Del-desiran is an experimental drug for myotonic dystrophy type 1 (DM1) that was tested in the MARINA clinical trial on 38 adult patients[1]. The drug effectively delivered siRNA to muscle and achieved an approximately 40% reduction in DMPK mRNA, leading to an improvement in gene mis-splicing[1]. The study showed improvements in several areas including myotonia (muscle stiffness), muscle strength and function, mobility and patient self-report[1]. The safety profile was acceptable, with most adverse events being mild or moderate in severity, with only two serious adverse events occurring in the higher dose groups[3]. Del-desiran has received Breakthrough Therapy, Orphan Drug, and Fast Track designations from the FDA, as well as Orphan designation from European and Japanese regulators[3]. The results of the study were published in The New England Journal of Medicine on February 19, 2026 and suggest that this drug could be the first globally approved drug for DM1[1].