Shares of PTC Therapeutics Inc. (PTCT) - Get Report soared in premarket trading on Monday, June 18, after the biotech firm over the weekend presented updated interim clinical data on spinal muscular atrophy (SMA) drug risdiplam.

The stock jumped 33.2% to $50 ahead of the opening bell.

The data, presented on Saturday at the 22nd Annual SMA Researcher Meeting, showed that at Day 182, more than 90% of babies had an increase of more than four points in their Chop-Intend score compared to the baseline. The Chop-Intend is an assessment of motor skill in SMA Type 1.

South Plainfield, N.J.-based PTC is collaborating with Roche Holdings AG and the SMA Foundation on the program.

The data prompted RBC Capital Markets LLC analyst Brian Abrahams to upgrade his rating on the stock.

"Following impressive data for oral SMA drug RG7916 at CureSMA over the weekend, we are upgrading PTCT to Outperform from Sector Perform," Abrahams wrote in a Monday note.

The updated interim data presented were from the first part of a study, dubbed Firefish, of risdiplam in babies with Type 1 SMA. The second part of the study is ongoing.