Genetic Variations in Renin-Angiotensin-Aldosterone System (RAAS) Genes Could Contribute to High Altitude Pulmonary Edema: Review

Background: At High Altitude (HA) (elevation >2500m), inevitable hypobaric hypoxia leads to development of symptoms associated with low oxygen pressure in many non acclimatized sojourners which includes severe forms of altitude mountain sickness (AMS) such as high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). These syndromes are reportedly less common in high altitude native population than in lowlanders which can be attributed to genetic adaptations that have taken place over generations. Methods: Numerous genetic studies have been associated with hypoxic adaptation and susceptibility to high altitude conditions. An increased pulmonary arterial pressure (PAP) and fluid loss has been observed in all forms of AMS with varied intensity. Since renin-angiotensin-aldosterone system (RAAS) has a critical function of maintaining homeostasis in closed circulatory system, the polymorphisms occurring in the genes of RAAS pathway could likely be contributing towards acclimatization/mal-adaptation to high altitude maladies. In view of above, this review has been compiled to associate the genetic variations in RAAS with adaptation/acclimatization to high altitude conditions. Results: Studies conducted so far relate allele frequencies of polymorphic loci in genes encoding components of RAAS pathway such as angiotensinogen (AGT), angiotensin converting enzyme (ACE), angiotensin receptors (AT1) and aldosterone synthase (CYP11B2) and associate them with hypertension, regulation of blood pressure and maintenance of osmotic balance in the body. Conclusions: In this review, various studies have been put together comprehensively indicating the involvement of genetic variants of RAAS genes in resistance or sensitivity of an individual towards development of HAPE.