Dear Duchenne Community,

We want to provide you with an update on the progress of SolidBiosciences IGNITE DMD Phase I/II clinical trial for our investigational microdystrophin gene transfer, SGT-001. Since we communicated preliminary clinical data in February, we advanced the study to evaluate SGT-001 at a higher dose in the second cohort of patients. As a reminder, IGNITE DMD is a single ascending dose clinical trial, meaning that it is designed to evaluate progressively higher doses of SGT-001. Based on our preclinical data, we believe that higher doses of SGT-001 will express more microdystrophin. This new dose, 2E14 vg/kg, is four times higher than our starting dose of 5E13 vg/kg.

Recently, the first two patients in this higher dose cohort were enrolled, one randomized to the treatment group and one randomized to the delayed-treatment control group. Similar to others who have received SGT-001, the patient in the treatment arm experienced a transient decline in platelet count shortly after dosing, which fully resolved. He was also diagnosed with a non-SGT-001-related gastrointestinal infection, which responded to treatment. We observed transient abnormalities on laboratory tests that measure liver function that quickly responded to an increased dose of oral steroids. We notified the FDA and can share with you that the patient is doing well and has resumed his normal activities.

IGNITE DMD is ongoing and continues to be open for enrollment at the University of Florida. We are pleased to share new U.S. clinical sites will be coming on board, including the University of Massachusetts Memorial Medical Center, led by Dr. Brenda Wong. Activities are underway to begin enrollment. For information on inclusion and exclusion criteria for IGNITE DMD and additional details on screening, we encourage you to visit clinicaltrials.gov.

We believe that SGT-001 has the potential to be an important therapy for patients with Duchenne, and we are working hard to progress SGT-001 through clinical development quickly and responsibly. We look forward to continuing to keep you updated as the study advances.