SNP (rs2305795) of the P2RY11 gene is found to be related to narcolepsy with cataplexy (Narcolepsy type 1, NT1), which is an immune-related disease characterized by a significant loss of HCRT (hypocretin neuropeptide precursor; also known as orexin) neurons (Kornum et al. 2011). Here, HCRT is linked to narcolepsy-cataplexy syndrome.