Early clinical trial results show vision gains in patients with BEST1-related disease

Opus Genetics has shared encouraging early results from its ongoing Phase 1/2 clinical trial for OPGx-BEST1, a potential one-time gene therapy for people with BEST1-related retinal disease. All five patients enrolled in the clinical trial had clinically meaningful improvement in visual function, according to Opus Genetics. The greatest functional improvements were observed in participants with less advanced disease.

BEST1-related retinal diseases are rare inherited conditions caused by mutations in the BEST1 gene. Best vitelliform macular dystrophy (BVMD) and autosomal recessive bestrophinopathy (ARB) are two types of BEST1-related diseases. Over time, damage to cells in the retina leads to progressive vision loss. To date, neither condition has an approved treatment.

Early clinical trial results find improvements in vision

In the BIRD-1 clinical trial, five adult patients with BEST1-related disease were treated with a low dose of OPGx-BEST1, delivered through a sub-retinal injection in one eye. Three patients had BVMD and were evaluated three months after treatment. Two additional patients with ARB were evaluated six months after treatment. All patients in the clinical trial improved in at least one area of visual function, including best corrected visual acuity (3 of 5 patients), visual acuity in low light (2/5), contrast sensitivity (2/5), or how well the central retina detects light as measured through microperimetry (3/4). Four of five patients also showed improvements in the structure of the retina itself. No serious safety concerns emerged in this group and treatment-related adverse events were mild or moderate, according to Opus. 

Participants whose disease was less advanced when they entered the trial experienced the biggest gains, suggesting that treating BEST1-related disease earlier, before more retinal tissue is lost, could lead to better outcomes down the line.

How the gene therapy works

OPGx-BEST1 is a gene therapy designed to address the genetic cause of BEST1-related retinal disease. The treatment uses a modified virus called an AAV to deliver a healthy copy of the BEST1 gene to retinal pigment epithelial cells – the cells that support and nourish the retina’s light-sensing cells.

Next steps in bringing treatment to patients

Opus met with the U.S. Food and Drug Association in August 2026 to discuss plans for the final Phase 3 clinical trial. Opus and the FDA agreed on retinal sensitivity, measured by microperimetry, as part of the potential plan to measure if the treatment worked. This measure, together with a patient-reported outcome measure, will comprise what’s called the clinical trial’s endpoint. Opus expects to finalize its Phase 3 plans in early 2027 and to begin treating patients as part of the trial later that year. Opus has also already enrolled a second Phase 1/2 cohort of eight participants to receive a higher dose of OPGx-BEST1. Those results are expected in the second quarter of 2027.

Opus Genetics is a company founded by the Foundation Fighting Blindness and is a part of the Gund Vision Fund (formerly the Retinal Degeneration Fund) portfolio.