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Muscular dystrophy genetic therapy falls short in major trial

23 September 2013
Appeared in BioNews 723

A highly anticipated experimental treatment for the genetic condition Duchenne muscular dystrophy (DMD) has failed in a key test of its effectiveness in a critical phase III clinical trial.

The therapy, which relies on a genetic technique called 'exon skipping', was given to 186 patients for nearly a year. Those treated with the drug, called drisapersen, did not see a statistically significant improvement in the distance they could walk in six minutes compared with patients given placebo.

Robert Meadowcroft, chief executive officer of the Muscular Dystrophy Campaign in the UK, said the initial results of the trial would come as a 'heavy blow for the families of children with DMD'.

He added, however, that 'there are other exon-skipping projects underway, and alternative "chemistries" [different exon-skipping molecules] have shown us some encouraging results'.

DMD is the most common form of muscular dystrophy, affecting up to one in 3,500 live male births. It is a severe muscle-wasting disease; most patients require a wheelchair by the age of 12 and average life expectancy is only 27.

The disorder is caused by mutations in the DMD gene that prevent proper expression of the protein dystrophin. Certain exons, which are the parts of DNA that code for sections of protein, are mutated or deleted. These exon faults make the gene unreadable and the result is a completely non-functional protein.

Exon skipping introduces a 'molecular patch' over an exon to make the gene readable again, allowing production of a shorter from of dystrophin, but one thought to be more functional than the untreated version.

DMD is currently untreatable and considerable hope was pinned on drisapersen, the first exon-skipping therapy to reach clinical trials. In June this year, the US Food and Drug Administration awarded the drug 'breakthrough therapy' status, in order to help speed its development.

In the trial, the patients who received drisapersen were able to walk on average ten metres further than boys given placebo. But statistical analysis could not confirm whether this improvement was a genuine effect of the drug or could be put down to chance.

Hans Schikan, chief executive officer of Prosensa, the biotech company developing drisapersen in partnership with GlaxoSmithKline (GSK), said: 'While we are disappointed that this study did not meet its primary endpoint, we remain committed to the overall programme and will continue to work closely with GSK'.

Speaking on behalf of GSK, Dr Carlo Russo, the company's head of rare diseases research and development, added: 'We are committed to evaluating the outcome of this study in the context of the overall development programme with experts in the field, and we expect such evaluation to help inform our next steps for drisapersen. It is our hope that progress will be made in an effort to help boys with DMD'.

GSK and Prosensa Announce Primary Endpoint Not Met in Phase III Study of Drisapersen in Patients With Duchenne Muscular Dystrophy
Prosensa (press release) |  20 September 2013
GSK, Prosensa muscular dystrophy drug misses study goal
Reuters |  20 September 2013
Muscular dystrophy drug from GlaxoSmithKline, Prosensa fails PhIII
Fierce Biotech |  20 September 2013
Prosensa and GlaxoSmithKline announce results of exon skipping trial
Muscular Dystrophy Campaign (press release) |  20 September 2013
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