Additionally, polymorphisms in various other genes (Table 2), such as the purinergic receptor (P2Y11) [38], C-C motif chemokine receptors 1 and 3 (CCR1-CCR3) [39], cathepsin H (CTSH) [40], tumor necrosis factor superfamily member 4 (TNFSF4) [40], choline kinase beta (CHKB), and carnitine palmitoyltransferase 1B (CPT1B) [41,42], have also been associated with an increased susceptibility to narcolepsy. Here, CCR3 is linked to narcolepsy.