Biotechnology company Stealth BioTherapeutics (NASDAQ: MITO) said on Tuesday that it has received encouraging results from the open-label extension of the Phase 2/3 TAZPOWER study of elamipretide, an investigational drug, in patients with genetically confirmed Barth syndrome.

Barth syndrome is an ultra-rare mitochondrial disease in which reduced levels of the mitochondrial phospholipid cardiolipin are associated with skeletal muscle weakness, debilitating fatigue, cardiac abnormalities, recurrent infections, delayed growth as well as reduced life expectancy.

The company stated that the TAZPOWER open-label results was presented at the 2019 MDA Clinical & Scientific Conference.

TAZPOWER was a Phase 2/3 crossover study of elamipretide in 12 patients with Barth syndrome followed by an open-label extension in which 10 of the 12 patients participated. The study demonstrated improvements in various endpoints and suggests that a longer duration of elamipretide therapy is important for patients with lower baseline levels of normal cardiolipin. Almost 40% decrease in the average ratio of abnormal to normal cardiolipin was observed from the start of the study to week 12.

Although statistical significance was not achieved in the intent-to-treat population during the blinded, placebo-controlled portion of the study, a pre-specified analysis of subjects with relatively higher levels of normal cardiolipin showed improvement on several endpoints, revealed the company.

According to the company,the primary endpoints included change in distance walked during the 6MWT and change in the BTHS-SA Total Fatigue score.