NT2, formerly named narcolepsy without cataplexy (American Academy of Sleep Medicine 2005), is characterised by (i) EDS present for at least 3 months, (ii) mSL ≤ 8 min and ≥ 2 SOREMPs on the MSLT, with a SOREMP on the preceding nocturnal PSG that may replace one of the SOREMPs on the MSLT, (iii) absence of cataplexy, (iv) CSF‐HCRT1 > 110 pg/mL (or > 1/3 of normal values), if measured, and (v) hypersomnolence and/or MSLT findings are not better explained by other causes (American Academy of Sleep Medicine 2023). This evidence concerns the gene HCRT and Cataplexy.