The curve differences (n = 15 WT and n = 15 compound hKO, chKO) are statistically significant by log-rank (Mantel-Cox) and Gehan-Breslow-Wilcoxon tests. Healthy life span is measured by the total number of days until spontaneous death or the development of morbidities that require euthanasia in chronic hypoxia. The depicted curve includes all mice that died spontaneously or were euthanized due to morbidity (e.g., all events described in Table 1). The curve excludes points for 4 WT, which include M197 and 3 mice from experiment 3 (Table 1), and 8 hKO, which include M145, M515, M536, and 5 mice from experiment 3 (Table 1). These mice are censored since they did not complete the life span endpoints.