Elevated intrathecal IgM synthesis, but not other immunoglobulins, has been suggested to predict a worse disease evolution since the early MS stages, being associated in patients with a more disability progression and with a more aggressive form of the disease (Walsh and Tourtellotte, 1986; Villar et al., 2002, 2003; Cepok et al., 2006; Durante et al., 2012; Beltrán et al., 2014; Frau et al., 2018). The gene discussed is CD40LG; the disease is myeloid sarcoma.