 months prior to Day -1 and without current liver enzyme or liver function abnormalities * Currently taking edaravone unless after completion of at least the second 14-day drug-treatment period, as long as Day 1 occurs during a drug-free period at least 24 hours after the last edaravone dose and at least 5 days prior to the first dose of the next cycle * Positive for hepatitis C antibody, hepatitis B surface antigen, or human immunodeficiency virus (HIV) antibody * Clinically significant thrombocytopenia * Currently taking nutritional/herbal supplements, except for over-the-counter vitamins that are within Recommended Dietary Allowance (RDA), unless discontinued at least 7 days prior to Day -1, except upon approval of both the investigator and Sponsor * For participants participating in a designated drug-drug interaction (DDI) cohort in the MAD stage of the study, who require midazolam/caffeine administration: known allergy, religious prohibition, or other condition limiting midazolam or caffeine administration