CTLA4 and myalgic encephalomeyelitis/chronic fatigue syndrome: Specific single nucleotide polymorphisms (SNPs), such as PTPN22 rs2476601 and CTLA4 rs3087243, are associated with infection-triggered CFS/ME, while other SNPs, such as IRF5 rs3807306 and TNF rs1799724, have decreased allele frequencies in CFS/ME patients who do not have infection-triggered onset [38].