The allele frequencies of the 629 C/A and D442G in Ashkenazi control groups were 0.57 and 0, respectively. Neither allele nor genotype frequencies of the 629 C/A variant differed significantly among probands, offspring, or Ashkenazi control groups, nor was this variant associated with lipoprotein levels or particle sizes. By contrast, allele frequencies of the I405V allele were 0.46, 0.43, and 0.29 in probands, offspring, and Ashkenazi control groups, respectively. Strikingly, the frequency of homozygosity for the codon 405 valine allele of CETP (VV genotype) was 24.8% in female and male probands compared with only 8.6% in Ashkenazi control groups. These differences were statistically significant in both men and women (P < .001 for both) (FIGURE 4).

Cholesteryl ester transfer protein has been shown to modulate HDL and LDL levels and sizes. To determine if genetic variation in CETP might influence lipoprotein particle size or longevity, we analyzed several common single nucleotide polymorphisms of CETP. All of the single nucleotide polymorphisms examined were in Hardy-Weinberg equilibrium in probands, their offspring, and the Ashkenazi control groups (Framingham Offspring Study samples were not genotyped). The offspring of probands had a VV genotype frequency of 20.7% in women and men combined, intermediate between probands and control groups and also significantly higher than in control groups (P = .004).

In principle, one cannot calculate the attributable risk of VV genotype for longevity from a case-control study because it is derived from incidence rates. However, a reasonable approximation can be calculated by using the estimation formula: where P is the prevalence of VV homozygosity in the population and OR is the odds ratio associating VV homozygosity with longevity. This estimation formula is valid so long as the outcome (longevity) is rare in the population (approximately 1 of 5000-10000). In our data, the OR (combining men and women) is 3.56. We do not have a direct observation of population prevalence of VV homozygosity in our data. However, it is reasonable to take the control groups as a proxy for the population as a whole because the number of people who will ultimately survive to longevity is a very small proportion of the population. Our estimate of the prevalence of VV homozygosity is 0.09, and applying the formula, population attributable risk fraction is 18.1.

We also assessed the relationship between CETP I405V genotype and lipoprotein particle sizes and CETP activity in the control, offspring, and proband groups, respectively. The VV phenotype was associated with significantly larger LDL and HDL particle sizes (TABLE 3). Furthermore, participants with the VV genotype had 17% lower CETP concentrations compared with those with II or IV genotype, and HDL level and CETP levels were negatively correlated.(r=0.29; P=.03; Spearman p). These findings suggest a survival advantage for individuals with the VV genotype, perhaps mediated through decreased levels of CETP and its effects on lipoproteins and their particle sizes. The frequency of homozygosity for the codon 405 isoleucine to valine (I405V) allele of cholesteryl ester transfer protein (CETP) in female and male probands (n=156), offspring (n=163), and Ashkenazi controls (n=129). The frequency of the VV genotype is 2.4- and 2.9-fold increased in offspring and probands, respectively, compared with Ashkenazi controls. *P=.001; P=.20; P=.004; P<.001, indicating differences between probands and offspring vs Ashkenazi controls for women and men.

Table 3. CETP I405V Genotype and Lipoprotein Characteristic and Plasma CETP Levels in Families With Exceptional Longevity and Control Groups

CETP I405V Genotype, Mean (SD) P Value (VV vs Variable Genotypes) HDL Concentration, mg/dL 57 (18) 55 (16) 55 (16) .53 Large particle size, % of total 56 (16) 60 (14) 60 (15) .10 Particle size, nm 9.28 (0.56) 9.09 (0.52) 9.07 (0.48) .02 LDL Concentration, mg/dL 114 (35) 120 (30) 123 (34) .16 Large particle size, % of total 67 (25) 58 (24) 56 (28) .02 Particle size, nm 21.29 (0.67) 20.98 (0.63) 20.88 (0.81) .002 CETP concentration, g/mL 1.65 (0.59) 1.92 (0.65) 1.99 (0.72) <.001

COMMENT

Abbreviations: CETP, cholesteryl ester transfer protein; HDL, high-density lipoprotein; I405V, codon 405 valine; LDL, low-density lipoprotein. SI conversion factor: To convert HDL and LDL concentrations to mmol/L, multiply by 0.0259.

(Reprinted) JAMA, October 15, 2003 Vol 290, No. 15 2037 2003 American Medical Association. All rights reserved.

Because it has been shown that lipoprotein sizes are genetically determined,33 we were interested in finding potential pathways involved in this phenotype. The biology of rare forms of CETP deficiency may be relevant to our observation of a marked increase in the frequency of homozygosity for the common codon 405 valine CETP allele in our families with longevity. Although homozygosity for this variant was observed in 24.8% of our probands, it was present at a frequency of only 8.6% in Ashkenazi Jewish control participants. Offspring of long-lived individuals also had a much higher frequency of the VV genotype compared with control groups.

With analyses of 30 different single nucleotide polymorphisms, it could be argued that our positive finding for I405V CETP is the result of multiple comparisons. However, the level of statistical significance of this association (P<.001) maintains statistical significance even after rigorous correction for multiple comparisons. Furthermore, investigation of this variant was hypothesis-driven based on known pathways of lipoprotein metabolism.