Am. J. Hum. Genet. 49:1145-1154, 1991
Role of Apolipoprotein E and B Gene Variation in Determining Response of Lipid, Lipoprotein, and Apolipoprotein Levels to Increased Dietary Cholesterol Eric Boerwinkle,* Spencer A. Brown,T Kathryn Rohrbach,t Antonio M. Gotto, Jr.,t and Wolfgang Patscht *Center for Demographic and Population Genetics, University of Texas Health Science Center, and tDepartment of Medicine, Baylor College of Medicine and The Methodist Hospital, Houston
Summary A large segment of the population is modifying its dietary cholesterol intake to achieve a healthier life-style. However, all individuals do not respond equally. We have investigated the effects that that two physiologically important polymorphisms in the apolipoprotein (apo) E and B genes have on the responses of plasma lipid, lipoprotein, and apolipoprotein levels to a high-cholesterol diet. Over a 6-wk period, individuals were prescribed two diets, one consisting of 300 mg dietary cholesterol/d for 3 wk and one consisting of 1,700 mg dietary cholesterol/d for 3 wk. Total cholesterol, low-density-lipoprotein cholesterol (LDL-C), and apo B levels were significantly increased on the high-cholesterol diet. Average total cholesterol (numbers in parentheses are SDs) went from 167.6 (23.4) mg/dl on the low-cholesterol diet to 190.8 (36.2) mg/dl on the high-cholesterol diet; LDL-C went from 99.9 (24.8) mg/dl to 119.2 (33.4) mg/dl, and apo B went from 74.9 (24.5) mg/dl to 86.8 (29.5) mg/dl. In 71 individuals, the frequencies of the apo s2, £3, and s4 alleles were .09, .84, and .07, respectively. The frequency of the longer, apo B signal peptide allele (5'O1SP27) was .68. Apo g2/3 individuals had significantly lower LDL-C levels than did £3/3 homozygotes, on both the lowcholesterol diet (LDL-C lower by 21 mg/dl) and the high-cholesterol diet (LDL-C lower by 27 mg/dl). Average triglyceride levels were significantly different among apo B signal peptide genotypes, with the 5'DSP27/37 homozygotes having the lowest levels (70 mg/dl). When individuals were switched from the low-cholesterol diet to the high-cholesterol diet, in no case were the average responses in lipid levels significantly different among apo E or B genotypes. Therefore, these gene loci do not have a major effect on the response of lipid levels to increased dietary cholesterol. Introduction
Epidemiological, clinical, and animal research studies have linked plasma cholesterol with the occurrence of atherosclerosis and increased risk of coronary heart disease (CHD) (Kannel et al. 1971; Clarkson et al. 1979; Ross 1988). Although the data are not unequivocal, one method advised for reducing total serum cholesterol levels is diet. The National Cholesterol EdReceived February 4, 1991; final revision receivedJuly 26, 1991. Address for correspondence and reprints: Eric Boerwinkle, Ph.D., Center for Demographic and Population Genetics, University of Texas Health Science Center, P.O. Box 20334, Houston, TX 77225. i 1991 by The American Society of Human Genetics. All rights reserved. 0002-9297/91 /4906-0002$02.00
ucation Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (NCEP ) has advised general and specific dietary guidelines for reducing total serum cholesterol levels and CHD risk. However, all individuals do not respond equally to dietary modification; the cholesterol levels of some individuals decrease considerably, while those ofothers remain relatively unchanged. Katan et al. (1986) demonstrated the existence of consistent hypo- and hyperresponders to dietary cholesterol, and numerous animal-model studies suggest that genetic factors contribute to interindividual variation of plasma cholesterol in response to dietary change (Clarkson and McMahan 1980). There are conflicting reports on the effects that the 1145
apolipoprotein (apo) E polymorphism has on the response to dietary modification in a high-risk community (Tikkanen et al. 1990; Xu et al. 1990a). Apo E is a structural component of circulating chylomicrons, very-low-density lipoproteins, and high-density lipoproteins and is a ligand for several classes of lipoprotein receptors. Human apo E is polymorphic, with three common alleles: 82, 83, and 84 (Utermann et al. 1977). Numerous studies have shown that the average effect of the £2 allele is to lower total serum cholesterol and that the average effect of the 84 allele is to raise total cholesterol levels (reviewed in Davignon et al. 1988). Boerwinkle and Utermann (1988) have hypothesized that these effects may be modulated by dietary modification. In the present paper we investigate the effect that the apo E polymorphism has on the response to a high-cholesterol diet in a sample of normocholesterolemic individuals. We also investigate the role of variation in the signal peptide of apo B, another polymorphism of potential physiological significance for the response of lipid levels to dietary modification. The signal peptide of apo B is polymorphic, with alleles differing in length (Boerwinkle and Chan 1989). The common allele (5'13SP27) has 27 amino acids and two copies of a leucine-alanine-leucine repeat, whereas the less common allele (5'jBSP24) has only one copy and 24 amino acids. Xu et al. (1990b) have reported that average triglyceride levels are different among signal peptide genotypes when individuals are consuming their normal diets. These effects were not statistically significant when the same individuals consumed a diet low in fat (Xu et al. 1990b). The exact mechanism of these signal peptide effects is unknown, but the signal peptide is critical for the translocation of the nascent polypeptide into the lumen of the endoplasmic reticulum (Randall and Hardy 1989). The results presented here suggest that, although both the apo E and B polymorphism affect lipid levels, they do not significantly influence the response to the high-cholesterol diet. Subjects and Methods Subjects and Study Protocol Subjects were recruited from the Texas Medical Center area (including the University of Texas Health Science Center, Baylor College of Medicine, and The M. D. Anderson Hospital and Tumor Institute). Inclusion criteria were as follows: healthy males 20-50 years of age; within 30% of ideal body weight as deter-
Boerwinkle et al.
mined by Metropolitan Life Insurance Tables; and, by initial screening procedures,