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Exhibit 99.1 ProQR Announces Positive Results from Clinical Trial of QR - 421a in Usher Syndrome and Plans to Start Pivotal Trials QR - 421a demonstrated a concordant benefit in multiple measures of vision , including best corrected visual activity ( BCVA ) , static perimetry , and retinal imaging ( OCT ) QR - 421a observed to be well tolerated with no serious adverse events reported Two pivotal Phase 2/3 trials are expected to start by the end of 2021 Management to host a conference call today at 8:15 am EDT LEIDEN , Netherlands & CAMBRIDGE , Mass . , March 24 , 2021 -- ProQR Therapeutics N.V. ( Nasdaq : PRQR ) ( the “ Company ” ) , a company dedicated to changing lives through the creation of transformative RNA therapies for inherited retinal diseases ( IRDs ) , today announced results from a planned analysis of its Phase 1/2 Stellar trial of QR - 421a in adults with Usher syndrome and non - syndromic retinitis pigmentosa ( nsRP ) due to USH2A exon 13 mutations . In the trial , QR - 421a demonstrated benefit on multiple measures of vision that moved in concordance , including visual acuity , visual fields , and optical coherence tomography ( OCT ) retinal imaging , after a single dose . QR - 421a was observed to be well tolerated with no serious adverse events reported . Based on these findings , the Company plans to advance QR - 421a to two parallel pivotal Phase 2/3 trials by year end 2021 - one in early - moderate patients , one in advanced patients . " We're pleased to have met all the objectives we set for the Stellar trial , including determining suitable registration endpoints , the dose , dosing interval , and patient population for the Phase 2/3 pivotal trials , " said Aniz Girach , MD , Chief Medical Officer of ProQR , " With just a single dose , QR - 421a demonstrated clinical proof of concept with benefit observed in treated eyes compared to the untreated eyes in multiple concordant measures of vision . As expected , we saw benefits in both advanced and early - moderate patients in this slow progressing , debilitating eye disease , allowing us to advance this important investigational therapy for all patients with Usher syndrome and nsRP due to USH2A exon 13 mutations . Based on preliminary Regulatory guidance , we plan to submit protocols to advance QR - 421a to pivotal testing . This is our second program targeting a severe inherited retinal disease that is moving into pivotal trials , which we believe further validates our RNA therapy platform and our capabilities to design and efficiently take these programs through clinical development . " “ The safety profile and efficacy findings for QR - 421a are very encouraging , ” said 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 . " Usher syndrome and non - syndromic retinitis pigmentosa due to USH2A exon 13 mutations are devastating retinal diseases representing a high unmet medical need , as there are no approved therapies to treat the severe vision loss associated with these diseases . Patients ' biggest hope for a therapy is to stop disease progression and prevent vision loss , and these findings suggest that QR - 421a has the potential to stabilize vision . I look forward to this exciting program advancing into pivotal trial development . ”