Using sibpair analysis on centenarians and their siblings, Puca and colleagues (7) performed the first genomic screening for exceptional human longevity and reported linkage with a region on chromosome 4. Fine mapping of the candidateMedian age was 97 years for 64 men and offspring (n=145 total, 80 women, median age=69 years and 65 men, median age=68 years) and 288 Ashkenazi Jews (167 women, median age=74 years and 121 men, median age=75 years) who were not related to the earlier participants but from the same geographic area. The study population was identified from the Longevity Genes Study at Albert Einstein College of Medicine as described elsewhere (13,14), and the Einstein Aging Study, a community-based longitudinal study designed to identify predictive factors for cognitive decline and dementia (20,21). Participants were recruited through publicity and stated age was verified by checking birth certificates or U.S. passports in all participants. Medical history, demographic characteristics, and clinical data were obtained uniformly using a structured U-Shape Trend Analysis by means of a log-rank test. Wilcoxon statistics were calculated to test homogeneity between groups, and Cox proportional hazard models were used for survival analysis. The average time of follow-up for participants was 8.5 ± 0.3 and 8.7 ± 0.3 years for the buffered and unbuffered groups, respectively. Approximately 70% of the buffered groups and 64% of the unbuffered groups were still alive at the time of the analysis. In order to determine whether the MTPCC SNP is a buffered-deleterious genotype, we utilized the Buffering Mechanisms in Aging approach, whose statistical considerations are described in detail elsewhere (18). Briefly, controls and probands were grouped together, and a generalized linear model was used to fit the pattern of CC genotype prevalence with age. We confirmed the existence of a significant U-shape pattern with age using a binomial model incorporating both linear and quadratic terms for age and testing for the significant quadratic component using the equation: P(Y=1) = b + b age + b age^2, where Y = 1 was indicative of an individual having the MTPCC genotype. Maximum likelihood estimates of the coefficients b, b, and b were then obtained by the Fisher's scoring method, and the significance of the quadratic term (i.e., U-shape trend) was confirmed using the likelihood ratio test prior to performing interaction analysis on the MTPCC genotype.

Results:
Participant characteristics for aging cohorts from http://biomedgerontology.oxfordjournals.org/ at Ondokuz Mayis University on November 9, 2014 offspring and Ashkenazi controls are presented in Table 1. There were no significant differences observed between offspring and controls for glucose, insulin, apolipoproteins, LDL-C, or LDL particle size. Offspring did have greater levels of TG (p<.001) and tended to have elevated chylomicrons (p=.06), VLDL-TG (p=.06), and total cholesterol (p=.09), as compared with controls. However, offspring also had greater total unadjusted HDL-C (p<.01) and smaller HDL particle size (p<.001), though HDL-C was no longer significant after adjusting for several covariates.

Buffering Analysis:
Upon confirmation of a significant U-shape trend for the CC genotype in controls and probands, we then combined all offspring and control participants (excluding probands) harboring the CC genotype and subgrouped them by presence or absence of one or more longevity genotypes, including CETP (homozygosity for the 405 V allele, VV) [rs5882] (13), APOC3 (homozygosity for the 641 C allele, CC) [rs2542052] (14), and ADIPOQ(del/del APM1+2019) [rs56354395] (15). We next performed logistic regression to test the interaction between the trend of the MTPCC genotype across age with or without the presence of favorable longevity genotypes. Because we did not detect any additive effect of harboring more than one favorable genotype, any carrier of one or more of the three longevity genotypes were combined as a single group. To test the significance of interaction effects between age and genotype, the model testing for main effect only and the model testing for the interaction effects were compared using the log-likelihood ratio test.