Genetic studies of human apolipoproteins. XVII: Population genetics of apolipoprotein polymorphisms in American Samoa

Population genetics of apolipoproteins A-IV, E, and H, and the angiotensin converting enzyme (ACE): associations with lipids, and apolipoprotein levels in American Samoans

Distributions of alleles at three apolipoprotein loci (APO E, APO H, and APO A-IV) and an insertion/deletion (I/D) polymorphism at the angiotensin converting enzyme (ACE) locus among 274 American Samoans are described here. Genotypes at each locus are examined for associations with quantitative lipid (total cholesterol (total-c), LDL-cholesterol (LDL-c), HDL-cholesterol (HDL-c), and triglycerides) and apolipoprotein (APO AI, APO AII, APO E, and APO B) levels. Genotype frequencies at all four loci are in Hardy-Weinberg equilibrium. The most common APO A-IV genotype (1-1) was observed in 252 American Samoans (97%). The three most common APO E genotypes were 3-3 (47%), 3-4 (30%), and 2-3 (12%). The most frequent APO H genotype was 2-2 (86%). The most common ACE genotype (I/I) was observed in 75% of sampled individuals, and 23% were I/D heterozygotes. APO E genotypic variation was associated with total-c, HDL-c, LDL-c, and all four quantitative apolipoproteins (AI, AII, E, and B). APO A-IV genotypes were associated significantly with total cholesterol, LDL-c, and APO-B levels. APO H showed little association with any quantitative lipid or apolipoprotein. ACE D/D homozygotes had higher AII levels. ACE showed a consistent association with APO AII levels, with either APO A-IV or APO E as a covariate. The interaction term between ACE and APO E was also significantly associated with total-c and APO E levels, and the ACE genotype showed a significant main effect on APO AI levels in multivariate analyses.

Apolipoprotein A-IV-2 allele: association of its worldwide distribution with adult persistence of lactase and speculation on its function and origin

Apolipoprotein A-IV (apo A-IV) is a 46-Kd plasma glycoprotein that may play a major role in intestinal lipid absorption. A genetic polymorphism in the apo A-IV gene, apo A-IV-2, encodes a His-->Gln substitution at codon 360 that alters the biological function of this apolipoprotein. As the worldwide distribution of the apo A-IV-2 allele appeared similar to the frequency of a genetic polymorphism that determines the persistence of lactase into adulthood, we examined the relationship between the apo A-IV-2 and lactase persistence polymorphisms by compiling the prevalence of adult lactase persistence in all populations in which the frequency of the apo A-IV-2 allele has been determined. Across 29 groups, there was an extremely strong correlation (4 = 0.937, P < 0.000001) between apo A-IV-2 allele frequency and the prevalence of adult lactase persistence. Apo A-IV-2 allele frequency was highest in Iceland, an ancient Viking colony, and decreased across Europe in a north-to-south and west-to-east gradient, generally following hypothetical isoclines for the lactase persistence gene. There were no correlations between the population frequencies of the apo E2, E3, or E4 alleles and either the prevalence of lactase persistence or the frequency of the apo A-IV-2 allele. In light of the effects of the apo A-IV-2 polymorphism on lipid metabolism, we speculate that the apo A-IV-2 allele may have originated in ancient Scandinavia, spread by conferring a nutritional advantage in the setting of a lifelong high milkfat intake, and was later carried southwards by the Viking incursions into Europe.

Influence of APOH protein polymorphism on apoH levels in normal and diabetic subjects

Apolipoprotein (apo)H (also known as beta 2 glycoprotein-I) is a glycoprotein synthesized by liver cells and it is present in the blood associated with plasma lipoproteins. APOH displays a genetically determined structural polymorphism: three alleles (APOH*1, APOH*2, APOH*3) at a single locus on chromosome 17 code for different isoforms, and population studies have shown that APOH*2 is the most frequent allele. This paper assesses the relation between APOH phenotypes and plasma apoH levels in a population composed of 278 healthy subjects (243 H2/2, 32 H3/2, 2 H3/3, 1 H2/1; allele frequencies APOH*1 0.002, APOH*2 0.934, APOH*3 0.064) and 245 diabetics (212 H2/2, 30 H3/2, 3 H3/3; allele frequencies APOH*2 0.927 and APOH*3 0.073). Determination of apoH levels by competitive ELISA gave a mean value of 26.3 +/- 9.8 mg/dl for all subjects, 22.6 +/- 7.7 in normals vs 30.6 +/- 10.3 in diabetics (p = 0.0001), and 23.0 +/- 7.9, 19.3 +/- 5.4 and 18.5 +/- 3.5 mg/dl for H2/2, H3/2 and H3/3 in normals and 31.1 +/- 10.1, 28.2 +/- 10.8 and 15.7 +/- 9.0 mg/dl in diabetics, respectively. ANCOVA of the adjusted data revealed a significant difference in apoH levels for the three phenotypes in both the normal subjects (p = 0.01) and the diabetics (p = 0.02). ANCOVA of the whole samples of subjects, controlling for diabetes as well as age, sex and total cholesterol, indicated a substantial effect of phenotype, independent of the other variables (p = 0.0007).

Social status, social context, and arterial blood pressure

As social change and economic development have proceeded, the prevalence of chronic diseases, especially cardiovascular diseases, has increased in the developing world. In part this is due to the adoption of diets and other health behaviors characteristics of industrialized nations; in part it is a function of changing social and economic circumstances. In this paper, we describe the development and testing of a model designed to account for social and economic effects on cardiovascular disease risk. The model incorporates the fact that global economic processes have made a lifestyle characterized by the consumption of Euroamerican material goods and information a basis for the assignment of social status in local communities. But economic change at the local level is rarely sufficient to provide a foundation for individuals' status aspirations. Hence, many individuals attempt to maintain lifestyle inconsistent with their economic standing, a variable we term lifestyle incongruity. Here we described how this factor is associated with higher blood pressure in a variety of settings and also how the effects of lifestyle incongruity can be modified in local contexts by social class and social role processes. This latter process, contextual modification, is illustrated by data from American Samoa. In this example, the association of lifestyle incongruity with blood pressure is examined in 30 male household heads and 26 spouses. After an examination of Samoan ethnography focused attention on the importance of age and gender differences as defining social contexts of intracultural variation, the model was modified to assess interactions between age and gender as they affect the association of lifestyle incongruity and blood pressure. Lifestyle incongruity is strongly associated with higher systolic and diastolic blood pressure for the younger household heads, minimally associated with blood pressure for older household heads, and only slightly associated with blood pressure of their spouses. The regression coefficients for the lifestyle incongruity by age by sex interaction term was significant at P < or = 0.01 for both systolic and diastolic blood pressure. The consistency of these results with expectations based on the ethnographic record is emphasized in the interpretation. We feel that the lifestyle incongruity model represents and empirically successful attempt to link global political-economic processes, local social structure, and biological outcomes.

The National Institute on Aging/Alzheimer's Association recommendations on the application of apolipoprotein E genotyping to Alzheimer's disease

In a conference held in Chicago during October 1995, a working group of the National Institute of Aging (NIA) and the Alzheimer's Association (AlzA) drafted consensus recommendations on research and clinical applications of APOE genetic susceptibility testing for Alzheimer's disease (AD). The NIA/AlzA Working Group concluded that in considering future applications of APOE genotyping and other knowledge that has been gained about the genetic basis of AD, the interests of AD patients and their family members must be held paramount. The group acknowledged that a robust association exists between possession of the APOE epsilon 4 allele and the risk of late-onset AD and cited evidence that this allele is more strongly associated with AD than any other form of dementia. They recommended against the use of APOE genotyping to predict the-future development of AD in asymptomatic individuals at this time, and warned against the use of the test in isolation as the sole means for diagnosing AD. The group endorsed the concept of discretionary use of APOE genotyping as an adjunct to other AD diagnostic procedures. However, routine clinical use of the test for this purpose was not recommended at this time. Physicians were advised to weigh any potential benefits of testing against the possibility that genotype disclosure could adversely affect the insurability, employability, and social standing of AD patients and their family members. Adequate provisions for pre-test and post-test counseling and psychosocial support were advised for all future clinical and research applications of APOE genotyping. The group called for the development of improved protocols for AD genetic counseling as well as supplemental measures to assure genetic privacy for AD patients and their family members.

Apolipoprotein E Genotyping in Turkish Myocardial Infarction Survivors and Healthy Controls

The apolipoprotein (Apo) E gene is known to be polymorphic. Three common alleles determine six phenotypes which can easily be detected by restriction fragment length polymorphism. We performed apo E genotyping in myocardial infarction survivors and healthy controls for the first time in the Turkish population. DNA was amplified by polymerase chain reaction (PCR) and the PCR product was digested with restriction enzymes HhaI to detect apo E2, E3, E4 and with TaqI to detect apo E1. Relative allele frequency for the patient group was found to be 0.91 for E3, 0.07 for E2, 0.02 for E4 and for the control group 0.875 for E3, 0.067 for E2, 0.058 for E4. Copyright 1995 S. Karger AG, Basel

ApoA-IV phenotype affects diet-induced plasma LDL cholesterol lowering

The National Cholesterol Education Program (NCEP) recommends that dietary total fat, saturated fat, and cholesterol intake be reduced to < or = 30% of calories, < 10% of calories, and < 300 mg/d, respectively (step 1 diet), in the general population to reduce plasma low-density lipoprotein cholesterol (LDL-C) levels and heart disease risk. We examined the LDL-C-lowering response to such a diet (26% fat, 8% saturated fat, and 201 mg/d cholesterol) compared with an average American diet (39% fat, 15% saturated fat, and 435 mg cholesterol/d) in 153 subjects using diet periods of 4 through 24 weeks for each diet phase. The mean LDL-C reduction was 13% in men (n = 93) and 7% in postmenopausal women (n = 60). The effect of apolipoprotein (apo) A-IV phenotype on responsiveness was examined. LDL-C lowering in men was significantly (P < .005) less (7%) for 17 apoA-IV (1/2) subjects than for 76 apoA-IV (1/1) subjects (16%). In women, 7% lowering was observed in both 12 apoA-IV (1/2) subjects and 48 apoA-IV (1/1) subjects. ApoA-IV phenotype had a significant effect on plasma high-density lipoprotein cholesterol levels during both dietary periods; women carrying the apoA-IV-2 allele had higher levels than those homozygous for the apoA-IV-1 allele. The opposite was true for triglyceride levels, but only during the period when the subjects consumed the high-fat, high-cholesterol diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic heterogeneity of apolipoprotein E and its influence on plasma lipid and lipoprotein levels

Apolipoprotein E (apoE) is one of the major protein constituents of chylomicron and very-low-density lipoprotein (VLDL) remnants and plays a central role as a ligand in the receptor-mediated uptake of these particles by the liver. Including the most common variant, apoE3, 30 apoE variants have been characterized. At present, 14 apoE variants have been found to be associated with familial dysbetalipoproteinemia, a genetic lipid disorder characterized by elevated plasma cholesterol and triglyceride levels and an increased risk for atherosclerosis. Seven apoE variants were found to be associated with other forms of hyperlipoproteinemia. This report presents an overview of all currently known apoE variants and their effects on lipoprotein metabolism.