A search for genetic variation in the human apolipoprotein B and A-I genes for use in the study of the genetic epidemiology of atherosclerosis
The genes coding for apolipoproteins B and A-I (apoB and apoA-I) are potential candidate loci for studying heritable determinants of lipid levels, a primary risk factor for development of atherosclerotic vascular disease. A preliminary step in genetic epidemiological analysis is the detection of common genetic variants of a candidate gene for use in subsequent population association studies. This study set out to develop techniques to identify common genetic variants at both the apoB and apoA-I loci. The apoB gene was investigated at the protein level by high resolution electrophoretic techniques, in particular isoelectric focusing (IEF). Although an apparently successful technique was developed producing highly resolved bands, evidence is presented demonstrating that the banding pattern possibly represents artefact resulting from an interaction of apoB with components of the IEF system. Despite exhaustive investigation into possible means of overcoming this problem, including cleavage of apoB by thrombin into smaller fragments, it was concluded that the application of IEF to apoB is not practicable as a means of detecting genetically derived variants suitable for subsequent association studies. The apoA-I gene was investigated at the DNA level by the Polymerase Chain Reaction (PCR) followed by direct sequencing. This technique has yielded three variants in the 5' end of the gene; i) A G to A transition at -75 (GA-75AI) from the initiation of transcription, ii) a C to T transition at &'43 83 (CT&'43 83AI) and iii) a second G to A at &'43 84 (GA&'43 84AI). The frequency of each of these polymorphisms was determined in five populations. Firstly, the 'Glasgow' population, comprising 89 males and 98 females for which a previously compiled data base of lipoprotein and life-style variables was available. This population was used to determine the effects of genotype on lipoprotein parameters separately for males and females. The four other populations comprised a case/control study whereby the frequency of each polymorphism was compared between a healthy control population from Aberdeen and three diseased populations, a) Aberdeen female myocardial infarction survivors (AMI) consisting of 69 individuals, b) Aberdeen dyslipidaemic Hypertensives (ADH) consisting of 25 males and 17 females c) Aberdeen hyperlipidaemia(AH) consisting of 29 males and 29 females.