Epicrispr Biotechnologies has reported interim results from an ongoing Phase 1/2 clinical trial showing increased muscle volume in patients with facioscapulohumeral muscular dystrophy (FSHD) treated with its investigational therapy EPI-321. The company said the findings represent the first reported clinical evidence of a therapy increasing muscle volume in patients with the disease, which currently has no approved treatments.
The open-label first-in-human study is evaluating EPI-321, an epigenetic therapy designed to silence DUX4, the genetic driver of FSHD. As of the May 12, 2026 data cutoff, nine patients had received treatment across two dose groups. Six patients were treated with a single intravenous infusion at a dose of 2×10¹³ vg/kg, while three patients received a higher dose of 4×10¹³ vg/kg.
Among the first three evaluable patients in the lower-dose group, all showed increases in lean muscle volume six months after treatment compared with baseline measurements. According to the company, the patients experienced an average gain of approximately 370 mL of lean muscle volume, equivalent to about 0.8 pounds of muscle mass. Individual increases ranged from roughly 0.5 pounds to 1.3 pounds, with some muscles showing gains of up to 15% in lean muscle volume.
The therapy demonstrated a favorable safety profile in the study, with no serious adverse events reported to date. Epicrispr also noted that the MRI findings were accompanied by reductions in a circulating cell-free DNA biomarker associated with DUX4 pathway activity. The company said these biomarker changes were directionally consistent with the increases observed in muscle volume, as well as favorable trends in strength and functional measures previously reported at the three-month assessment.
FSHD is a progressive neuromuscular disorder characterized by muscle weakness and degeneration. According to Epicrispr, the condition affects approximately 870,000 people worldwide and commonly impacts muscles of the face and upper body, although other muscle groups can also be affected. The company said patients in previous FSHD clinical studies have generally experienced ongoing muscle loss over time, in contrast to the increases in muscle volume observed across evaluable patients treated with EPI-321 at six months.
EPI-321 uses Epicrispr’s Gene Expression Modulation System platform and is intended to provide long-lasting suppression of DUX4 activity without changing the underlying DNA sequence. The therapy employs a viral vector to deliver an enzyme that adds methyl groups to the DUX4 gene, a process intended to silence its expression. Epicrispr has said the therapy is intended to provide durable protection against DUX4-driven muscle damage.
“These results represent a major scientific breakthrough for both the FSHD community and the field of epigenetic medicine,” said Amber Salzman, Ph.D., chief executive officer of Epicrispr Biotechnologies.
Russell Butterfield, M.D., principal study investigator and associate professor in pediatrics and neurology at the University of Utah, said patients with FSHD experience progressive muscle loss that affects many aspects of daily life. He added that while the results remain early and require further follow-up, the observed increases in lean muscle volume suggest EPI-321 may be addressing underlying disease mechanisms.
MRI analyses for the study were conducted in collaboration with Springbok Analytics. Silvia Blemker, Ph.D., the company’s chief scientific officer, said the MRI findings were consistent across all evaluable patients and enabled objective measurement of muscle-volume changes across as many as 140 muscles throughout the body.
The ongoing trial, identified as NCT06907875, is assessing the safety, tolerability, biological activity, and preliminary efficacy of EPI-321 in adults with FSHD. Epicrispr expects to present additional data at the World Muscle Society Annual Congress in September 2026 and complete the primary portion of the study in mid-2027.
Several companies are pursuing potential FSHD therapies. Sanofi’s licensed candidate losmapimod failed in a Phase 3 trial in 2024, while Genentech discontinued a Phase 2 study of emugrobart after the treatment did not consistently produce the expected improvements in muscle growth and function. Other companies developing potential FSHD therapies include Sarepta Therapeutics, with an siRNA candidate licensed from Arrowhead Pharmaceuticals, and Novartis, which acquired an RNA-based program through its acquisition of Avidity Biosciences.
Epicrispr has announced promising early-stage clinical data demonstrating increased muscle volume in patients receiving EPI-321 for the treatment of facioscapulohumeral muscular dystrophy (FSHD). The preliminary findings mark an important milestone for Epicrispr as the company advances its innovative CRISPR-based gene regulation platform aimed at treating rare genetic diseases.
The results suggest that EPI-321 has the potential to address the underlying cause of FSHD while supporting improvements in muscle health and function.
Epicrispr Announces Positive Early Clinical Results
The latest findings from Epicrispr indicate that patients treated with EPI-321 experienced measurable increases in muscle volume during the early stages of the clinical trial. Researchers are evaluating both safety and biological activity to determine whether these changes translate into meaningful functional improvements over time.
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