Investigate Safety, Tolerability, PK, PD and Efficacy of Risdiplam (RO7034067) in Infants With Type1 Spinal Muscular Atrophy

Inclusion Criteria: * Clinical history, signs or symptoms attributable to Type 1 SMA with onset after 28 days but prior to the age of 3 months * Gestational age of 37 to 42 weeks * Confirmed diagnosis of 5q-autosomal recessive SMA * Participants has two survival motor neuron 2 (SMN2) gene copies, as confirmed by central testing * Body weight greater than or equal to (\>=) third percentile for age, using appropriate country-specific guidelines * Receiving adequate nutrition and hydration (with or without gastrostomy) at the time of screening, in the opinion of the Investigator * Adequately recovered from any acute illness at the time of screening and considered well-enough to participate in the opinion of the Investigator Exclusion Criteria: * Concomitant or previous participation in any investigational drug or device study within 90 days prior to screening or 5 half-lives, whichever is longer * Concomitant or previous administration of SMN2-targeting antisense oligonucleotide, SMN2 splicing modifier or gene therapy study * Any history of cell therapy * Hospitalization for pulmonary event within the last 2 months, or planned at the time of screening * Presence of clinically relevant electrocardiogram (ECG) abnormalities before study drug administration * Unstable gastrointestinal, renal, hepatic, endocrine or cardiovascular system diseases * Participants requiring invasive ventilation or tracheostomy * Participants requiring awake non-invasive ventilation or with awake hypo…