An Antibody–Oligonucleotide Conjugate for Myotonic Dystrophy Type 1

BACKGROUND: mRNA. METHODS: In this phase 1-2, multicenter, double-blind, randomized, placebo-controlled trial, we assigned participants with myotonic dystrophy type 1 to receive del-desiran intravenously in a single dose (1 mg per kilogram of body weight) or three doses (2 mg or 4 mg per kilogram) or placebo. The primary end point was safety, and secondary end points were the pharmacokinetic and pharmacodynamic profiles of del-desiran and changes in downstream aberrant splicing patterns at 43 days in the 1-mg group and at 92 days (49 days after the second dose) in the 2-mg and 4-mg groups. RESULTS: mRNA levels in muscle-biopsy samples was -46% in the 1-mg group, -44% in the 2-mg group, -37% in the 4-mg group, and 0.9% in the placebo group. Maximum plasma concentrations of small interfering RNA (siRNA) and the area under the curve increased proportionally with dose escalation, and a minor fraction of siRNA was recovered in urine. Reductions in the mean composite missplicing score from baseline were 3%, 17%, 16%, and 7%, respectively, consistent with amelioration of missplicing in the 2-mg and 4-mg groups. CONCLUSIONS: Our results are consistent with delivery of del-desiran to muscle and amelioration of aberrant alternative splicing in some patients with myotonic dystrophy type 1; two serious adverse events occurred. These data support further clinical investigation. (Funded by Avidity Biosciences; ClinicalTrials.gov number, NCT05027269.).