An Open Label Study of LMI070 (Branaplam) in Type 1 Spinal Muscular Atrophy (SMA)

Inclusion Criteria: Common for both Parts 1 and 2: * Type 1 SMA, diagnosed clinically, with symptom onset \<6 months of age and genetic confirmation of mutations in both alleles of the SMN1 gene, and with SMN2 copy number of 2. * Best supportive care in place and stable for at least 14 days before screening. * Must be able to demonstrate antigravity strength in both biceps. At birth gestational age \>32 weeks and body weight at birth \>2 kg. * Must live within 2 hours drive of study center. Clearance should be obtained from the site investigator and sponsor if the patient resides more than 2 hours ground travel from the study center Specific for Part 1 * Age at screening between 1 and 7 months * Must have or agree to have placement of feeding tube for enteral access via nasogastric (NG), nasojejunal (NJ), percutaneous gastrostomy (PEG), or percutaneous jejunostomy (PEJ) tube for administration of branaplam (for patients in whom branaplam cannot be administered orally ; NG tube may be removed between doses). Specific for Part 2 * Age at screening between 30 and 180 days of age * Must have or agree to have placement of feeding tube for enteral access via nasogastric (NG), nasojejunal (NJ), percutaneous gastrostomy (PEG), or percutaneous jejunostomy (PEJ) tube for administration of branaplam (for the first administration only and for patients in whom branaplam cannot be administered orally; NG tube may be removed between doses). * Minimum CHOP INTEND score of 15 at baselin…