A Study of ATSN-201 Gene Therapy for Patients with X-linked Retinoschisis (RS1-associated) to Assess Safety and Visual Function

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What is this study about?

The study focuses on a rare inherited eye condition called RS1-associated X-linked Retinoschisis, which is caused by a problem with the RS1 gene and leads to progressive loss of vision. The investigational therapy is a gene‑delivery product named ATSN-201, which contains an adeno-associated viral vector serotype 44.9 containing the human HRS1 gene and is given as a single injection under the retina. The purpose of the study is to determine the effect of ATSN-201 on visual function.

Participants will receive the injection in one eye and will be followed for several months to assess changes in vision. Simple eye tests will be used, such as a test that measures light sensitivity across the retina (microperimetry), a scan that provides detailed pictures of retinal layers (spectral domain optical coherence tomography), and standard reading charts that evaluate sharpness of vision (best-corrected visual acuity and low luminance visual acuity measured with ETDRS charts). Additional questionnaires will ask about daily visual abilities and overall impression of change. Safety will be monitored by recording any unwanted effects.

1 enrollment and study identification

after signing the consent form, you receive a study identification number and a schedule for the first set of examinations.

2 baseline eye examinations

you undergo a series of tests to record the condition of the study eye before any treatment.

tests include microperimetry (measures light sensitivity at specific spots), spectral domain optical coherence tomography (sd‑oct) imaging, best‑corrected visual acuity (bcva) and low‑luminance visual acuity (llva) using the etdrs chart, reading speed measurement with mnread, and questionnaires such as the michigan retinal degeneration questionnaire and the cardiff visual ability questionnaire for children.

3 randomization and preparation for injection

if the study design requires random assignment, you are placed into the appropriate group.

the study team prepares the atsn-201 gene‑therapy product for delivery.

4 subretinal injection of atsn-201

a single dose of atsn-201 is injected into the space beneath the retina of the study eye.

the dose is 11000000000 vector genomes per milliliter, delivered as a concentrated solution for injection.

the procedure is performed by a retinal surgeon using a subretinal route.

5 immediate post‑procedure monitoring

after the injection you are observed for several hours to ensure there are no immediate safety concerns.

vital signs and the injected eye are checked regularly during this period.

6 follow‑up visits for safety and efficacy assessments

you return for scheduled visits after the injection. at each visit the same tests performed at baseline are repeated to monitor changes.

these visits include microperimetry, sd‑oct imaging, visual acuity measurements, reading speed testing, and the relevant questionnaires.

the schedule follows the study protocol, typically at weeks and months after treatment and continues for the duration of the trial.

7 long‑term monitoring

the study continues with periodic assessments for several years to evaluate the lasting effect of the gene therapy and to record any delayed adverse events.

Who Can Join the Study?

You must be at least 6 years old.
You must be a genetically male patient who has been given a clinical diagnosis of X‑linked retinoschisis (XLRS) caused by a disease‑causing change (called a pathogenic or likely pathogenic mutation) in the RS1 gene, or you must be a genetically female patient with the same diagnosis caused by two disease‑causing changes (one on each copy of the RS1 gene, known as biallelic mutations).
Your best corrected visual acuity (BCVA) must be between 34 and 73 letters on the ETDRS chart, which is similar to a Snellen acuity of about 20/200 to 20/40 (a measure of how clearly you can see at a distance).
Eye imaging with spectral‑domain optical coherence tomography (SD‑OCT) must show a split in the central retina called foveal schisis.

Who Cannot Join the Study?

You must not have taken any carbonic anhydrase inhibitor medicine (a drug that lowers eye pressure) by mouth or as eye drops within one month before the screening visit.
You must not have participated in a previous eye gene or cell therapy study.
You must have a presence of macular schisis (a splitting of the central part of the retina); if this is absent, you cannot join.
Your best corrected visual acuity (BCVA) cannot be better than 75 ETDRS letters (which is roughly the same as a Snellen acuity of 20/32, meaning you see slightly worse than normal vision).
You cannot have existing eye problems that greatly raise the risk of vision loss from the study’s subretinal injection, such as advanced glaucoma (severe pressure damage to the optic nerve), optic neuropathy (damage to the nerve that carries visual signals), uveitis (inflammation inside the eye), or a history of corneal transplant surgery (replacement of the clear front part of the eye).
You must not have had any intraocular surgery (eye surgery inside the eye), including laser treatment, within six months before screening, and you cannot plan to have any such surgery during the first 12 months of the study.

Where you can join this trial?

Verified and Recommended Sites

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Verified Sites

Site Name	City	Country
Azienda Sociosanitaria Territoriale Santi Paolo E Carlo	Milan	Italy
Azienda Ospedaliera Universitaria Universita’ Degli Studi Della Campania Luigi Vanvitelli	Naples	Italy
Hospital Universitario Fundacion Jimenez Diaz	Madrid	Spain
Hospital Sant Joan De Deu Barcelona	Esplugues De Llobregat	Spain

Other Sites

No sites found in this category

Trial status

Country	Status	Recruitment Start
Belgium	Not yet recruiting	19.10.2026
Italy	Not yet recruiting	19.10.2026
Spain	Not yet recruiting	19.10.2026

Trial locations

ATSN-201 is a gene‑therapy medicine that is given as a tiny injection under the retina (the back part of the eye). It uses a harmless virus to carry a normal copy of the HRS1 gene into the eye’s cells. The goal is to replace the faulty gene that causes X‑linked retinoschisis, a condition where the retina splits and vision gets worse. By delivering the correct gene, the treatment hopes to improve the structure of the retina and help patients see better. This therapy is being studied in a clinical trial to see if it is safe and works well for people with this rare eye disease.

X-linked retinoschisis – This is an inherited eye disorder caused by mutations in the RS1 gene. It usually appears in early childhood and leads to a splitting of the retinal layers, especially in the central retina. The separation disrupts normal retinal function, resulting in reduced visual acuity and difficulty seeing fine detail. Over time, the condition can cause additional changes such as peripheral retinal holes or reduced peripheral vision. The disease often progresses slowly, with gradual worsening of visual performance.

Trial ID:

2026-525886-38-00

Protocol code:

ATSN-201-1

NCT ID:

NCT05878860

Trial Phase:

Therapeutic confirmatory (Phase III)

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A Study of ATSN-201 Gene Therapy for Patients with X-linked Retinoschisis (RS1-associated) to Assess Safety and Visual Function

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?