A Phase 1 Trial of Riluzole in Spinal Muscular Atrophy

Background: Severe spinal muscular atrophy (SMA) (Werdnig-Hoffmann disease, acute SMA, and SMA I) is a disease of the motor neuron characterized by onset before 6 months of age, failure ever to achieve sitting without support, and a life expectancy of 2 years or less. There is no known treatment for SMA, and, until recently, no therapeutic trials have been attempted. There is reason to believe that glutamate, an excitatory neurotransmitter, enhances programmed cell death of anterior horn cells. Riluzole, a glutamate inhibitor, has been shown to slow the rate of decline in patients with amyotrophic lateral sclerosis, another form of motor neuron disease. Objectives: To determine whether a glutamate inhibitor might be tolerated by infants with SMA and, furthermore, whether this medication could have a positive effect on life expectancy. Design: Subjects with homozygous deletions of the survival motor neuron gene were recruited from pediatric neuromuscular clinics and randomized in a 2:1 ratio, 2 riluzole to 1 placebo. Neurologic examination was performed at the first visit by one of the investigators. Complete blood count, hepatic and renal screens, and urinalysis were performed at baseline, 2 weeks, 1 month, 2 months, 3 months, 6 months, and 9 months after drug or placebo was started. An electrocardiogram was done at baseline, 3 months, 6 months, and 12 months. Treatment was stopped after 9 months, and blood work was repeated at 12 months. Treatment was reinstituted at 1 year if requested by the parents. The enrollment goal was 30 patients; however, support from the pharmaceutical company was withdrawn when Rhone-Poulenc Rorer was taken over by Aventis. The investigational review boards of the participating centers approved the protocol and consent forms. Results: Seven patients received riluzole and 3 received placebo medication. All 3 patients in the placebo group died (mean age, 9 months). Three of 7 who received active drug are still living at ages 51/3 years, 4 years, and 30 months. None of the 10 subjects experienced adverse effects or changes in laboratory test results. None showed any change in motor abilities. Conclusions: Riluzole appears to be safe in young children. This was a limited study with insufficient power to show a difference between the 2 groups. Because there is a suggestion of possible benefit in treated subjects, we recommend further study of riluzole in pediatric patients with SMA.