A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism

Purpose: To evaluate effectiveness of elamipretide in Barth syndrome (BTHS), a genetic condition of defects in TAZ, which causes abnormal cardiolipin on the inner mitochondrial membrane. Methods: We performed a randomized, double-blind, placebo-controlled crossover trial followed by an open-label extension in BTHS to test the effect of elamipretide, a mitochondrial tetrapeptide that interacts with cardiolipin. In part 1, 12 subjects were randomized to 40 mg per day of elamipretide or placebo for 12 weeks, followed by a 4-week washout and then 12 weeks on the opposite arm. Ten subjects continued on the open-label extension (part 2) of 40 mg per day of elamipretide, with eight subjects reaching 36 weeks. Primary endpoints were improvement on the 6-minute walk test (6MWT) and improvement on a BTHS Symptom Assessment (BTHS-SA) scale. Results: In part 1 neither primary endpoint was met. At 36 weeks in part 2, there were significant improvements in 6MWT (+95.9 m, p = 0.024) and BTHS-SA (-2.1 points, p = 0.031). There were also significant improvements in secondary endpoints including knee extensor strength, patient global impression of symptoms, and some cardiac parameters. Conclusion: In this interventional clinical trial in BTHS, daily administration of elamipretide led to improvement in BTHS symptoms.