Recently, exon skipping therapy has been attracting attention as a treatment for Duchenne muscular dystrophy (DMD) patients. This therapy uses a synthesized antisense oligonucleotide designed to skip the specific exon to change out-of-frame mutation to in-frame in the dystrophin mRNA, thereby inducing the expression of a shorter but functional dystrophin protein. NS-089/NCNP-02 is a novel phosphorodiamidate morpholino oligomer discovered by NCNP and Nippon Shinyaku Co., Ltd. NS-089/NCNP-02 targets exon 44 to serve as an effective treatment for DMD patients amenable to exon 44 skipping. The trial was designed in two parts. First-in-man part 1 is a stepwise dose-finding stage (4 weeks). Part 2 is a 24-week evaluation period based on the dosages determined during Part 1. In Part 1 of the study, Cohort 1 (three patients) will initially receive NS-089/NCNP-02 at dosing Level 1 (1.62 mg/kg QW) for two weeks and at dosing Level 3 thereafter (40 mg/kg QW) for two weeks. Cohort 2 (three patients) will initially receive NS-089/NCNP-02 at dosing Level 2 (10 mg/kg QW) for two weeks and at dosing Level 4 thereafter (80 mg/kg QW) for two weeks. In Part 2 of the study, two different doses of NS-089/NCNP-02 (determined from the results of Part 1) will be intravenously administered QW for 24 weeks. Patients who have completed Part 1 are allowed to participate in Part 2, and total 6 subjects were assigned to this study.　The primary endpoints are safety, and the secondary endpoints include expression of dystrophin protein, motor function assessments, exon 44 skipping efficiency, plasma and urinary NS-089/NCNP-02 concentrations, and changes in blood creatine kinase levels. In this conference, we report data on the safety, efficacy and pharmacokinetics of NS-089/NCNP-02 obtained by this study.