AKT1 fails to replicate as a longevity-associated gene in Danish and German nonagenarians and

Marianne Nygaard*,1,2, Mette Soerensen1,2, Friederike Flachsbart3, Jonas Mengel-From1,2, Qihua Stefan Schreiber3, Almut Nebel3, Kaare Christensen1,2,4 and Lene Christiansen1,2

In addition to APOE and FOXO3, AKT1 has recently been suggested as a third consistent longevity gene, with variants in AKT1 found to be associated with human lifespan in two previous studies. Here, we evaluated AKT1 as a longevity-associated gene across populations by attempting to replicate the previously identified variant rs3803304 as well as by analyzing six additional AKT1 single-nucleotide polymorphisms, thus capturing more of the common variation in the gene. The study population was 2996 long-lived individuals (nonagenarians and centenarians) 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 supportive nominal indication of a disadvantageous effect of rs3803304 was found in a restricted group of Danish centenarian men. Overall, our results do not support AKT1 as a universal longevity-associated gene. European Journal of Human Genetics (2013) 21, 574–577; doi:10.1038/ejhg.2012.196; published online 29 August 2012

Keywords: human longevity; AKT1; association

INTRODUCTION

In this study, we evaluated AKT1 as a longevity-associated gene across populations by analyzing rs3803304 in a large sample of Danish and German long-lived individuals with the aim of replicating the previous finding. Further, we included six additional AKT1 SNPs in order to cover more of the common variation within the gene.

Despite the fact that approximately 25% of variation in human lifespan is attributable to genetic factors,1 polymorphisms in only a few candidate genes have so far been consistently found to be associated with longevity.

The first to be discovered, and also the most prominent candidate, is the apolipoprotein E (APOE) gene. The APOE e4 haplotype has repeatedly been reported as an age-related mortality factor in numerous populations,2 and recently, the APOE e4 allele was confirmed to negatively affect survival into old age in two genome- wide association studies (GWASs).3,4

MATERIALS AND METHODS

Study populations

Danish study. The Danish study population comprised 1383 participants from The Danish 1905 Birth Cohort Study, described in details elsewhere.12 Briefly, the study was initiated in 1998, when participants were 92–93 years of age and follow-up studies of surviving participants were carried out in 2000, 2003 and 2005, when participants reached 100 years of age.

The forkhead box O3 (FOXO3) gene, which encodes a transcription factor involved in the insulin/insulin-like growth factor 1 (IGF1) pathway, has been presented as another well-established candidate. The insulin/IGF1 pathway has repeatedly been implicated in longevity in various model organisms,5 as well as in humans, where the FOXO3 association has been demonstrated in a number of populations of diverse ethnic origin.6–11

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.13 A total of 143 of the 1089 individuals (women proportion of 79%) lived to be at least 100 years of age.

The newest candidate that has been put forward as a third consistent longevity gene is AKT1, which is also part of the insulin/ IGF1 pathway. Single-nucleotide polymorphisms (SNPs) in this gene have been associated with longevity in two studies: in 2009, Pawlikowska et al9 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.3

Vital status was followed until death or until 1 January 2011, resulting in a mean follow-up time for survivors of 12.4 years (range: 12.2–12.6). Informa- tion on survival status was retrieved from the Danish Central Population Register, which is continuously updated.14

A group of 736 younger control individuals (mean age 50.6 years) were randomly selected from the population-based study of middle-aged Danish twins,15 which was initiated in 1998 with the random selection of 2640 intact twin pairs born from 1931 to 1952. Here, only one twin from each pair was included.

1Epidemiology, Institute of Public Health, University of Southern Denmark, Odense C, Denmark; 2Department of Clinical Genetics, Odense University Hospital, Odense C, Denmark; 3Institute of Clinical Molecular Biology, Christian-Albrechts University, Kiel, Germany; 4Department of Clinical Biochemistry and Pharmacology, Odense University Hospital, Odense C, Denmark *Correspondence: M Nygaard, Epidemiology, Institute of Public Health, University of Southern Denmark, J.B. Winsloews Vej 9B, Odense C 5000, Denmark. Tel: +45 65412822; Fax: +45 65414875; E-mail: mnygaard@health.sdu.dk Received 9 May 2012; revised 10 July 2012; accepted 3 August 2012; published online 29 August 2012

1 Characteristics of the study populations

German study. The German study population included 865 nonagenarians and 748 centenarians (age range 95–110 years, mean age 98.9 years, women proportion of 73.0% in all cases and 80.5% in centenarians). The control individuals were 1104 younger unrelated individuals (age range 60–75 years, mean age 67.2 years). The participants were recruited from different geographic regions of Germany and were all of German ancestry.16