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 proline > 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 (Hamanishi 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 regression 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., 1999spelling errors or incorrectly combined words in the text. However, there are some grammatical errors that need to be corrected.

1. In the sentence "The combined CT/TT group showed a statistical significant coefficient," "statistical significant" should be changed to "statistically significant."

2. In the sentence "Still, a moderate increased ADL score may indicate that the individuals holding the genotypes associated with decreased mortality tended to be less disabled, which corresponds well with a tendency of a better self reported," "increased" should be changed to "increase."

3. In the sentence "Never- theless, a moderate increased MMSE for the rs4880 MnSOD SNP genotype individuals indicates a moderate increased cognitive function of the individuals holding the genotypes associated with decreased mortality," "increased" should be changed to "increase."

4. In the sentence "The rs1050450 GPX1 SNP genotype frequencies in the 1905 cohort deviate from the once expected from the observed allele frequencies," "once" should be changed to "ones."

5. In the sentence "This might indicate an antagonistic pleiotropic effect of the SNP in Danes; TT individuals might have an increased mortality from middle age to very old age (as compared to CC and CT individuals), whereas in very old age TT individuals have a survival advantage," "very old age" should be changed to "old age."

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0.296, 95%CI = [0.0189 0.0622], N = 1633). With respect to the rs1050450 GPX SNP, a positive statistically significant sex-adjusted coefficient of 0.0783 (P = 0.039, 95%CI = [0.0039 0.1528], N (CT) = 726) was found for the CT genotype, while a positive but non-significant coefficient of 0.0359 (P = 0.605, 95%CI = [0.1001 0.1719], N (TT) = 129) was found for the TT genotype. The combined CT/TT group showed a statistically significant coefficient of 0.0216 (P = 0.049, 96%CI = [0.0002 0.0717], N = 1596). Still, a moderate increase in ADL score may indicate that the individuals holding the genotypes associated with decreased mortality tended to be less disabled, which corresponds well with a tendency of better self-reported health. Finally, the MMSE criteria showed a positive coefficient for the rs4880 MnSOD SNP CC/CT group; sex-adjusted coefficient CC/CT = 0.404 (P = 0.015, 95%CI = [0.0790 0.7296], N = 1582). With respect to the rs1050450 GPX1 SNP, a coefficient of 0.307 (P = 0.309, 95%CI = [0.2855 0.9001], N (CT) = 708) for the CT genotype and a coefficient of 0.267 (P = 0.627, 95%CI = [1.3484 0.8131], N (TT) = 126) for the TT genotype were found. Nevertheless, a moderate increase in MMSE for the rs4880 MnSOD SNP genotype individuals indicates a moderate increase in cognitive function of the individuals holding the genotypes associated with decreased mortality.

Fig. 2 shows Kaplan-Meier survival estimates for the 1905 cohort by sex and rs4880 MnSOD SNP genotype. (A) Females and (B) males. N (females) = 1185, N (males) = 465.

4. Discussion

3.3. Gender-related differences in survival