Epidemiology of Genetic Factors in Lipid Metabolism

BACKGROUND:

Altered plasma lipid, lipoprotein, and apolipoprotein levels are associated with the occurrence of coronary heart disease, non-insulin dependent diabetes, and gallbladder disease. Although there are many other environmental and biological correlates, clinical, epidemiological, and experimental lines of evidence indicate that lipid metabolism has a central role in the development of coronary heart disease. Evidence pointing to the association between measures of lipid metabolism and other chronic diseases is no less compelling. Non-insulin dependent diabetes mellitus exhibits both the diagnostic abnormal carbohydrate utilization, and altered lipid metabolism. The hypothesis that abnormal lipid metabolism may be causally involved in gallbladder disease is suggested by the presence of cholesterol saturated bile several years prior to the onset of clinically definable gallstones.

Biometrical genetic studies have established that a significant proportion of the fasting plasma lipid, lipoprotein, and apolipoprotein levels is attributable to genetic differences among individuals. Although these studies indicate that polygenetic variability is contributing, they do not yield information about specific candidate genes whose products are involved in the metabolism of the phenotype of interest. Recent advances in molecular biology enable one to measure genetic variability at candidate loci for several risk factors for the common chronic diseases. With this information the contribution of specific candidate genes to polygenetic and phenotypic variability can be estimated. Estimating the effects of specific candidate loci will facilitate the investigation of the interaction between genetic and environmental factors. This study focussed on restriction fragment length polymorphisms in and around the apolipoprotein B gene and on the apolipoprotein E protein polymorphism. The apolipoprotein B and apolipoprotein E genes were selected because of their central role in lipid metabolism and interaction with dietary factors.

DESIGN NARRATIVE:

Using data and blood samples from the 75 nuclear families of Nancy, a determination was made of the effects of apolipoprotein B and E genes on fasting levels of total cholesterol and triglycerides, LDL-cholesterol, HDL-cholesterol, HDL2-cholesterol, HDL3-cholesterol, apo A-I, apo-B, apo C-III, and apo-E. Genetic variability was directly assessed by DNA restriction site variability in the apolipoprotein B gene and by measuring the apolipoprotein E polymorphism. Data collected from these families permitted the partitioning of the effects of the apolipoprotein B and E genes from the overall polygenetic and phenotypic variance of the measured lipids, lipoproteins, and apolipoproteins.