role in the metabolism of cholesterol and TG by binding to receptors on the liver to help mediate clearance of chylomicrons and very low- density-lipoprotein(VLDL)fromthebloodstream.Inaddition,polymor- phisms in the CETP and APOE genes have been reported to possibly confer risk against longevity and lipid homeostasis. CETP I405V poly- morphism is a common SNP (rs5882) in exon 14 of the CETP gene, which was previously identified as a longevity gene (Barzilai et al., 2003). The VV genotype of I405V was reported to be associated with lower CETP concentrations and higher HDL-c concentrations. Isoforms of APOE are produced from haplotype combinations of rs429358 and rs7412 polymorphisms (defining the APOE*ε2, ε3, and ε4 haplotypes). APOE haplotypes have been extensively studied and indicated APOE*4 to be a risk factor for LDL-c, Alzheimer's disease and longevity in some ethnicities. Previous studies by the Global Lipids Genetics Consortium indicated that the lipid components might share certain risk susceptible polymorphisms. Our recent pilot study in oldest-old Chinese subjects indicated a different serum lipid pattern in which TG was decreased without an increase of HDL-c as reported in Ashkenazi Jews (Barzilai etal.,2003).Fewstudieshavebeenreportedaboutthegeneticcontribu- tion of CETP and APOE to hTG, especially in oldest-old subjects.

2.3. Statistical analysis

Statistical Package for Social Sciences (SPSS; SAS Institute, Cary, NC, USA)Windows,version12.0andSTATA10.0software(StataCorp,College Station, TX, USA) was used. Allele frequencies were determined by gene counting and the goodness-of-fit for Hardy–Weinberg equilibrium (HWE) was verified using Chi-square analysis. One-way ANOVA or Student t-test were used when comparing continuous variables between groups;Chi-squareanalysisforcategoricalvariable.Backwardconditional logistic regression was conducted in multivariate analysis to estimate the gene–gene interaction item and adjust for the confounding of age, APOE*4 status, alcohol drinking, body mass index (BMI), TC, HDL-c, LDL-c. The odds ratio (OR) and 95% confidence intervals (95%CI) were used to estimate the association between variables. An additive model was used to code SNPs for the ‘risk’ allele, the allele that increased the probability of being a case. Accordingly, ‘0’ indicated that the subject was homozygous for the non-risk allele; the heterozygote was coded ‘1’, and those who were homozygous for the risk allele were coded ‘2’. Multifactor Dimensionality Reduction (MDR, version 1.2.2) was also used to confirm the gene–gene interaction (epistasis) from the logistic regression analysis (Hahn et al., 2003). We used 10,000 permutations to determine the statistical significance of the best models. These data were also analyzed by using an extension of the MDR algorithm that includes adjustment for covariates, the Generalized Multifactor Dimen- sionality Reduction (GMDR, V0.7) software package. Two-sided P b 0.05 was considered statistically significant. Power were estimated with the program Genetic Power Calculator (http://pngu.mgh.harvard.edu/ ~purcell/gpc/cc2.html) (Purcell et al., 2003).

Gene–gene epistatic interactions are essential to identify genetic markers for polygenic traits that are unable to be captured by single marker analysis and/or revealed by the combinatory effect of loci in other pathways (Ndiaye et al., 2013). Thus, we hypothesized that the polymorphisms of CETP and APOE might interact in the signaling path- way, which could have greater effects on the dysregulation of serum lipids in oldest-old Chinese women. This study was conducted to assess potential CETP*APOE interaction and contribution to dyslipidemia in oldest-old Chinese women by the traditional parametric approach of logisticregressionandthenonparametricmethodofmultifactordimen-

2. Materials and methods

2.1. Subjects

The current study was based on the Longevity and Health of Aging Population in GuangxiChinastudyconducted in 2008 and 2010.Yongfu County has been qualified as the longevity town by Geriatric Society of China in 2007.

3. Results

We analyzed a total of 713 female Chinese subjects, including 372 oldest-old subjects and 340 controls in the present study. Subjects in oldest-old grouphad significantly lower TGand BMI;and higher FPG, LDL-c, HR, SBP and DBP when compared with controls (Table 1).

Sevenhundred andthirteenfemale volunteers,fromurbanand rural areas of Yongfu County, South China, were enrolled after having been excluded from the subjects undertaking lipid-lowering drugs. The longevity group comprised of 16 centenarians (aged 100–109), 322 no- nagenarians(aged90–99)and34octogenarians(aged80–89).Thegeog- raphy and nationality matched control group consisted of 340 unrelated volunteers(aged20–58,meanage41.88± 12.20 years)withoutlongev- ity history (no lineal family members aged above 80 for 3 generations). All subjects self-reported as belonging to Han nationality. The Ethics Committee of Beijing Hospital, Ministry of Health approved the study protocol. All participants were informed and provided with informed consent in writing.

Distributions of CETP and APOE polymorphisms in the oldest-old group and controls were in HWE (Table 2). Comparison between oldest-old and controls showed that, as expected, APOE*4 was less

Table 1

Demographic details of the female sample set.

Oldest-old subjects Controls P t-test Number (n) 372 340 Age (years) 92.83 ± 3.74 41.88 ± 12.20 FPG (mmol/L) 5.69 ± 1.44 5.41 ± 1.57 0.019 TC (mmol/L) 4.83 ± 1.09 4.74 ± 0.99 0.258 TG (mmol/L) 1.45 ± 0.81 1.70 ± 1.15 0.001 HDL-c (mmol/L) 1.25 ± 0.36 1.21 ± 0.28 0.070 LDL-c (mmol/L) 2.97 ± 0.98 2.76 ± 0.98 0.005 BMI (kg/m2) 18.30 ± 3.45 22.70 ± 3.97 0.001 HR (times/min) 80.35 ± 12.20 71.81 ± 9.15 0.001 SBP (mmHg) 154.72 ± 25.91 117.15 ± 20.27 0.001 DBP (mmHg) 82.01 ± 14.30 73.26 ± 13.12 0.001

2.2. Methods