Is Idiopathic Hypersomnia a Circadian Rhythm Disorder?

PURPOSE OF REVIEW: The pathophysiology of idiopathic hypersomnia remains unclear, but some of its clinical features suggest the possibility of circadian dysfunction. This review will provide an overview of recent studies of circadian biology that have begun to elucidate the potential role of circadian rhythm dysfunction in idiopathic hypersomnia. RECENT FINDINGS: Clinically, people with idiopathic hypersomnia tend to have both a late chronotype and prominent sleep inertia or sleep drunkenness. Melatonin and cortisol profiles in people with IH confirm this tendency toward phase delay. More recently, it has been suggested that the night phase as defined by melatonin profile or period length as defined by BMA1 in dermal fibroblasts may also be prolonged in people with IH. Additionally, amplitude of melatonin rhythm and circadian gene expression, particularly BMAL1, PER1, and PER2, may be impaired in this disease. SUMMARY: Clinical features, melatonin profiles, and circadian gene expression all suggest abnormalities of the circadian system may be a contributor to the pathogenesis of IH.