SMA is a rapidly progressing neurologic disease caused by biallelic SMN1 deletion/mutation. Copies of a similar gene (SMN2) modify disease severity. Early diagnosis is critical, as infants treated early see greater improvements in motor function.

As of 31 May 2019, 23 infants were dosed (8–43 days of age [mean: 24.7]; 2xSMN2, n=10; 3xSMN2, n=12; 4xSMN2, n=1). All patients are alive and no patient in SPR1NT required ventilation support at last visit. Among 2xSMN2 patients, 7 achieved a full/near full CHOP INTEND score of 60–64 by 3 months; 6 have achieved sitting (within the WHO sitting age range [1st–99th percentile]: 3.8–9.2 months); no child >9.1 months failed to sit. Among 3xSMN2 patients, 2 sat and 1 crawled and stood with assistance. All patients (2x–3xSMN2) with a 6-month swallow evaluation (12/12) had normal swallowing and fed exclusively by mouth. As of 8 March 2019, treatment-emergent adverse events of special interest were reported in 4 patients.

Preliminary SPR1NT data show no ventilatory support, age-appropriate motor development, and intact swallowing in presymptomatic SMA patients dosed one-time with onasemnogene abeparvovec, underscoring the importance of early treatment.