A Study to Investigate the Pharmacokinetics and Safety of Risdiplam in Infants With Spinal Muscular Atrophy

Inclusion Criteria: * Male or female newborn infant aged \<20 days at first dose * Newborn infants with genetic diagnosis of 5q-autosomal recessive SMA or newborn infants identified as positive for SMA via newborn screening or via prenatal testing. * Gestational age equal to or greater than 37 weeks * Receiving adequate nutrition and hydration at the time of screening * Adequately recovered from any acute illness at baseline and considered well enough to participate in the study * Parent/caregiver is willing to consider nasogastric, nasojejunal, or gastrostomy tube placement during the study to maintain safe hydration, nutrition, and treatment delivery, if recommended by the investigator. Exclusion Criteria: * Presence of clinical symptoms or signs consistent with SMA Type 0 * In the opinion of the investigator, inadequate venous or capillary blood access for the study procedures * Systolic blood pressure or diastolic blood pressure or heart rate abnormalities * Presence of clinically relevant electrocardiogram (ECG) abnormalities * The infant (or the person breastfeeding the infant) taking any of the following: any inhibitor of CYP3A4 taken within 2 weeks (or within 5 times the elimination half-life, whichever is longer) prior to dosing, any inducer of CYP3A4 taken within 4 weeks (or within 5 times the elimination half-life, whichever is longer prior to dosing, and/or use of any multidrug and toxin extrusion (MATE) substrates taken within 2 weeks (or within 5 times the elimination half-life, whichever is longer) prior to dosing * Concurrent or previous administration of nusinersen or onasemnogene abeparvovec * Clinically significant abnormalities in laboratory test