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

Who May Qualify: - 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. Who Should NOT Join This Trial: - 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 Always talk to your doctor about whether this trial is right for you.