Confirmatory Part 2 of FIREFISH Demonstrates Survival and Motor Milestones Not Seen in Natural History in Infants with Type 1 Spinal Muscular Atrophy

- Part 2 of pivotal study met its primary endpoint by demonstrating unsupported sitting in infants aged 1-7 months with type 1 SMA after 12 months of treatment -

- Meaningful benefit observed in dose-finding Part 1 confirmed -

- PDUFA expected August 24, 2020 -

SOUTH PLAINFIELD, N.J., April 28, 2020 /PRNewswire/ -- PTC Therapeutics, Inc. (NASDAQ: PTCT) today announced positive results from part 2 of the pivotal FIREFISH study evaluating risdiplam in infants with type 1 spinal muscular atrophy (SMA). The global study met its primary endpoint of infants sitting without support for five seconds by month 12, as assessed by the Gross Motor Scale of the Bayley Scales of Infant and Toddler Development Third Edition (BSID-III). Type 1 SMA babies do not achieve this milestone without therapy. Substantial results were demonstrated across multiple secondary and exploratory endpoints, as infants in the study achieved milestones not seen in natural history. In addition to being able to sit without support, infants were able to maintain upright head control, roll to the side, and stand without support after 12 months of treatment. At 12 months, 95% infants maintained the ability to swallow and 89% were able to feed orally. No new safety signals were identified in part 2 of the study. These data will be reviewed during a conference call today at 11:30 am ET by our development partner, Roche.

"The positive results from part 2 of the FIREFISH study reinforce the clinically meaningful efficacy seen in part 1 of the trial and support its overall safety profile," said Stuart W. Peltz, Ph.D., Chief Executive Officer of PTC Therapeutics. "This is even more impressive since this study included many patients whose disease had already progressed significantly before starting treatment. We expect that risdiplam will be the most competitive global product for a broad range of SMA patients and are confident in Roche's ability to conduct a robust launch following approval. A significant unmet need exists within the SMA population, particularly for an oral, at home therapy in the current environment."

The single-arm part 2 of FIREFISH assessed the efficacy of risdiplam in 41 infants (eligible age at enrollment between 1 and 7 months) with type 1 SMA treated for 12 months. The study met its primary endpoint with 29% of infants (12/41; p