Gene Transfer Clinical Trial for Spinal Muscular Atrophy Type 1

Inclusion Criteria: * Six or nine months of age and younger (depending on cohort) on day of vector infusion with Type 1 SMA as defined by the following features: * Diagnosis of SMA based on gene mutation analysis with bi-allelic SMN1 mutations (deletion or point mutations) and 2 copies of SMN2. * Onset of disease at birth up to 6 months of age. * Hypotonia by clinical evaluation with delay in motor skills, poor head control, round shoulder posture and hypermobility of joints. Exclusion Criteria: * Active viral infection (includes HIV or serology positive for hepatitis B or C) * Use of invasive ventilatory support (tracheotomy with positive pressure)\* or pulse oximetry \<95% saturation. * Patients may be put on non-invasive ventilator support (BiPAP) for less than 16 hours a day at the discretion of their physician or research staff. * Concomitant illness that in the opinion of the PI creates unnecessary risks for gene transfer * Concomitant use of any of the following drugs: drugs for treatment of myopathy or neuropathy, agents used to treat diabetes mellitus, or ongoing immunosuppressive therapy or immunosuppressive therapy within 3 months of starting the trial (e.g. corticosteroids, cyclosporine, tacrolimus, methotrexate, cyclophosphamide, intravenous immunoglobulin, rituximab) * Patients with Anti-AAV9 antibody titers \>1:50 as determined by ELISA binding immunoassay. * Abnormal laboratory values considered clinically significant (GGT \> 3XULN, bilirubin ≥ 3.0 mg/dL , creatinine ≥ 1.8 mg/dL, Hgb \< 8 or \> 18 g/Dl; WBC \> 20,000 per cmm) Participation in a recent SMA treatment clinical trial that in the opinion of the PI creates unnecessary risks for gene transfer. * Family does not want to disclose patient's study participation with primary care physician and other medical providers. * Patient with signs of aspiration based on a swallowing test and unwilling to use an alternative method to oral feeding. * Patients with a single base substitution in SMN2 (c.859G\>C in exon 7) will be excluded based on predicted mild phenotype.