Clinical Trial News: Positive results in Usher syndrome and RP clinical study

ProQR news – Positive results achieved in our ongoing Usher syndrome and retinitis pigmentosa research.
March 24, 2021

Stellar study, Phase 1/2 clinical trial showed investigational RNA therapy QR-421a is effective and safe. ProQR plans to start final phase trials for people with USH2A mediated retinitis pigmentosa.

We are pleased to announce the positive results of our Usher syndrome and retinitis pigmentosa clinical study Stellar, which has met all its stated objectives. This marks a crucial milestone in our ongoing inherited retinal disease research.

The news published today is a substantial achievement in the clinical development focusing on Usher syndrome and RP. (Full press release can be found here:

Usher syndrome is a genetic condition characterized by both hearing loss up to deafness and the progressive loss of vision up to blindness. The loss of vision is an eye disease called retinitis pigmentosa (RP), which affects the light sensitive area of tissue on the back of the eye (the retina). There are three main types of Usher syndrome - type 1, type 2 and type 3. Each of these types has several different genes responsible for causing the syndrome.

There are currently no available treatments for the more than 16,000 patients with vision loss due to Usher syndrome 2A and RP due to USH2A exon 13 mutations.

QR-421a and the Stellar study

Our investigational RNA therapy, QR-421a, aims to stop vision loss or restore vision in people with a mutation in a specific part of the USH2A gene, called exon 13. QR-421a works by binding to the mutated USH2A RNA and exclude exon 13 from the RNA. This approach is known as exon skipping. The cells in the retina can then produce a slightly shorter but functional USH2A protein.

The Stellar study, is a Phase 1/2 clinical trial of QR-421a to test whether it is safe and leads to better vision.

The interim findings from the trial were encouraging, announced in March 2020. Today the positive results of the trial have been announced. With only one injection of QR-421a, the Stellar study showed benefit in the treated eye in comparison to the untreated eye across multiple eye tests. We have seen this benefit across all participants in the Stellar study, which included clinical trial participants with both advanced vision loss as well as early to moderate vision loss.

For more information on the safety & efficacy of the trial, please read our Community Statement QR421a program results Mar2021.

ProQR has agreed with medical regulators to advance QR-421a into final stage clinical testing. This will be our second clinical program to move into the final stage, following our final stage clinical testing in Leber Congenital Amaurosis type 10 (LCA10). The news today further validates our RNA therapy platform and our capabilities to design and efficiently take these programs through clinical development.

A word from our patient partners

“We are pleased to see QR-421a advancing to pivotal testing and proud to support the work of ProQR.”

Benjamin R. Yerxa, PhD, Chief Executive Officer at the Foundation Fighting Blindness.

At ProQR we partner with over 20+ retinal patient organizations around the world. For more information on our partnerships and work we do with the patient community please email

A word from a physician

Robert Koenekoop, MD, MSc, PhD, FRCS(C), FARVO, a clinical scientist from the Montreal Children’s Hospital and Professor of the McGill University Faculty of Medicine and Department of Pediatric Surgery, outlined:

“The safety profile and efficacy findings for QR-421a are very encouraging.”

What does this mean?

Today is a robust validation of our RNA therapies to treat the high unmet need in the inherited retinal disease community. It now means we have seen that our RNA therapies work in providing visual benefit to clinical trial participants with both LCA10 and now Usher syndrome and RP.

What next?

Based on the news today, ProQR plans to conduct two final stage clinical trials or Phase 2/3 trials. We will work with regulators to submit clinical trial protocols for two final stage registration trials called Sirius and Celeste. 

If you have any questions, please consult your treating physician or you can contact ProQR at