Postprandial responses of plasma lipids and lipoproteins in subjects with apoA-I(Lys107-->0)

Quantile-dependent expressivity of postprandial lipemia

Purpose

“Quantile-dependent expressivity” describes an effect of the genotype that depends upon the level of the phenotype (e.g., whether a subject’s triglycerides are high or low relative to its population distribution). Prior analyses suggest that the effect of a genetic risk score (GRS) on fasting plasma triglyceride levels increases with the percentile of the triglyceride distribution. Postprandial lipemia is well suited for testing quantile-dependent expressivity because it exposes each individual’s genotype to substantial increases in their plasma triglyceride concentrations. Ninety-seven published papers were identified that plotted mean triglyceride response vs. time and genotype, which were converted into quantitative data. Separately, for each published graph, standard least-squares regression analysis was used to compare the genotype differences at time t (dependent variable) to average triglyceride concentrations at time t (independent variable) to assess whether the genetic effect size increased in association with higher triglyceride concentrations and whether the phenomenon could explain purported genetic interactions with sex, diet, disease, BMI, and drugs.

Results

Consistent with the phenomenon, genetic effect sizes increased (P≤0.05) with increasing triglyceride concentrations for polymorphisms associated with ABCA1, ANGPTL4, APOA1, APOA2, APOA4, APOA5, APOB, APOC3, APOE, CETP, FABP2, FATP6, GALNT2, GCKR, HL, IL1b, LEPR, LOX-1, LPL, MC4R, MTTP, NPY, SORT1, SULF2, TNFA, TCF7L2, and TM6SF2. The effect size for these polymorphisms showed a progressively increasing dose-response, with intermediate effect sizes at intermediate triglyceride concentrations. Quantile-dependent expressivity provided an alternative interpretation to their interactions with sex, drugs, disease, diet, and age, which have been traditionally ascribed to gene-environment interactions and genetic predictors of drug efficacy (i.e., personalized medicine).

Conclusion

Quantile-dependent expressivity applies to the majority of genetic variants affecting postprandial triglycerides, which may arise because the impaired functionalities of these variants increase at higher triglyceride concentrations. Purported gene-drug interactions may be the manifestations of quantile-dependent expressivity, rather than genetic predictors of drug efficacy.

Effect of desirable fasting triglycerides on the postprandial response to dietary fat

BACKGROUND

The National Cholesterol Education Program (NCEP) recently revised the "desirable" fasting triglyceride (TG) to < 150 mg/dL, and levels exceeding 200 mg/dL are defined as "high."

METHODS

To evaluate the postprandial response to dietary fat, 50 studies were conducted in nonobese, normocholesterolemic subjects. Following an overnight fast, subjects consumed an oral fat load (70 g/m2), and postprandial triglyceride (ppTG) measurements were assessed at 2, 4, 6, and 8 hours. Subjects were divided by fasting TG cutpoints of 100 and 150 mg/dL.

RESULTS

The prevalence of ppTG samples exceeding 200 mg/dL was significantly lower with fasting TG < 100 mg/dL (n = 116) compared with TG 100 to 150 mg/dL (n = 56) (8% versus 25%; p = .004, chi-square analysis). In addition, fasting TG < 100 mg/dL (n = 29) was associated with a reduced mean 4-hour peak ppTG level compared with fasting TG > 100 mg/dL (n = 21) (125 mg/dL versus 249.8 mg/dL; p < .0001). Multiple linear regression analysis identified fasting TG as the most important determinant of the postprandial response after adjustment for other covariates (p = .0005).

CONCLUSIONS

Because ppTG-rich lipoproteins contribute to coronary heart disease risk, fasting TG < 100 mg/dL may be a more desirable cutpoint than fasting TG < 150 mg/dL in coronary heart disease risk factor assessment.