They say that there have been no new cases of progressive multifocal leukoencephalopathy (PML), the brain disorder.

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Though it is highly effective, some patients developed a rare and fatal infection known as progressive multifocal leukoencephalopathy.

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There have been other cases, too, of patents taking Tysabri coming down with the rare and usually fatal brain disease called progressive multifocal leukoencephalopathy (PML).

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In a rare condition called progressive multifocal leukoencephalopathy, a virus stripped the lining from their nerves in their brain much more quickly than MS would have.

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