Update and correction: Prosensa says some of the statements made by JMP Securities analyst Liisa Bayko in her research note were factually incorrect. The story has been updated where appropriate. NEW YORK ( TheStreet) -- Duchenne muscular dystrophy (DMD) patients treated with Sarepta Therapeutics' ( SRPT) eteplirsen continue to do well on therapy, according to the company's chief medical officer speaking at the Action Duchenne meeting held this weekend in London. JMP Securities analyst Liisa Bayko was in London attending the meeting, where Sarepta's chief medical officer Dr. Ed Kaye discussed results from the eteplirsen phase II study. In a note to clients this morning, Bayko writes: The next catalyst for Sarepta will be 62-week data, which we believe may be presented in January in San Francisco, and Dr. Kaye noted that the patients continue to do well on therapy with no decline in function nor missed infusions or discontinuations. Bayko also learned that GlaxoSmithKline ( GSK) and Prosensa won't release results from controlled studies of their competing DMD drug drisapersen until the third quarter 2013. Again, Bayko: GSK disclosed that it is committed to a full development program and will not release data from the Phase 2 placebo controlled study until 3Q13 at the earliest, and it is targeting 2014-15 for approval. In our view, this removes some risk from Sarepta -- in the event that it is enrolling a Phase 3 program in 2014, drisapersen will not yet be commercially available and competing for patients. Glaxo and Prosensa's larger drisapersen phase III study is also ongoing with data not expected until the fourth quarter 2013, according to Bayko's account of Glaxo's presentation at the Action Duchenne meeting. More from Bayko's note on drisapersen: GSK provided an update on the ongoing long-term extension (LTE) study from the original cohort of 12 patients. Whereas the study originally evaluated weekly intramuscular dosing, the LTE utilizes an eight weeks on/four-weeks off schedule to alleviate key side effects, including proteinura (observed in 100% of the boys including increased urinary alpha 1 microglobin, which is a marker for proximal tubule kidney dysfunction) thrombocytopenia (observed in 1/3 of the boys) and difficult injection site reactions (ISRs) from the intramuscular injection (separately, concerns were raised about a potential un-blinding effect). Dr.
Padraig Wright from GSK relayed that the drug holiday seems to be helping and that no patient has discontinued this or any other global study, which speaks to the commitment of the DMD community and the potential benefit provided by drisapersen. Drisapersen is administered via subcutaneous injection, not intramuscularly, according to Prosensa. On eteplirsen: Importantly, we learned that nNOS, an important marker in muscle cells, was reconstructed, which further validates the drug candidate. Eteplirsen is cleared unmetabolized via the kidney and shows no signs of toxicity. Moreover, the intravenous delivery seems to be associated with less severe injection site reactions than drisapersen. No patient has yet to miss an infusion which speaks to the dedication, as well as the benefit of the compound. On the legal action between Glaxo and Sarepta regarding patents for exon 51-skipping drugs: On legal grounds, Sarepta continues to be blocked from engaging in clinical studies for exon 51 in the UK given GSK's patent win, though other European countries may be more flexible. While Sarepta has offered a royalty, GSK seems unwilling to budge. We also learned from Prosensa that they are pursuing legal action in the U.S. as well. That being said, exons beyond 51 and 46 are free and clear both domestically and abroad. Moreover, we believe that ultimately the law will side with patients -- should Sarepta's chemistry advantage continue to generate key safety benefits, we think it would be unconscionable to block patient access, particularly given these matters can usually be settled with money. Our review of the literature suggests that royalties for drug patents have historically hovered around 5%. Drisapersen's European patents are held by Prosensa, not Glaxo. Prosensa's European patents do not block Sarepta from conducting clinical trials but do prevent the company from developing a DMD drug based on the skipping of exon 51 in the DMD gene, according to Prosensa. Prosensa is not pursuing legal action against Sarepta in the U.S. Sarepta shares were up 10% to $25.06 in Monday trading. -- Reported by Adam Feuerstein in Boston. Follow @AdamFeuerstein