An Update on Kleine-Levin Syndrome.

Purpose of Review: Kleine-Levin syndrome (KLS) is a rare relapsing-remitting sleep disorder distinguished by recurrent periods of severe hypersomnia accompanied by cognitive, mood, and behavioral changes. This review focuses mainly on the most recent developments and articles concerning this illness in the preceding five years while attempting to provide a basic overview of KLS. Recent Findings: Genetic links were reported in some patients with KLS, like variation in TRANK1 in a worldwide case-control genome-wide association in patients with KLS, in addition to several uncommon variations in the LMOD3 gene, some of which are likely to be pathogenic, discovered by linkage analysis and exome sequencing in a sizable Saudi Arabian family with KLS and a European cohort of KLS patients. Additionally, recent data indicate that the amplitude of the circadian active/rest cycles significantly decreased during hypersomnia attacks, but during asymptomatic periods, it did not differ significantly from the controls. Moreover, patients with KLS are at a higher risk of developing emerging psychiatric disorders during follow-up. Recent data also points to possible discoveries of diagnostic-potential dysregulated proteomic patterns in KLS. Finally, new data suggest that functional imaging studies are often abnormal in KLS both during and between episodes. Summary: KLS is an uncommon, severe, and uniform illness. When it comes to the diagnosis and treatment of KLS, these characteristics offer both opportunities and challenges. Over the past five years, some promising work has appeared in genetics, functional imaging, and biomarker identification; nevertheless, these areas still need more focus to advance the detection and treatment of patients suffering from KLS.