PTC Therapeutics has reported results from Part 2 of the pivotal FIREFISH trial of Evrysdi (risdiplam), which demonstrated that infants with type 1 spinal muscular atrophy (SMA) continued to show improvements in survival and key motor milestones after two years of treatment.

A survival motor neuron 2 (SMN2)-directed RNA splicing modifier, Evrysdi can potentially treat SMA caused by mutations in chromosome 5q that lead to SMN protein deficiency.

The open-label, two-part pivotal trial in infants with Type 1 SMA had two parts. Part 1, a dose-escalation study, enrolled 21 infants with the primary objective of evaluating the safety profile of risdiplam and determining the dose for Part 2.

Part 2, a pivotal, single-arm study enrolled 41 infants with Type 1 SMA who were treated for two years and was followed by an open-label extension.

At 24 months of treatment, 93% of infants were alive and 83% were alive without permanent ventilation, results from Part 2 of the trial showed.

No new deaths were reported between 12 and 24 months and 92% of the infants receiving Evrysdi maintained the ability to feed orally at month 24.

As per the exploratory data, similar maintenance of 95% ability to swallow was noted.

Furthermore, hospitalisations reduced during the second year on treatment with Evrysdi compared with the natural course of the disease, with 34% of infants not needing hospitalisation during 24 months of treatment.

The study also met the primary endpoint of the percentage of infants able to sit without needing support for at least five seconds at 12 months.

PTC Therapeutics CEO Stuart Peltz said: “We’re encouraged to see these patients reach key motor and mobility milestones, which would never have been realised in the natural course of the disease.

“The long-term data presented today build upon the robust pool of evidence supporting Evrysdi as a safe, effective and convenient at-home treatment option for SMA patients globally.”

The US Food and Drug Administration recently approved Evrysdi for treating SMA in adults and children aged two months and above.

As part of a partnership with the SMA Foundation and PTC Therapeutics, the clinical development of Evrysdi is led by Roche.