An integrative review on the orexin system and hypothalamic dysfunction in myalgic encephalomyelitis/chronic fatigue syndrome: implications for precision medicine

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating multisystem disorder affecting an estimated 0.4% to 2.5% of community populations. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and marked metabolic heterogeneity underscore its complex pathophysiology. The hypothalamic peptides hypocretin-1 and -2 (also known as orexin-A and orexin-B), synthesized by neurons in the lateral hypothalamus, regulate sleep-wake cycles, arousal, autonomic function, and energy homeostasis. This integrative review aimed to synthesize current evidence on hypothalamic orexinergic dysfunction in ME/CFS and assess its potential as a biomarker framework for stratification in precision medicine. The review followed Whittemore and Knafl’s five-stage methodology. Comprehensive searches were conducted across PubMed, Scopus, Web of Science, and OpenAlex up to April 2025, supplemented by manual screening of reference lists. Data extraction and synthesis were performed using constant comparison techniques to integrate quantitative outcomes with theoretical insights. Twenty-seven studies met the inclusion criteria, consistently reporting reduced orexin-A levels in individuals with ME/CFS and variable orexin-B responses indicative of biomarker potential. Neuroendocrine findings, including alterations in cortisol and adrenocorticotropic hormone levels, along with inflammatory profiles, confirmed the involvement of neuroimmune interactions. Multi-omics analyses further delineated distinct patient subtypes characterized by unique molecular signatures. Hypothalamic orexinergic dysfunction emerges as a central feature of ME/CFS, with orexin-B representing a promising candidate biomarker. The integration of orexin profiling with multi-omics data and machine learning strategies provides a viable pathway towards precision-medicine interventions for this heterogeneous condition.