CAMBRIDGE, Mass. ( TheStreet) -- European regulators confirmed that 24 multiple sclerosis patients treated with Tysabri have contracted a serious brain infection. Four of those patients have died, according to the investment bank UBS. The new disclosure concerning the link between Tysabri treatment and progressive multifocal leukoencephalopathy, or PML, pushed shares of Biogen Idec ( BIIB - Get Report) and Elan ( ELN), makers of Tysabri, lower in Thursday trading. Last week, European regulators launched a new safety review of Tysabri after it was disclosed that 23 multiple sclerosis patients treated with Tysabri had contracted PML since the drug was relaunched in 2006. The number of PML cases tied to Tysabri was much higher than investors had previously known. The 24 cases of Tysabri-linked PML and four patient deaths was disclosed Thursday in an email sent by European regulators to UBS drug analyst Martin Wales, who was seeking more information about the link between Tysabri and PML cases. The email has been circulated across Wall Street trading desks this morning. A copy of the email, obtained by TheStreet, states: "We can confirm that to date, 24 confirmed cases of PML have been reported worldwide since Tysabri has been on the marked in the EU in 2006.
Fourteen of these ocurred in the EU, 8 in the US and 2 in Switzerland. Four patients died. Most of the cases were reported in patients who have had 24 or more infusions of Tysabri."
Biogen Idec shares were down 2% to $42.71 while Elan shares were off 4% to $4.81.
But the FDA said it was not comfortable with Intermezzo's safety profile, particularly the risk that people might suffer lingering effects from the drug after they woke up. In particular, regulators want Transcept to show that Intermezzo has no negative effect on next-day driving ability, the company said. Transcept said it may have to conduct one or more additional safety studies to provide FDA with the data it needs to approve Intermezzo. Transcept shares closed Wednesday at $11.47 but appear to be trading sharply lower in pre-market trading Thursday. -- Reported by Adam Feuerstein in Boston