More than 17% of the ME/CFS patients had an unclassified antibody deficiency, being defined as recurrent or severe bacterial infection or autoimmune phenomena, and a deficiency of IgG, IgG subclass, IgM, IgA and/or specific antibodies, alone or in combination [19]. The gene discussed is CD40LG; the disease is myalgic encephalomeyelitis/chronic fatigue syndrome.