Further evidence has accumulated supporting the causal role of hypocretin deficiency in the origin of NC [8], however, participation of hypocretin signaling in other forms of central hypersomnia including narcolepsy without cataplexy (NWC) or idiopathic hypersomnia (HI) is less understood, although a partial hypocretin deficiency is possible in the former condition [9], [10]. This evidence concerns the gene HCRT and idiopathic hypersomnia.