In line with Hayashi et al.’s [66] results, an earlier study by Fronczek et al., (2005) also observed no significant difference in orexin neurons in the hypothalami of seven PWS patients compared to well-matched control samples (matched for age, sex, post-mortem delay, fixation time and premorbid illness duration), suggesting orexin is not directly implicated in the hypersomnolence seen in PWS [63]. Here, HCRT is linked to Prader-Willi syndrome.