, according to results of part 1 of the FIREFISH study.
A boost in SMN expression has been linked to improvements in survival and motor function, which was also observed in exploratory efficacy outcomes in the 2-part, phase 2-3, open-label study.
“No surviving infant was receiving permanent ventilation at month 12, and 7 of the 21 infants were able to sit without support, which is not expected in patients with type 1 spinal muscular atrophy, according to historical experience,” reported the FIREFISH Working Group led by Giovanni Baranello, MD, PhD, from the Dubowitz Neuromuscular Centre, National Institute for Health Research Great Ormond Street Hospital Biomedical Research Centre, Great Ormond Street Institute of Child Health University College London, and Great Ormond Street Hospital Trust, London.
However, “it cannot be stated with confidence that there was clinical benefit of the agent because the exploratory clinical endpoints were analyzed post hoc and can only be qualitatively compared with historical cohorts,” they added.
The findings were published online Feb. 24 in the New England Journal of Medicine.
A phase 2-3 open-label study
The study enrolled 21 infants with type 1 SMA, between the ages of 1 and 7 months. The majority (n = 17) were treated for 1 year with high-dose risdiplam, reaching 0.2 mg/kg of body weight per day by the twelfth month. Four infants in a low-dose cohort were treated with 0.08 mg/kg by the twelfth month. The medication was administered once daily orally in infants who were able to swallow, or by feeding tube for those who could not.
The primary outcomes of this first part of the study were safety, pharmacokinetics, pharmacodynamics (including the blood SMN protein concentration), and selection of the risdiplam dose for part 2 of the study. Exploratory outcomes included event-free survival, defined as being alive without tracheostomy or the use of permanent ventilation for 16 or more hours per day, and the ability to sit without support for at least 5 seconds.
In terms of safety, the study recorded 24 serious adverse events. “The most common serious adverse events were infections of the respiratory tract, and four infants died of respiratory complications; these findings are consistent with the neuromuscular respiratory failure that characterizes spinal muscular atrophy,” the authors reported. “The risdiplam-associated retinal toxic effects that had been previously observed in monkeys were not observed in the current study,” they added.
Regarding SMN protein levels, a median level of 2.1 times the baseline level was observed within 4 weeks after the initiation of treatment in the high-dose cohort, they reported. By 12 months, these median values had increased to 3.0 times and 1.9 times the baseline values in the low-dose and high-dose cohorts, respectively.
Looking at exploratory efficacy outcomes, 90% of infants survived without ventilatory support, and seven infants in the high-dose cohort were able to sit without support for at least 5 seconds. The higher dose of risdiplam (0.2 mg/kg per day) was selected for part 2 of the study.