BCR and myalgic encephalomeyelitis/chronic fatigue syndrome: BCR repertoire sequencing in ME/CFS and healthy controls (HCs) previously identified increased use of several Immunoglobulin Heavy Chain V (IGHV) gene segments in ME/CFS patients: IGHV-3-30 and IGHV3-30-3 gene usage was elevated in ME/CFS, particularly in patients who reported an infectious onset to their illness (19).