Of these studies, 5 concerned the occurrence of early-onset toxicities (40, 42, 43, 48, 67), including severe cases of leukopenia, neutropenia, lymphopenia and thrombocytopenia that occurred in four female and one male patients, aged <58 years, with a medication history that included at least IFN and/or natalizumab for all of them. The gene discussed is IFNA1; the disease is Decreased total leukocyte count.