AKT1 was evaluated as a longevity-associated gene in Danish and German nonagenarians. Along with APOE and FOXO3, AKT1 has been suggested as a consistent longevity gene. Variants in AKT1 were found to be associated with human lifespan in two earlier studies. The aim of this study was to replicate the previously identified variant rs3803304 and analyze six additional AKT1 single-nucleotide polymorphisms to capture more of the common variation in the gene. The study population included 2996 long-lived individuals and 1840 younger controls of Danish and German ancestry. None of the seven SNPs tested were significantly associated with longevity in either a case-control or a longitudinal setting, although a nominal indication of a disadvantageous effect of rs3803304 was found in a restricted group of Danish centenarian men. Overall, the results do not support AKT1 as a universal longevity-associated gene. 

Approximately 25% of variation in human lifespan is attributable to genetic factors; however, polymorphisms in only a few candidate genes have so far been consistently found to be associated with longevity. The first candidate gene discovered is the apolipoprotein E (APOE) gene, which has repeatedly been reported as an age-related mortality factor in numerous populations. The forkhead box O3 (FOXO3) gene is another well-established candidate that encodes a transcription factor involved in the insulin/insulin-like growth factor 1 (IGF1) pathway. The insulin/IGF1 pathway has repeatedly been implicated in longevity in various model organisms, as well as in humans, where the FOXO3 association has been demonstrated in diverse populations of ethnic origin.

AKT1 is part of the insulin/IGF1 pathway and has been put forward as a third consistent longevity gene. Single-nucleotide polymorphisms (SNPs) in this gene have been associated with longevity in two studies. Pawlikowska et al. described the variant rs3803304 as influencing human lifespan in three different cohorts consisting of participants from the Study of Osteoporotic Fractures and the Cardiovascular Health Study, as well as Ashkenazi Jewish Centenarians, whereas the SNP rs2498804 was detected in a recent GWAS of Dutch nonagenarians from the Leiden Longevity Study.

In the Danish study population, genotyping of the candidate SNP rs3803304 was performed in all 1383 participants, of which 190 individuals (women proportion of 80%) lived to be at least 100 years of age, whereas genotype information on the six additional SNPs was available for 1089 individuals as previously described. A total of 143 of the 1089 individuals (women proportion of 79%) lived to be at least 100 years of age. In the German study population, genotyping of rs3803304, rs2494731, rs2494732, rs2498796, rs2494738 and rs1130214 was performed. As rs3803304 was previously found to be associated with longevity, it was investigated more thoroughly using a genotypic, dominant and recessive model. No significant associations were found with any of the models applied (data not shown).

The study approvals were received from the Danish National Committee on Biomedical Research Ethics and the Ethics Committee of the University Hospital Schleswig-Holstein, respectively.The following text has been proofread and corrected:

Performed using pre-designed TaqMan SNP genotyping assays (Applied Biosystems, Pleasanton, CA, USA), the SNP rs2494748 could not be genotyped in the German population due to technical difficulties. To scrutinize potential effects of variation in AKT1 on extreme survival, the analysis was restricted to centenarians only (Table 3), resulting in the ability to detect effects of size OR1.25 (for rs2494738, OR1.4) in the combined study population with a power of at least 80%. One nominally significant indication (P0.03) of a disadvantageous effect of rs3803304 on longevity was found in Danish men, and this indication was supported when applying genotypic and dominant models (P0.02 and 0.01, respectively). Genotyping of rs2494731, rs2494732, rs2498796, rs2494738, rs2494748, and rs1130214 in the Danish study population was part of a previous study performed using the Illumina GoldenGate Technology (Illumina Inc., San Diego, CA, USA) as described by Soerensen et al.13.

Statistical analysis: In addition to applying a cross-sectional approach, the effects of the seven SNPs on survival during old age were investigated in the Danish 1905 Birth Cohort. Regardless of the genetic model applied, no associations with survival during the follow-up of 412 years were found. Restriction of analysis to include centenarians only did not change this result (data not shown). All analyses were carried out using the statistical software Stata (Stata version 11.2; Stata Corporation, College Station, TX, USA). Logistic regression was used to assess the association between genotype and longevity with a dose of minor allele coded as 0, 1, and 2. An additive model was applied to all of the seven AKT1 SNPs; however, for rs3803304, the potential association with longevity was further explored using a genotypic, dominant, and recessive model. Mortality analysis in the Danish 1905 Birth Cohort was performed on all of the seven AKT1 SNPs using a left-truncated Cox proportional hazards model to adjust for late entry into the data set according to age.