SLC15A4 and myalgic encephalomeyelitis/chronic fatigue syndrome: In both Severe and Fatigue Dominant long COVID populations, we identified SNPs mapping to the genes ATP9A, INSR, CLOCK, SLC15A4 and GPC5. All of these genetic variants were found in a higher proportion of the Fatigue Dominant and Severe long COVID populations than in the ME/CFS case group.