Molecular diagnostic tests to predict the risk of progressive multifocal leukoencephalopathy in natalizumab-treated multiple sclerosis patients

Natalizumab is a humanized monoclonal antibody against the alpha4 chain of the alpha4beta1 and alpha4beta7 integrin heterodimers used with high effectiveness in the treatment of multiple sclerosis. The use of this drug can unfortunately be associated with the onset of progressive multifocal leukoencephalopathy, a possibly fatal infection of the central nervous system, caused by polyomavirus JC. To understand and quantify the risk of developing PML is important for patients who are about to start therapy with natalizumab and for patients who already are under treatment with this drug. In this review we describe and critique molecular diagnostic tests proposed in the last years to assess the risk of PML.