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Leiden University Medical Center and Prosensa B.V. Announce New England Journal of Medicine Publication of First Successful Clinical Study with RNA-based Therapeutic PRO051 in Duchenne Muscular Dystrophy

By December 27, 2007November 27th, 2018News
Novel RNA-based therapeutic PRO051 to enter Phase I/II clinical trials in DMD

Leiden, the Netherlands, December 27, 2007. Leiden University Medical Center (LUMC) and
Biotech Company Prosensa announced today in the New England Journal of Medicine (van
Deutekom et al.) positive results from the first ever clinical study with RNA-based therapeutic
PRO051 in four patients with Duchenne Muscular Dystrophy (DMD), in which PRO051 has
restored dystrophin expression in the treated muscle fibers of all four patients tested.

In this study, DMD patients between 10 and 13 years of age received a single injection of
PRO051 (a 2-’O-methyl antisense oligonucleotide) in a small area of a muscle in the lower leg. In
a biopsy taken four weeks later, novel dystrophin expression was observed in the vast majority of
muscle fibers with protein levels that are expected to be clinically relevant. This pilot study is the
first ever with an RNA-based therapeutic agent for DMD and is an important step towards
treatment of this devastating disease, for which as yet no therapy is available. Following this first
clinical proof-of-mechanism, Prosensa has started the preparations for a phase I/II clinical study
to explore the effects and safety of PRO051 after repeated systemic injections.

Gerard Platenburg, Prosensa’s CEO, commented: “This first clinical study demonstrates that
PRO051, an RNA-Therapeutic based on our proprietary exon skipping technology, was able to
correct this genetic error in locally injected muscle tissue of Duchenne Muscular Dystrophy
patients. We are excited to have demonstrated clinical proof-of-mechanism and will be
progressing PRO051 into systemic Phase I/II trials in order to assess the broader benefits
available to patients. RNA-based therapeutics hold great promise as an approach to create a
whole new class of innovative medicines and we are well positioned to exploit this opportunity.”
Professor Gert-Jan van Ommen, together with his colleagues Dr. Judith van Deutekom and Dr.
Jan Verschuuren responsible for the research at the LUMC commented: “After eight years of
preparatory work we were greatly rewarded by this wide-spread expression of dystrophin
throughout the muscle biopsies” and “The robust expression in all four patients with different
mutations after a single injection points to a solid effect. The results form an excellent starting
point for systemic treatment trials”.

Professor Eric Hoffman, one of the pioneers who identified dystrophin as the missing protein in
DMD in 1987, remarked in a commenting editorial that “the paper by Van Deutekom et al. might
herald the dawn of personalized molecular medicine”.

Elizabeth Vroom, President of the United Parent Projects Muscular Dystrophy emphasized the
enthusiasm amongst the patient community: “Duchenne parents all over the world are incredibly
excited about the extremely promising results of the first human exon-skipping trial, which took
place in the Netherlands. We greatly appreciate all the work the research team has put into this
trial and are desperately hoping for positive results in the next stage also.” About DMD and Exon skipping
Duchenne muscular dystrophy is a severely debilitating childhood neuromuscular disease that
affects 1 in 3500 newborn boys. The young patients suffer from progressive loss of muscle
strength due to the absence of the protein dystrophin, making them wheelchair bound before the
age of 12 and most die in early adulthood due to respiratory and cardiac failure. Today, there is
no treatment to prevent the eventual fatal outcome. The disease is caused by mutations in the
DMD gene, resulting in the absence of the dystrophin protein, which is crucial for the integrity of
muscle fiber membranes.

RNA-based therapeutics, specifically antisense oligonucleotides inducing exon skipping, are
currently the most promising therapy for Duchenne Muscular Dystrophy. More specifically,
antisense oligonucleotides have the capacity to skip an exon and thereby correct the reading
frame of DMD transcripts resulting in the synthesis of a largely functional dystrophin protein.
Different mutations in the gene require different oligonucleotide drugs. The PRO051, the first of
its kind, will be suitable for 13% of all DMD patients, because it can treat a cluster of mutations.

About LUMC

Leiden University Medical Centre (LUMC) aims to play a leading role, nationally and
internationally, in the further improvement of health care quality. LUMC’s key tasks are research,
patient care, and academic and post-academic medical education. It performs 11,500 daytime
treatments and 19,000 hospital admissions yearly. It has 800 beds and employs 8700 people.
For more information please visit

About Prosensa

Prosensa is a Dutch biopharmaceutical company dedicated to the development of RNA-based
therapeutics targeting diseases with unmet medical needs, in particular neuromuscular disorders.
Prosensa’s drug development is based upon a unique and proprietary technology platform
involving ‘exon skipping’, enabling correction of mutated RNA. This ability to modulate genes
selectively through RNA-based therapeutics could provide a new way to treat a wide range of
human diseases. The company has a leadership position in fundamental patents, technology,
and know-how relating to RNA-based approaches and exon skipping. Prosensa’s lead
compounds for DMD are currently in clinical phase I/II development and the company has
received orphan drug designation both in Europe and the US. For more information on Prosensa,
please visit

For more information, please contact:

For Prosensa: Gerard Platenburg, CEO
T: +3171 5274202
M: +3165 3439090
For LUMC: Professor Gert-Jan B van Ommen, Head Dept of Human Genetics
T: +3171 526 9401
M: +31 622 209 265
For Duchenne Parent Project: Elizabeth Vroom, President
T: +31 206275062
M: +31 621565721
E: dpp@euronet.nlFor PR: Citigate Dewe Rogerson: Yvonne Alexander/ David Dible
T: +44 20 7282 9571
M: +44 7866 610682
E: /