CDON and myalgic encephalomeyelitis/chronic fatigue syndrome: Three of the genetic variants that were significant in the Pain Questionnaire analysis—located in genes SLC6A11, SULF2 and CDON—were identified in communities of ME/CFS patients more likely (p = 0.003, Additional file 1: Table S9) to report the occurrence of illness and psychosocial factors (injury, bereavement, stress) in the last 3–8 years.