HCRT and isolated hemihyperplasia: In addition, unlike NT1, for which cerebrospinal fluid hypocretin (also known as orexin) deficiency is a reliable biomarker reflecting disease pathology (Huang et al., 2018), no definitive biomarkers have been established for IH, though several mechanisms have been proposed such as a positive allosteric modulator at the GABAA receptor (Rye et al., 2012).