By subdividing the ME/CFS group based on the severity of symptoms (1, severe; 2, moderate; and 3, mild), statistically significant differences were observed between the CTR group and ME/CFS-2 and ME/CFS-3 subgroups for IL-17A (p < 0.0001 and p = 0.0043, respectively), IL-2 (p < 0.0001 and p = 0.0004), IL-21 (p < 0.0001 and p = 0.0005), and IL-23 (p = 0.0013 and p = 0.0156). This evidence concerns the gene IL17A and myalgic encephalomeyelitis/chronic fatigue syndrome.