This is a randomized, placebo-controlled study to investigate the safety, tolerability, pharmacokinetics and pharmacodynamics of single oral doses of Risdiplam in healthy Japanese participants.

Inclusion Criteria:

• Participants of Japanese origin, with Japanese parents (for the provisional Caucasian cohort, participants must be male or female Caucasians with 4 Caucasian grand-parents)
• Healthy participants. Healthy status is defined by the absence of evidence of any active or chronic disease following a detailed medical and surgical history, a complete physical examination including ophthalmological examination, vital signs, 12-lead electrocardiogram (ECG), hematology, blood chemistry, serology and urinalysis
• A body mass index (BMI) between 18 to 30 kilograms per square meter (kg/m^2) inclusive
• Male participants must agree to use a barrier method of contraception from dosing until completion of the study and for 4 months thereafter
• Female participants must be either surgically sterile or post-menopausal

Exclusion Criteria:

• Medical history of cardiovascular disease, renal disease, liver disease, digestive system disease, blood dyscrasia, immunologic disease, diseases of the nervous system, endocrine disease, metabolic disease, lung disease, or with anamnesis and obstacles in kidney, liver, or cardiopulmonary function
• Participants with any clinically significant eye pathology
• Laboratory test (hematology, biochemistry, physical examination or vital signs) values outside the institutional normal range and rated as clinically significant abnormal at screening
• Any clinically significant abnormalities in ECG at screening
• Inherited long QT syndrome or known family history of arrhythmia
• Systolic blood pressure (SBP) higher than 140 millimeters of mercury (mmHg) or below 90 mmHg, and/or diastolic blood pressure (DBP) higher than 90 mmHg or below 50 mmHg in the supine position, as assessed at screening
• Positive result for human immunodeficiency virus (HIV) antigen and antibody, hepatitis B surface antigen (HBsAg) or hepatitis C virus (HCV) antibody at screening
• Donation or loss of blood over 500 milliliters (mL) within three months prior to screening
• History of smoking more than 10 cigarettes a day. Participants who have quit smoking or who have reduced their daily cigarette smoking to 10 or less for more than one month prior to screening are allowed
• Daily consumption of food or drink containing a large amount of methylxanthine (caffeine, theophylline, theobromine)
• Present or past history of substance addiction, dependence or abuse, such as abuse of drugs or alcohol
• Concomitant or previous participation in any clinical trial either within 90 days or 5 half-lives of the investigational drug, whichever is longer, before administration of study drug in this study
• Use of prescribed medications which have systemic exposure within one week before enrolment
• Use of any concomitant drug during the study (including over-the-counter medication and medications used in dentistry)
• Inability to meet the study requirements in the opinion of the Investigator