Atsena Therapeutics has dosed the first patient in the Phase 3 pivotal cohort of its gene therapy ATSN-201 for X-linked retinoschisis, marking a key step forward in a rare inherited retinal disease with no approved treatments.

Atsena Therapeutics has begun Phase 3 pivotal dosing in its LIGHTHOUSE trial evaluating ATSN-201, a gene therapy for X-linked retinoschisis (XLRS), a rare inherited retinal disorder that causes progressive vision loss in childhood.

The company confirmed that the first patient has now been treated in the Phase 3 cohort, with rapid early recruitment already underway across North America and Europe.

Since opening enrolment in May, Atsena reports that around 10% of the planned 76-patient cohort has already been enrolled, with completion expected in the first quarter of 2027. Topline results are anticipated in the first half of 2028, with a Biologics License Application submission targeted for the second half of 2028.

The Phase 3 cohort follows earlier Phase 1/2 data from the LIGHTHOUSE study, which showed evidence of both structural and functional improvement in treated patients, including closure of retinal schisis cavities and improvements in measures of visual function that were sustained for at least one year.

The trial is evaluating ATSN-201 in both adult and paediatric patients, including children as young as six years old, and is designed as a randomised controlled study comparing treatment with observation over a 12-month period.

The primary endpoint is change in microperimetry at 52 weeks, supported by secondary endpoints including visual acuity and optical coherence tomography-based measures of retinal structure.

X-linked retinoschisis is caused by mutations in the RS1 gene and leads to splitting of retinal layers, resulting in reduced visual acuity that cannot be corrected with glasses and typically progresses towards blindness in affected males.

Approximately 30,000 individuals in the US and Europe are estimated to be affected, with no currently approved therapies available.

ATSN-201 uses AAV.SPR, a gene therapy vector designed to spread laterally across retinal tissue to improve delivery to photoreceptors in the central retina without requiring foveal detachment.

The company has described the programme as its lead gene therapy candidate and is also developing additional programmes in inherited retinal diseases, including Usher syndrome type 1B and Stargardt disease.

Atsena said the rapid enrolment reflects strong clinical interest in the programme and the urgent unmet need in XLRS, where patients currently have no disease-modifying treatment options.

The company plans to continue scaling recruitment across additional sites in North America and Europe as the trial progresses.