Prosensa Reports Initial Findings From The Further Clinical Data Analyses Of Drisapersen For The Treatment Of Duchenne Muscular Dystrophy

Leiden, The Netherlands, Jan. 16, 2014 (GLOBE NEWSWIRE) -- Prosensa Holding N.V. (NASDAQ: RNA), the Dutch biopharmaceuticalcompany focusing on RNA-modulating therapeutics for rare diseaseswith high unmet medical need, today announced initial findings fromfurther analyses from the aggregate data from the clinicaldevelopment program of drisapersen for the treatment of DuchenneMuscular Dystrophy (DMD).

"We are encouraged by these results that suggestthat treating earlier in the disease and treating longer shows adelay in the progression of the disease," said Hans Schikan,Prosensa's Chief Executive Officer. "These data encourage us toengage patient groups, clinical experts and regulators to explore apath forward for drisapersen, which includes the possibility ofre-dosing."

Schikan will be presenting details of thefurther data analyses at the 32 nd Annual J.P. MorganHealthcare Conference in San Francisco on Thursday, January 16,2014 at 10:00 AM Pacific Time. A live webcast of the presentationcan be accessed through the Investors & Media section of theProsensa corporate website at http://ir.prosensa.eu/events.cfm and will be archived for 90 days.

With data from more than 300 patients Prosensahas the largest clinical data set in DMD. In order to advance thegeneral understanding of DMD, Prosensa has also announced that itwill make certain data from the drisapersen clinical programavailable to the scientific community. In addition it has initiateda study to better understand the natural history of DMD and is alsoexploring potential biomarkers that could be of use as indicatorsof efficacy in DMD clinical trials.

The subset analyses focus on outcomes in DMDboys seven years or younger and those over seven years old asmeasured by the six-minute walk test (6MWT). In all studies, atreatment difference was seen in the younger patientpopulation.

Notably, the preliminary analysis of the 96 weekextension data from those participating in the phase III DMD114044(DEMAND III) study shows a 49 meter difference between those oncontinual treatment (n=52) and those who had been on placebo for 48weeks followed by active drug (n=31).  Those previouslyparticipating in the DMD114117 study (DEMAND II) showed a 52 meterdifference at 96 weeks (n=13, n=17, respectively).

Key safety findings are consistent with previousobservations, including injection site reactions, proteinuria andmild to severe thrombocytopenia.

Schikan concludes, "We will continue to work closely withpatient groups, clinical experts and regulators to ensure that weleave no stone unturned to bring treatments to boys affected byDMD."

About drisapersen and the clinicaldevelopment program

Drisapersen, (previously GSK2402968/PRO051), anantisense oligonucleotide which induces exon skipping of exon 51,is currently in-late stage development for DMD. Drisapersen hasorphan drug status in the EU, US, Australia and Japan. In June2013, drisapersen was granted Breakthrough Therapy designation bythe US Food and Drug Administration.

The overall drisapersen clinical programcomprises three double-blind, placebo-controlled studies(DMD114117, DMD114876 and DMD114044) and two long term open-labelextension studies (DMD114673 and DMD114349).

For more information regarding the ongoingclinical studies involving drisapersen visit www.clinicaltrials.gov.

About DMD

Duchenne Muscular Dystrophy (DMD) is a severelydebilitating childhood neuromuscular disease that affects up to 1in 3,500 live male births. This rare disease is caused by mutationsin the dystrophin gene, resulting in the absence or defect of thedystrophin protein. Patients suffer from progressive loss of musclefunction, often making them wheelchair bound before the age of 12.Respiratory and cardiac muscle can also be affected by the disease.Few patients survive the age of 30.

About exon skipping

The dystrophin gene is the largest gene in thebody, consisting of 79 exons. Exons are small sequences of geneticcode which lead to the manufacture of sections of protein. In DMD,when certain exons are mutated/deleted, the RNA cannot read thegenetic code past the fault. This prevents the rest of the exonsbeing read, resulting in a non-functional dystrophin protein andthe severe symptoms of DMD.

RNA-based therapeutics, specifically antisenseoligonucleotides inducing exon skipping, are currently indevelopment for DMD. This technology uses synthetic antisenseoligonucleotides to skip an exon next to a deletion and therebycorrect the reading frame, enabling the production of a noveldystrophin protein. Up to 13% of boys with DMD have dystrophin genemutation/deletions amenable to an exon 51 skip.

About Prosensa Holding N.V.

Prosensa (NASDAQ: RNA) is a Dutch biotechnology company engagedin the discovery and development of RNA-modulating therapeutics forthe treatment of genetic disorders. Its primary focus is on rareneuromuscular and neurodegenerative disorders with a large unmetmedical need, including Duchenne muscular dystrophy, myotonicdystrophy and Huntington's disease.

www.prosensa.com

Forward Looking Statements

This press release contains certainforward-looking statements.  All statements, other thanstatements of historical facts, contained in this press release,including statements regarding our strategy, future operations,future financial position, future revenues, projected costs,prospects, plans and objectives of management, are forward-lookingstatements. The words "anticipate," "believe," "estimate,""expect," "intend," "may," "plan," "predict," "project," "target,""potential," "will," "would," "could," "should," "continue," andsimilar expressions are intended to identify forward-lookingstatements, although not all forward-looking statements containthese identifying words. Forward-looking statements in this pressrelease include statements around our exon -skipping drugcandidates. Actual results may differ materially from thoseprojected or implied in such forward-looking statements. Suchforward-looking information involves risks and uncertainties thatcould significantly affect expected results.  These risks anduncertainties are discussed in the Company's SEC filings,including, but not limited to, the Company's Form 6-K containingthis press release and certain sections of the Company'sRegistration Statement on Form F-1. In addition, anyforward-looking statements represent our views only as of today andshould not be relied upon as representing our views as of anysubsequent date. While we may elect to update these forward-lookingstatements at some point in the future, we specifically disclaimany obligation to do so, even if our views change.
CONTACT: Prosensa Holding N.V.         Celia Economides, Senior Director IR & Corporate Communications         Phone: +1 917 941 9059         Email: c.economides@prosensa.nl

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