What is X-Linked Retinitis Pigmentosa (XLRP)?
Retinitis pigmentosa (RP) describes a group of rare genetic eye diseases that damage light-sensitive cells in the retina, leading to loss of sight over time. In about 10% of RP cases, the non-working gene is passed down from the mother to her children resulting in a form of RP known as X-Linked RP (XLRP). For more information about how retinitis pigmentosa is inherited and the impact on the vision of male and female children, please go to https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/retinitis-pigmentosa.
XLRP causes gradual vision loss in boys and young men. The disease begins with night blindness and is followed by a slow narrowing of the peripheral field of vision. In general, the decline in vision (also referred to as “visual acuity”) results in a person becoming legally blind in their 40s.
How is XLRP diagnosed?
A clinical exam by a qualified healthcare professional, followed by genetic testing, can identify if a person has inherited RP, including XLRP. There are many reasons to get tested to identify the genetic cause of a person’s RP:
- Results from genetic testing can help patients understand the viability of currently available treatment approaches for RP and XLRP.
- Clinical trials to treat XLRP with gene therapy are being conducted to evaluate this investigational treatment approach, which may be a viable option for eligible patients.
- People with an accurate diagnosis can better understand how their vision may change in the future.
- With the help of a genetic counselor, they can understand the risk of passing a disorder onto their children.
Not all laboratories are able to detect the genetic mutations associated with XLRP. For more information about genetic testing and the process to obtain free testing, please go to https://www.fightingblindness.org/open-access-genetic-testing-program
What is gene therapy for XLRP?
Gene therapy is the process of injecting a person with a healthy gene to replace a damaged or mutated one. AGTC’s current clinical trial for XLRP involves an experimental procedure with an investigational (not yet FDA-approved) study drug designed to replace the mutated RPGR gene that causes XLRP. The purpose of the clinical trial, named SKYLINE, is to demonstrate whether the investigational study drug will help a person see better or maintain their current vision.
Phase 1/2 Clinical Trial
We completed enrollment of 28 patients in the Phase 1/2 clinical trial in which participants received a single dose of AGTC-501 in one eye to obtain initial data about safety and potential effectiveness of AGTC-501. The 6 and 12 month post treatment data results of the trial suggested potential benefit in improvement in several vision tests in some participants who received either a low or high dose of AGTC-501. Data from all 28 patients across six dose groups continue to demonstrate a favorable safety profile with no dose-limiting inflammatory responses observed. We are conducting two additional clinical trials, SKYLINE and VISTA, to further evaluate safety and efficacy in patients with XLRP.
The SKYLINE Trial
SKYLINE, now completed, was the Phase 2 follow-on study to assess to what extent each of the two doses, both of which suggested potential benefit in some participants enrolled in the original Phase 1/2 study, demonstrated improvement in a participants’ vision and other symptoms of XLRP. The study was performed by injecting one of the two doses of the study drug into one eye of the participant. Skyline enrolled 14 male participants where neither the participant nor the investigator knew which dose the participant will receive.
What is the VISTA Trial?
VISTA is a Phase 2/3 study to assess the effect of AGTC-501 on the symptoms of retinitis pigmentosa in additional patients with XLRP. If a patient meets the eligibility criteria, he will be randomly assigned to one of two “treatment” groups – either the lower-dose treatment group, the higher-dose treatment group, or a third group, called an “untreated control group”. Patients assigned to a treatment group will receive the study drug by injection into one eye. Patients assigned to the untreated control group will be observed for one year before they receive the treatment. As part of the study design, neither the participant nor the investigator will know which dose the participant will receive.
Key Eligibility Criteria for VISTA
An individual with XLRP may be able to participate in this trial if he meets the following requirements:
- Is a male with a diagnosis of X-Linked Retinitis Pigmentosa confirmed by a qualified healthcare professional
- Has a mutation in the RPGR gene confirmed by genetic testing
- Is between the age of 13 and 50 years old at the time of screening
- Has a best corrected visual acuity no better than 20/32 and no worse than 20/200 on an eye chart in one eye
How to Learn More About the VISTA Clinical Trial:
For HealthCare Providers:
If you are a HealthCare Provider who is interested in obtaining more information about the VISTA clinical trial, including how your patients might participate.
If you are an individual with XLRP or know someone with XLRP who may be interested in participating in the VISTA Trial
- Talk to your doctor about the potential risks and benefits of participating in an investigational gene therapy trial. Click here for questions and more information to help guide a conversation with your doctor.
- If you have not received genetic testing for your RP, please contact your doctor to discuss no-cost genetic testing.
- If you have already received genetic testing for your RP, contact your doctor to obtain a copy of your genetic test report, as well as a copy of your most recent medical and ophthalmic records. These records will be requested by the investigators to assess your initial eligibility for the trials.