Subjective sleepiness as evaluated with the Japanese version of the Epworth Sleepiness Scale (JESS) scores in unmedicated conditions and arousal index were nominally higher in the orexin mutation-positive patients (P = 0.049 and P = 0.046, respectively), suggesting that mutation-positive IH patients suffered more sleepiness and sleep instability similar to orexin-deficient narcolepsy type 1. The gene discussed is HCRT; the disease is isolated hemihyperplasia.