High-Altitude Illness Decoded: Mechanisms, Genetics, and New Treatments

High altitude exposure above 2500 m poses serious health risks to both permanent residents and visitors. With approximately 80 million people living permanently at high altitudes and over one million visitors annually, understanding altitude-related illnesses has major global health significance. This comprehensive narrative review synthesizes decades of research on the full spectrum of high-altitude diseases, with particular emphasis on recently uncovered pathophysiological mechanisms and genetic factors.

The review distinguishes between acute altitude illnesses—AMS, HACE, and HAPE—which arise within hours to five days from inadequate physiological adaptation, and chronic conditions—CMS and HAPH—which develop over years from pathological overadaptation. AMS prevalence rises dramatically with altitude, from 12% at 2000 m to nearly universal occurrence above 4000 m. HACE affects 0.28–1% of people at ~4000 m, while HAPE incidence increases sharply with rapid ascent (up to 15.5% at 5500 m with fast ascent). Chronic conditions show strong altitudinal gradients: CMS prevalence on the Qinghai-Tibet Plateau rises from 1.05% at lower elevations to 11.83% above 4000 m.

Pathophysiologically, the review details how hypobaric hypoxia triggers cascading responses across multiple organ systems. In the brain, increased cerebral blood volume, neurohormonal activation, and decreased Na⁺/K⁺ ATPase activity contribute to capillary leakage and cytotoxic edema central to HACE. HAPE is driven by exaggerated hypoxic pulmonary vasoconstriction, inflammation, and impaired alveolar fluid clearance. CMS arises from hypoventilation and excessive 2,3-DPG accumulation, driving pathological EPO overproduction and erythrocytosis (Hb ≥19 g/dL in women, ≥21 g/dL in men). HAPH progresses through pulmonary arterial smooth muscle cell (PASMC) contraction-mediated hypoxic pulmonary vasoconstriction (HPV) and subsequent hypoxic pulmonary vascular remodeling (HPVR), culminating in right ventricular hypertrophy and heart failure.

A major strength of this review is its detailed treatment of genetic susceptibility. Population differences—notably the lower CMS prevalence among Tibetans versus Andeans—point to evolutionary adaptations encoded in genes such as EPAS1 (HIF-2α), EGLN1, and others involved in oxygen sensing. This genetic architecture partly explains why Tibetans maintain lower hemoglobin levels despite multigenerational high-altitude residence. The review also covers risk factors including preexisting cardiopulmonary disease, patent foramen ovale (PFO), sleep-disordered breathing, obesity, and ascent rate.

Regarding management, the review covers pharmacological options (acetazolamide, dexamethasone, nifedipine, phosphodiesterase inhibitors), behavioral strategies (staged ascent, preacclimatization), and supplemental oxygen. Importantly, it highlights growing evidence for traditional Tibetan medicines as promising preventive and therapeutic agents, though rigorous clinical trial data remain limited. The authors acknowledge that despite extensive research, exact disease mechanisms remain incompletely understood and management options are still constrained, calling for further mechanistic and translational investigation.