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Prosensa extends the re-dosing of drisapersen in Europe in patients with Duchenne muscular dystrophy

Prosensa extends the re-dosing of drisapersen in Europe in patients with Duchenne muscular dystrophy

Leiden, The Netherlands – 26 September, 2014 – Prosensa Holding N.V. (NASDAQ: RNA), the biopharmaceutical company focusing on RNA-modulating therapeutics for rare diseases with high unmet need, today announced that it has extended its comprehensive program of re-dosing of drisapersen in patients with Duchenne muscular dystrophy (DMD) into Europe, with the PRO051-02/DMD114673 sites re-opening, beginning with Belgium. This follows quickly on the re-dosing program that began in the United States (US) last week.

The two sites in the PRO051-02/DMD114673 extension study, the longest running study with a disease modifying therapy in DMD, had been treating boys with drisapersen for almost 4 years prior to dosing being suspended in September 2013. Efficacy data from 10 boys analyzed in this study at 177 weeks showed a mean change from their baseline six-minute walk test (6MWT) of only -25 meters, including two boys with more severe disease who lost ambulation early on in the study.

The re-dosing program in Belgium is being led by Dr. Nathalie Goemans, Head of the Neuromuscular Reference Center for Children at the University Hospitals Leuven (UHL) and in Sweden is led by Dr. Mar Tulinius, Professor and Chief Physician at the University of Gothenburg, both key investigators in various drisapersen studies.

Dr. Goemans welcomed the recommencement of dosing, commenting, “When natural history of the disease suggests that DMD boys lose between 40-60 meters in their 6MWT per year, the results from this long-running study are very encouraging in terms of walking ability and other measures of muscle function. Boys treated in our clinic are eager to get back onto drisapersen treatment since dosing was stopped last year.”

Prosensa is urgently progressing preparations to roll out similar programs of re-dosing in other European countries and globally for all previously treated drisapersen patients, via expanded access, compassionate use or named patient programs, where feasible.

Dr. Giles Campion, Prosensa's Chief Medical Officer said "Today’s news that Dr. Goemans has been able to resume dosing of boys with DMD is another step forward towards our goal of making drisapersen available to as many boys as possible in a timely manner. We are pleased that we have been able to accomplish this soon after re-dosing began in the US, and we anticipate Dr. Tulinius’ site to resume dosing imminently.”

In June, Prosensa announced that the US Food and Drug Administration (FDA) outlined a regulatory path forward for drisapersen, under an accelerated approval pathway, based upon existing data. “Prosensa remains on track to pursuing regulatory filings for drisapersen, initially in the US and Europe, with an FDA submission planned before the end of the year and an EMA submission shortly thereafter” re-confirmed Hans Schikan, Prosensa’s CEO.

Notes To Editors

About Prosensa Holding N.V.
Prosensa (NASDAQ: RNA) is a biotechnology company engaged in the discovery and development of RNA-modulating therapeutics for the treatment of genetic disorders. Its primary focus is on rare neuromuscular and neurodegenerative disorders with a large unmet medical need, including Duchenne muscular dystrophy (DMD), Myotonic dystrophy and Huntington's disease.

Prosensa's current portfolio includes six compounds for the treatment of DMD, all of which have received orphan drug status in the United States and the European Union. The compounds use an innovative technique called exon-skipping to provide a personalized medicine approach to treat different populations of DMD patients.

About DMD
Duchenne muscular dystrophy (DMD) is a severely debilitating childhood neuromuscular disease that affects up to 1 in 3,500 live male births. This rare disease is caused by mutations in the dystrophin gene, resulting in the absence or defect of the dystrophin protein. As a result, patients suffer from progressive loss of muscle strength, often rendering them wheelchair-bound before the age of 12. Respiratory and cardiac muscle can also be affected by the disease and most patients die in early adulthood due to respiratory and cardiac failure.

About the drisapersen clinical program
Drisapersen induces exon 51 skipping in the dystrophin gene and is intended for up to approximately 13% of all DMD patients. Drisapersen has been granted orphan designation in the European Union, the United States and Japan, and Breakthrough Therapy Designation in the United States.

The overall drisapersen clinical program comprises three double-blind, placebo-controlled studies (DEMANDII/DMD114117, DEMANDV/DMD114876 and DEMANDIII/DMD114044) and two long term open-label extension studies (DMD114673 and DEMAND IV/DMD114349). Over 300 patients have participated in clinical studies of drisapersen at more than 50 trial sites in 25 countries.

About exon skipping
The dystrophin gene is the largest gene in the body, consisting of 79 exons. Exons are small segments of genetic code which, via an intermediate step involving RNA, lead to the assembly of sections of protein. In DMD, when certain exons are mutated/deleted, the RNA cannot be processed past the fault. This prevents the remainder of the exons from being read, resulting in a non-functional dystrophin protein and the severe symptoms of DMD. RNA-based therapeutics, specifically antisense oligonucleotides inducing exon skipping, are currently in development for DMD. These antisense oligonucleotides skip an exon next to, or containing, the fault and thereby correct the RNA processing, enabling the production of a novel, largely functional dystrophin protein. Prosensa's exon skipping technology was licensed from Leiden University Medical Center.

Forward Looking Statement
This press release contains certain forward-looking statements. All statements, other than statements 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-looking statements. The words "anticipate," "believe," "estimate," "expect," "intend," "may," "plan," "predict," "project," "target," "potential," "will," "would," "could," "should," "continue," and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Forward-looking statements in this press release include statements around our lead exon-skipping compound, drisapersen and the regulatory review around this program. Actual results may differ materially from those projected or implied in such forward-looking statements. Such forward-looking information involves risks and uncertainties that could significantly affect expected results. These risks and uncertainties are discussed in the Company's SEC filings, including, but not limited to, the Company's Form 6-K's and the Company's Annual Report on Form 20-F. In addition, any forward-looking statements represent our views only as of today and should not be relied upon as representing our views as of any subsequent date. While we may elect to update these forward-looking statements at some point in the future, we specifically disclaim any obligation to do so, even if our views change.

Issued for and on behalf of Prosensa Holding N.V. by Instinctif Partners.

To contact the Prosensa team at Instinctif Partners, email

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Sue CharlesManaging Partner