Human longevity, however, is a complex phenotype that encompasses disease-specific risks as well as the individual rate of aging. The study of its genetic antecedents is challenging. The study of longevity may be affected by small genetic effect sizes, population stratification artifact, population heterogeneity, lack of sufficient numbers of long-lived study participants, and other problems (3, 4, 41). Therefore, to assess potential genetic contributions to human longevity from genes linked to IIS signaling, we chose a large, homogeneous, long-lived population of men well-characterized for aging phenotypes, and we performed a nested-case control study of 5 candidate longevity genes with links to the IIS pathway. These genes were chosen based on prior associations with aging phenotypes principally from gene knockout, transgenic, mutant, and other model organisms (3, 4, 14-17, 36, 42). Priority was given to genes involving insulin sensing and glucose (energy) homeostasis.

Five genes were investigated (ADIPOQ, FOXO1A, FOXO3A, SIRT1, and COQ7). Minor allele frequencies and other related genetic information for the cases and controls are presented in Table 2. However, only FOXO3A genotype was associated with longevity using an initial cut-off value of P=0.05. Further investigation comparing the genotype frequencies of FOXO3A3 between cases and controls revealed a highly significant difference P<0.00009 for the Pearson's exact χ2 statistic (Table 3). Five loci with 3 SNPs within each allele were tested (Table 2). Bonferroni adjustment for multiple comparisons resulted in a corrected p-value of 0.00135. Due to the high LD between the 3 SNPs of FOXO3A, we further investigated the FOXO3A3 SNP only (rs2802292). The OR for homozygous minor vs. homozygous major alleles for FOXO3A3 between the cases and controls was 2.75 (95% CI: 1.51-5.02, P=0.0007), and the OR for heterozygous vs. homozygous major alleles between the cases and controls was 1.91 (95% CI: 1.34-2.72, P<0.0003). These results suggest an(RS 2802292) Table 4: Difference in Health Status Between Genotype Groups at Baseline

Case-Control Status TT TG GG Average-Lived Phenotype* 223 (55%) 153 (38%) 26 (6%) Longevity Phenotype 81 (38%) 106 (50%) 26 (12%) P value for Pearson Exact test 0.000091 P value after Bonferroni adjustment 0.00135 Healthy at Baseline,* % Healthy at Baseline,* % P value for Trend Homo. Homo. Adj. for Major Heter. Minor Unadjusted Case-Control Stat FOXO3A1 57.41% 69.48% 75.51% 0.01% 0.065 FOXO3A2 57.37% 69.35% 77.08% 0.01% 0.035 FOXO3A3 57.89% 68.34% 75.00% 0.02% 0.097 *Number and percentage of subjects from n=402 "average-lived" decreased controls (mean attained age of 78.5 years). Number and percent of subjects from n=213 "long-lived" cases (mean attained age of 97.9 years). From the exact Pearson χ2 test comparing the genotype frequencies in the cases and controls.
*"Healthy" is defined as the absence of six major chronic diseases (CHD, stroke, cancer, PD, COPD, and treated type-2 diabetes; high physical function [can walk one-half mile] and high cognitive function [CASI score of 74]).

Table 7: Genotype Distribution by Maximum Attained Age

Age at Death (Years)* n MAF of FOXO3A3 

72-74 17 0.21 
75-79 277 0.25 
80-81 108 0.26 
95-99 185 0.37 
100-106 28 0.39 
TT TG GG P* 
Fasting Glucose, mg/dl Average-Lived 118.4 34.0 117.4 It 38.0 115.9 40.1 0.80 Long-Lived 108.3 20.7 109.1 23.7 110.5 24.1 0.73 Fasting Insulin, mIU/liter Average-Lived 23.7 81.2 30.4 Ib 91.9 13.2 It 5.9 0.004 Long-Lived 13.5 9.0 14.1 13.4 13.3 9.3 0.77 Log Fasting Insulin, mIU/liter Average-Lived 2.68 0.67 2.73 It=0.85,2=2=47=0=48= Long-Lived=2=45=55,=61,=44=52=99 HOMA IR Score Average-Lived=9=1,53=10,32,3=8 Long-Lived=3=7,28,4,3=6 All subjects (n=615) had metabolic profiles suggesting higher insulin sensitivity at younger ages with lower waist-to-hip ratio, lower glucose, insulin and HOMA values (Tables1 and5). Several phenotypes were associated with variation in FOXO3A genotype.

Surprisingly, there was no significant difference in diabetes prevalence between cases and controls.However,since the cases were more than a decade older than controls and diabetes tends to increase markedly with age,it is noteworthy that the prevalence of diabetes was not significantly different. In fact, both cases and controls had a high prevalence of diabetes (near 60%), despite relatively low BMI. Why type 2 diabetes tends to be more prevalent in Japanese at a relatively low BMI is not completely understood (50). However, there may be metabolic differences in Japanese (and some other Asians) with higher visceral fat in Asians at lower BMI than in whites and blacks (51, 52). Indeed, Japan national guidelines reflect such population differences and consider Japanese obese at a BMI of 25 (53). Other contributing factors to the high prevalence of diabetes in the HHP/HAAS cohort are that participants were tested for diabetes by several clinical methods and at several examinations making detection more likely.

Table 6: Prevalence of Aging-Related Phenotypes in Relation to FOXO3A3 Genotype

FOXO3A in Human Health, Aging, and Longevity