It is thought that SLX4 recruits MUS81 and XPF to these sites and that recruitment requires the SUMO-interacting motifs of SLX4 (SIMs) (Guervilly et al. 2015; Ouyang et al. 2015), suggesting that SUMOylation of SLX4 may play a role in CFS expression by the SMX complex. This evidence concerns the gene SLX4 and myalgic encephalomeyelitis/chronic fatigue syndrome.