The MTP gene product has been proposed to be involved in lipid metabolism and could plausibly play a pivotal role in the physiology of aging. However, given the observed discrepancies between US and French samples and uncertainty about the possible involvement of MTP in human longevity, further research is needed to determine whether MTP gene variation modifies human longevity.particular SNP (rs2866164) and a haplotype in the MTP gene were found to be associated with reduced longevity. In this study, the authors sought to replicate these findings in a German cohort of long-lived individuals (LLI) as well as French and U.S. controls. The authors found no evidence for an association between the tested SNPs and the longevity phenotype in any of the samples analyzed. Genotyping was performed using the Taqman Allelic Discrimination method, and genotype data were managed using an integrated database system. Statistical analysis included tests for deviation from Hardy-Weinberg equilibrium, chi-squared tests, and regression-based haplotype association tests. The authors also considered potential confounding factors such as age and gender. Finally, they discussed possible reasons for discrepancies between their results and those of Geesaman et al., who reported an association between MTP gene variants and longevity in U.S. Caucasians.SNP-haplotype in the MTP gene on chromosome 4q was implicated as a modifier of human lifespan (5). In the same publication, however, the authors reportedly failed to confirm their findings in a much larger sample from France, raising concerns about the validity of the original association. To critically evaluate these results, we have performed a large-scale study on 1,000 German nonagenarians and centenarians and 550 matched controls. The validity of our study population for longevity research has been supported by an examination of the apolipoprotein E (APOE) 2, 3, and 4 haplotypes, which revealed an increased frequency of 2 in LLI when compared with controls (0.118 vs. 0.085; odds ratio [CI] 1.45 [1.12-1.86]) (OR, odds ratio; CI, confidence interval) and a concurrently decreased frequency of 4 (0.071 vs. 0.145; OR [CI] 0.45 [0.36-0.57]). These results agree with other longevity studies and corroborate both the validity and efficacy of our study sample. Assuming an MTP risk factor frequency of 0.2 and a relative risk of 1.4 (characteristic values of the U.S. samples), our study sample would have had an 80% power to replicate the reported Table 3: Frequency of MTP risk haplotype rs2866164-G, MTP Q95 in German, French, and U.S. Caucasian LLI and controls Sample (no. of haplotypes) Frequency Germans LLI (2,036) 0.217 Centenarians (728) 0.224 Controls (1,066) 0.195 French LLI (1,126) 0.202 Controls (1,121) 0.197 U.S. Caucasians LLI, sample 1 (346) 0.176* Controls, sample 1 (364) 0.286 LLI, sample 2 (488) 0.193* Controls, sample 2 (462) 0.253 Second, inappropriate matching of cases and controls under even modest levels of population structure can lead to false positives and false-negative findings (15). Although the German control individuals were selected to ensure they were as close as possible to the LLI in terms of their age and geographic origin, systematic genetic differences between these samples cannot be completely excluded. Thus, latent population structure may have been responsible for the failure of the present study to confirm the association observed in the Americans, but this would not explain the negative finding in the French samples. Another reason for the lack of replication in both European samples could have been the higher proportion of males in the U.S. LLI. Men reach 100 years of age less often than women. It would therefore seem plausible that particular risk alleles impact more upon males than female mortality, so that these alleles are more strongly underrepresented in male than female centenarians. However, no gender-specific effect has been observed in the German samples. However, currently available evidence suggests that the putative association observed in the Americans (5) was due to recent changes in the genetic structure of the U.S. Caucasian population as a whole, rather than to genetic effects upon survival to old age. Although the known function of MTP in lipid metabolism renders it a plausible candidate for human longevity, the reported association appears likely to have been artifactual. The study by Geesaman et al. (5) thus highlights the potential pitfalls that arise when a case-control design is used as a means to map longevity genes in humans. Such studies would generally be hampered by the inherent difficulty of appropriately matching case and control samples simply because, if living individuals are compared, they were born generations apart. Our study also emphasizes the importance of replicating initial association findings in very large samples from different populations, especially for complex phenotypes in which genes with only weak or moderate effects are likely to play a role. Third, the observed discrepancy between the American control individuals and both European populations could reflect differences brought about by recent changes of the selective forces acting upon the MTP gene in the U.S. Caucasian population. During the first half of the 20th century, U.S. Caucasians became one of the most advanced societies in the world, with medical, technological, and sociological improvements that had not been experienced by earlier generations (represented by the U.S. LLI) or by contemporary Europeans. In large populations, even small changes of selective pressure can create considerable changes in allele frequencies over relatively short periods of time (16). Because it is not known whether MTP has functions (other than those in lipid metabolism, for instance, in reproductive or cognitive processes) that would render it a suitable target of natural selection, the type of selective pressure that might be involved remains