Admittedly, the history of genetic association with common multifactorial diseases is full of irreproducible studies with a reproducibility ratio of 16%, probably due to inflated estimates in small underpowered case-studies, inadequate selection of controls, and bias favoring positive associations. These failures in the past imply that studies on genetic variations and their association with multifactorial diseases must be very large if the results are to be trusted, and they must include the relevant population suited to answer the questions asked with as little bias as possible. To meet these demands, large prospective studies of the general population are the gold-standard: in his proposal for a prospective study in the US, Francis Collins states that (genetic) associations and estimation of their magnitude, consistency and temporality (all key criteria for epidemiological evidence of causal relationships) are best obtained through prospective, population-based cohort studies and that prospective cohort studies provide a valuable, feasible and indeed indispensable means of exploring the genetic basis of complex human diseases. In Denmark such a prospective study, The Copenhagen City Heart Study, was already established in theInterval, 0.9-1.1) vs. Arg/Arg homozygotes. Despite these beneficial effects of increased p53 activity for cancer resistance, mice overexpressing p53 age prematurely and even die earlier than their wild-type counterparts. Thus, activation of p53 is beneficial when the organism is young, but in older organisms it might reduce lifespan and even augment cancer risk, so-called antagonistic pleiotropy. In accordance with this concept, p53 accelerates aging when responding to cellular stress. In cell cultures, inactivation of normal p53 activity in senescent cells completely reverses the senescent arrest and allows the cells to resume cell divisions for many despite critically shortened telomeres. The germline truncating mutations of TP53, the gene coding for p53, are associated with a rare autosomal dominant disorder, the Li-Fraumeni syndrome. This syndrome is characterized by multiple primary neoplasms in children and young adults, with a predominance of soft-tissue sarcomas, osteosarcomas, breast cancer, brain tumors.

Participants (n = 9,219) of The Copenhagen City Heart Study were genotyped for the p53 Arg72Pro polymorphism using the Nanogen system. Taking advantage of the 100% complete follow-up, we were able to examine association between the Arg72Pro genotype and risk of any cancer (Fig. 3). For Arg/Pro heterozygotes vs. Arg/Arg homozygotes, we found a borderline increased gender and age-adjusted hazard ratio for all cancer of 1.1 (95% CI: 1.0-1.2), but since the equivalent hazard ratio for Pro/Pro homozygotes was nominally decreased at 0.9 (0.8-1.1), we considered this as a chance-finding.

Several germline SNPs in TP53 have been identified, most of them located in introns and of uncertain significance. The SNP rs1042522 is, however, located in exon 4 and results in an arginine to proline amino acid substitution in position 72 of the p53 protein. In 6 subtypes of cancer (gastrointestinal, respiratory, urologic, female, male and other types) including risk of melanoma and non-melanoma skin cancer (both in the other category), we generally did not find any association with Arg72Pro genotype (Fig. 3); surprisingly however, the risk of hematologic cancer increased 2-fold in Arg/Pro heterozygotes vs. Arg/Arg homozygotes (p < 0.001), with a similar trend in Pro/Pro homozygotes. This 2-fold increased risk was significant even after correction for multiple testing and therefore might represent a real phenomenon rather than a chance finding; however, this needs to be confirmed in another independent study.

We next sought to validate earlier findings suggesting association of Arg72Pro with risk of a variety of other diseases. However, in our study, Arg72Pro genotype was not associated with risk of cardiovascular or other diseases (Fig. 4, left).

Having examined Arg72Pro genotype and morbidity, we next examined mortality. The overall 12-year survival after blood sampling was increased in Arg/Pro heterozygotes with 3% (p = 0.003) and in Pro/Pro homozygotes with 6% (p = 0.002) vs. Arg/Arg homozygotes (Fig. 5, left). This corresponds to a sex and age-adjusted hazard ratio for death from any cause in Arg/Pro heterozygotes and Pro/Pro homozygotes vs. Arg/Arg homozygotes of 0.88 (95% CI: 0.81-0.96) and 0.82 (0.68-0.97), respectively (Fig. 4, right). This reduction in risk of death translates into an increased median survival of 2 years and 3 years for Arg/Pro heterozygotes and Pro/Pro homozygotes vs. Arg/Arg homozygotes (Fig. 5, right). In accordance with this, the frequency of Pro allele appeared to increase with increasing age, especially after age 90 years when the mortality of the participants begins to rise (Fig. 6). The Leiden 85-plus study found increased survival in Pro/Pro homozygotes vs. Arg/Arg homozygotes among 1226 participants aged 85 years or older followed for 5-10 years.

As already shown, the stepwise increased longevity in p53 Arg/Pro heterozygotes and Pro/Pro homozygotes vs. Arg/Arg homozygotes was not explained by decreased risk of developing cancer, cardiovascular diseasePhase 23. We therefore speculate that modulation of p53 is insignificantly, stepwise reduced with increasing number of Pro72 alleles (trend-test, p = 0.13) (Fig. 4, right). For all analyses described above, multifactorial adjustment for other potential confounders (cumulative tobacco consumption, smoking status, body mass index, alcohol consumption, plasma cholesterol, systolic blood pressure, and physical inactivity) gave similar risk estimates (data not shown).