TPH2 and myalgic encephalomeyelitis/chronic fatigue syndrome: Sequence variations in some of these genes were reported to be associated with CFS (NR3C1: Rajeevan et al. [60] and HTR2A: Smith et al. [27]) or associated with some of the CFS subtypes identified by latent class analyses (MAOA, MAOB, TPH2, and NR3C1: Smith et al. [61]) or association with allostatic load, a construct that describes cumulative physiological effects of adaptation in response to stress (ACE: Smith et al. [62]).