The human gene encoding GPX1 is designated GPX1 (http:// www.genenames.org/data/hgnc_data.php?hgnc_id=4553). GPX1 contains a c.599C>T SNP (previously referred to as c.593C>T), which is also referred to as rs1050450 (http://www.ncbi.nlm.- nih.gov/SNP/snp_ref.cgi?rs=1050450)). The SNP leads to a proli- ne > leucine substitution, hence the SNP is also referred to as p.P200L (however, previously it was referred to as Pro198Leu (see e.g. (Moscow et al., 1994)). The SNP likely affects the activity of the variant proteins (Ravn-Haren et al., 2006). In this paper we will refer to the SNP as the rs1050450 GPX1 SNP. The T allele of the rs1050450 GPX1 SNP has been associated with bladder, lung and breast cancers (Ratnasinghe et al., 2000; Hu and Diamond, 2003; Ichimura et al., 2004), diabetic associated atherosclerosis (Hama- nishi et al., 2004), intracerebral hemorrhage (Pera et al., 2008), metabolic syndrome (Kuzuya et al., 2008), and coronary artery disease (Tang et al., 2008).

2.3. Statistics

The STATA 10.0 statistical program (Stata Corporation, College Station, TX, USA) was used for statistical analysis. The x2 test was used for comparing genotype frequencies and for Hardy–Weinberg equilibrium testing. For comparing the functional and cognitive abilities between groups linear regressing was applied. Mortality risks/hazard ratios (HR) were estimated using the Cox proportional hazard model. Statistical significance was set as P < 0.05.

3. Results

3.1. Genotype frequencies

The genotype frequencies of the rs4880 MnSOD SNP and of the rs1050450 GPX1 SNP in the Danish 1905 cohort are summarized in Table 1. The allele frequencies for the rs4880 MnSOD SNP were 49.9% for C and 50.1% for T, while for the rs1050450 GPX1 SNP they were 69.1% for C and 30.9% for T, which correspond with previous reports in Caucasians (Ambrosone et al., 1999; Van Landeghem et al., 1999; Ravn-Haren et al., 2006). The p-values for Hardy– Weinberg disequilibrium were 0.88 for the rs4880 MnSOD SNP and 0.005 for the rs1050450 GPX1 SNP. Compared to a previous study of the rs1050450 GPX1 SNP genotype frequencies in 798 middle

To our knowledge, no studies have been published regarding an association of the rs1050450 GPX1 SNP with human survival. Three cross sectional studies have investigated the association of the rs4880 MnSOD SNP with human survival yet with inconsistent results (De Benedictis et al., 1998; Stessman et al., 2005; Taufer et al., 2005).

In the present study, we evaluated the association of the MnSOD and the rs1050450 GPX1 SNPs with longevity in a

Table 1

The rs4880 MnSOD SNP and rs1050450 GPX1 SNP genotype frequencies in the Danish 1905 cohort. 1905 cohort: the Danish 1905 cohort.

The rs4880 MnSOD SNP in the 1905 cohort (N = 1650) Thers4050450GPXISNPinthe1905cohort(N = Female Male Total Female Male Total Participants 1185 465 1650 Participants 1160 453 1613 Female:males 71.8% 28.2% 100% Female:males 71.9% 28.1% 100% Number of deaths 1140 (96.2%) 449 (96.6%) 1589 (96.3%) Number of deaths 1115 (96.1%) 437 (96.5%) 1552 (96.2%) Genotype Genotype CC 284 (24%) 128 (27.5%) 412 (25%) CC 539 (46.5%) 207 (45.7%) 746 (46.2%) CT 589 (49.7%) 233 (50.1%) 822 (49.8%) CT 536 (46.2%) 201 (44.4%) 737 (45.7%) TT 312 (26.3%) 104 (22.4%) 416 (25.2%) TT 85 (73%) 45 (9.9%) 130 (8.1%) Allele frequency C:T 48.8%:51.2% 52.6%:47.4% 49.9%:50.1% Allele frequency C:T 69.6%:30.4% 67.9%:32.1%

Table 2

size and indicate a survival advantage of CT and TT individuals in old age, although not significant for the TT genotype. Combining the CC and TT individuals shows a HR of 0.93 (P = 0.008). The survival data is summarized in Table 2.

Mortality risk according to the rs4880 MnSOD SNP genotypes or to the rs1050450 GPX1 SNP genotypes. 1905 cohort: the Danish 1905 cohort. HR: hazard ratio. CI: confidence interval.

The rs4880 MnSOD SNP genotypes HR 95%CI p-value TT 1 – – CT 0.82 0.756–0.998 0.048 CC 0.87 0.727–0.925 0.001 CC/CT 0.91 0.864–0.967 0.002 The rs1050450 GPXI SNP genotypes HR 95%CI p-value CC 1 – – CT 0.87 0.787–0.968 0.010 TT 0.88 0.729–1.068 0.202 TT/CT 0.93 0.889–0.982 0.008

When fitting these sex adjusted mortality risk estimates to their respective Kaplan-Meier Survival estimates, there was good correspondence (data not shown), validating the use of the Cox proportional hazard model. The Kaplan-Meier Survival estimates when combining carriers of the minor allele are shown in Fig. 1.

These survival data indicate that both the rs4880 MnSOD SNP and the rs1050450 GPX1 SNP may be mortality risk factors.

Proportion survivingProportion surviving1.000.750.500.250.001.000.750.500.250.00(A) Kaplan-Meier survival estimates byrs4880 MnSOD SNP genotypes— TT— CTICC  T T T T0 1000 2000 3000 4000Analysis time (days)(B) Kaplan-Meier survival estimates byrs1050450 GPX1 SNP genotypesccCTITT 4000 2000 3000 4000Analysis time (days)

aged Danes (Raaschou-Nielsen et al., 2007), the frequencies of CC and CT individuals in our 1905 cohort were not significantly different (p-value, P = 0.66), yet we did observe a slightly lower frequency of TT individuals. Genotype frequencies were not different between males and females (P (rs4880) = 0.15, P (rs1050450) = 0.23), therefore the combined frequencies were used for the subsequent survival analyses and association studies of the age-related phenotypes.

3.2. Longevity