Background: SMA is a neurodegenerative disease caused by biallelic deletion/mutation of SMN1. Copies of a similar gene (SMN2) modify disease severity. In a phase 1 study, SMN GRT onasemnogene abeparvovec (AVXS-101) improved outcomes of symptomatic SMA patients with two SMN2 copies (2xSMN2) dosed ≤6 months. Because motor neuron loss can be insidious and disease progression is rapid, early intervention is critical. This study evaluates AVXS-101 in presymptomatic SMA newborns. Methods: SPR1NT is a multicenter, open-label, phase 3 study enrolling ≥27 SMA patients with 2–3xSMN2. Asymptomatic infants ≤6 weeks receive a one-time intravenous AVXS-101 infusion (1.1x1014 vg/kg). Safety and efficacy are assessed through study end (18 [2xSMN2] or 24 months [3xSMN2]). Primary outcomes: independent sitting for ≥30 seconds (18 months [2xSMN2]) or assisted standing (24 months [3xSMN2]). Results: From April–September 2018, 7 infants received AVXS-101 (4 female; 6 with 2xSMN2) at ages 8–37 days. Mean baseline CHOP-INTEND score was 41.7 (n=6), which increased by 6.8, 11.0, 18.0, and 22.5 points at day 14 (n=4), month 1 (n=3), 2 (n=3), and 3 (n=2). Updated data available at the time of the congress will be presented. Conclusions: Preliminary data from SPR1NT show rapid motor function improvements in presymptomatic SMA patients.