Understanding mutant forms of the virus

Mysterious mutants

Even if they are not the ones killing key brain cells, mutant JC polyomaviruses are up to some kind of no good. They are only found in the brains of people who become sick with progressive multifocal leukoencephalopathy. Credit: Ursula Neu/Tübingen University

A new study shows that common mutant forms of the deadly JC polyomavirus are not responsible for the pathogen’s main attack, which causes a brain-damaging disease in immunocompromised patients called progressive multifocal leukoencephalopathy. But that finding raises the ominous question of what the mutants might be up to instead.