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There was a good investor analysis of the GSK/Prosensa results on various investor sites, which basically were the results were not as good as expected as far as strength improvement goes (not statistically significant). The results were blamed on the participants having difficulty tolerating the dosing levels, which had to be kept fairly low. Even at the low dosing levels, there were side effects as well.
However I did hear on the call that the results did see clinical benefit and lowered cpk counts, that seem to indicate the medicine was working. So for researchers this isn't all bad news - just means that more study is needed to figure out how to distribute the medicine better throughout the body and reduce the side effects, so that the dosing can be higher.
In contrast, Sarepta has been doing really well with their delivery and results of their medicines. Look at GSK stock vs. Sarepta stock. This is how much faith investors have in Sarepta at the moment.