XbaI polymorphism of the apolipoprotein B gene and plasma lipid and lipoprotein response to dietary fat and cholesterol: a clinical trial

Abstract

A dietary trial was carried out on a group of offspring whose parents were hospitalized for an acute myocardial infarction. The XbaI Restriction Fragment Length Polymorphism (RFLP) was used to examine the genetic contribution of variation at this apo B locus to the response of lipids and lipoproteins to dietary manipulations. Twenty participants were homozygotes for the 8.0 kb fragment (X1X1), two were homozygotes for the 5.0 kb fragment (X2X2), and 15 were heterozygotes (X1X2). Subjects were randomized to a 5-week crossover study. Half began on a low SFA--cholesterol (LSC) diet for 5 weeks and, after a washout period of 4 weeks, they were placed on a high SFA--cholesterol (HSC) diet for a second period of 5 weeks. This order was reversed in the second group of participants. Significant changes in total cholesterol, LDL-C, and apo B were observed when subjects were moved from the LSC to the HSF diet. The corresponding average change induced by the dietary manipulations in X1X1 subjects compared with subjects with X2 allele were: 18.1 +/- 17.6 mg/dl and 9.5 +/- 19.6 mg/dl for total cholesterol and 15.8 +/- 15.3 mg/dl and 4.8 +/- 20.9 mg/dl for LDL-C, respectively. Our observation indicated that variation at the apo B XbaI locus may interact with baseline levels to determine individual dietary response in LDL-C level. However, the differences between the genotypic classes were not statistically significant, suggesting that the apo B XbaI locus is not a major determinant of interindividual differences in lipid and lipoprotein response to diet in this population.