The co-existence of ME/CFS and gastrointestinal symptoms is well documented [115] with one study reporting that 92% of ME/CFS patients have co-existent irritable bowel syndrome (IBS) [116] and with studies of the immunological relationship between the two conditions showing increased mucosal and systemic levels of pro-inflammatory cytokines IL-6, IL-8, IL-1β and TNFα [117,118]. This evidence concerns the gene TNF and irritable bowel syndrome.