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Thomspon Julian, James Raitt, Lynn Hutchings, Fotios Drenos, Eirik Bjargo, Are Loset, Mike Grocott, and Hugh Montgomery, for the Caudwell Xtreme Everest Research Group. Angiotensin-converting enzyme genotype and successful ascent to extreme high altitude. High Alt. Med. Biol.8278–285, 2007.—Interindividual variation in acclimatization to altitude suggests a genetic component, and several candidate genes have been proposed. One such candidate is a polymorphism in the angiotensin converting enzyme (ACE) gene, where the insertion (I-allele), rather than the deletion (D-allele), of a 287 base pair sequence has been associated with lower circulating and tissue ACE activity and has a greater than normal frequency among elite endurance athletes and, in a single study, among elite high altitude mountaineers. We tested the hypothesis that the I-allele is associated with successful ascent to the extreme high altitude of 8000 m. 141 mountaineers who had participated in expeditions attempting to climb an 8000-m peak completed a questionnaire and provided a buccal swab for ACE ID genotyping. ACE genotype was determined in 139 mountaineers. ACE genotype distribution differed significantly between those who had successfully climbed beyond 8000 m and those who had not (p 0.003), with a relative overrepresentation of the I-allele among the successful group (0.55 vs. 0.36 in successful vs. unsuccessful, respectively). The I-allele was associated with increased maximum altitudes achieved 8079 ± 947 m for DDs, 8107 ± 653 m for IDs, and 8559 ± 565 m for IIs (p 0.007). There was no statistical difference in ACE genotype frequency between those who climbed to over 8000 m using supplementary oxygen and those who did not (p 0.267). This study demonstrates an association between the ACE I-allele and successful ascent to over 8000 m. [ABSTRACT FROM AUTHOR]