Gilenya just recently has been classified as a possible cause for PML . But by comparison to tecfidera or some of the monoclonal antibodies AKA mabs , the chances are slim . Things to be more concerned about would be heart rate , liver function , and white blood cell count . Obviously talk to your doctor . Especially if you have heart problems . I ' ve been having complications with it so I have to take a blood test every month now . Don ' t let that discourage you because I have recently been diagnosed with Gilbert ' s Disease . It ' s believed that that may be causing my liver enzymes to jump around . I ' ve had very aggressive in multiple sclerosis as well . I was previously on interferon . Gilenya is very very efficient . Edit changed are to or