QR-421a and the clinical trials on Usher Syndrome Type 2A


ProQR is developing a novel investigational drug called QR-421a to treat RP in patients that have USH2 due to a mutation in a specific part of the USH2A gene, called exon 13. In the Western world there are approximately 16,000 patients that experience vision loss due to a mutation in exon 13 of the USH2A gene. QR-421a is designed to exclude exon 13 from the USH2A mRNA, thereby removing the mutation in exon 13. This approach is also known as exon skipping.

RNA is the “blueprint” for protein synthesis. Skipping of exon 13 in the “blueprint” is expected to lead to a shortened but functional usherin protein. By restoring functional usherin protein expression, QR-421a aims to treat the underlying cause of RP associated with USH2. QR-421a is intended to be administered via intravitreal (into the eye) injections.

Beyond QR-421a, we are developing QR-411, targeting the approximately 1,000 patients that have Usher syndrome due to the PE40 mutation (also known as c.7595-2144A>G) in USH2A.

Clinical trials

A first-in-human clinical trial of QR-421a is ongoing. The Phase 1/2 study, named STELLAR, will include approximately 18 patients that experience vision loss due to mutation(s) in exon 13 of the USH2A gene. The STELLAR study is planned to be conducted at expert centers in North America and select European countries. We expect the first interim results from this study to be available in the first quarter of 2020.

This phase 1/2 clinical trial is designed to evaluate the safety and tolerability of QR-421a. Patient benefit will be assessed as well.

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