Novartis announced that delpacibart braxlosiran met primary and key secondary biomarker endpoints in the Phase 1/2 FORTITUDE study for facioscapulohumeral muscular dystrophy. The investigational antibody oligonucleotide conjugate is being evaluated as a potential disease-modifying therapy for a condition that currently has no approved treatments.
Novartis reported positive results from the biomarker cohort of its Phase 1/2 FORTITUDE study evaluating delpacibart braxlosiran (del-brax) in patients with facioscapulohumeral muscular dystrophy (FSHD), a rare neuromuscular disease characterized by progressive muscle weakness and disability. The company announced that the study met both its primary and key secondary endpoints, providing additional evidence supporting the investigational therapy's disease-modifying potential.¹
“These results validate the dosing regimen implemented in our Phase III trial and lend further evidence of the potential for del-brax to have a significant impact for people with FSHD.”
— Nazem Atassi, Global Head, Neuroscience and Gene Therapy Development, Novartis
The FORTITUDE biomarker cohort demonstrated reductions in plasma KHDC1L, a DUX4-regulated circulating biomarker, as well as reductions in creatine kinase levels, a marker of muscle damage. According to Novartis, these findings indicate strong target engagement and suggest a reduction in ongoing muscle injury.¹
“The FORTITUDE biomarker cohort data importantly replicate the target engagement and downstream muscle protection seen with del-brax in earlier dose-escalation cohorts,” said Nazem Atassi, Global Head of Neuroscience and Gene Therapy Development at Novartis.¹
FSHD is among the most common forms of muscular dystrophy and is caused by abnormal expression of the DUX4 gene. The condition affects an estimated 45,000 to 87,000 people across the United States and Europe and currently has no approved therapies. Patients typically develop symptoms during adolescence or early adulthood, experiencing progressive muscle weakness, pain, fatigue, and loss of mobility. Approximately one in five patients ultimately becomes wheelchair dependent.²
Del-brax is designed to address the underlying cause of FSHD by suppressing DUX4 expression. The therapy utilizes an antibody oligonucleotide conjugate (AOC) platform, which combines monoclonal antibody targeting with small interfering RNA (siRNA) technology to deliver gene-silencing therapy directly to muscle cells. This targeted approach aims to reach tissues that have historically been difficult to access with RNA therapeutics.¹
The biomarker findings also helped validate the dosing regimen selected for the ongoing Phase 3 FORTITUDE-3 trial. Based on results from earlier dose-escalation cohorts, investigators selected a 2 mg/kg dose administered every six weeks for both Cohort C and the pivotal study.¹
FORTITUDE-3 is currently enrolling approximately 200 patients between the ages of 16 and 70 years. The randomized, double-blind, placebo-controlled trial will evaluate both functional and patient-reported outcomes, including quantitative muscle testing and mobility assessments.¹
The positive update represents another milestone in Novartis' expanding neuromuscular pipeline, which was strengthened following its acquisition of Avidity Biosciences in February 2026. The acquisition added three late-stage antibody oligonucleotide conjugate programs targeting rare neuromuscular disorders, including FSHD, myotonic dystrophy type 1, and Duchenne muscular dystrophy.¹
Novartis stated that it plans to engage with global regulatory authorities regarding the Phase I/II findings while continuing enrollment in the Phase III study.¹
