Genetic Epidemiology of Lipoprotein-Lipid Levels

DESIGN NARRATIVE: Beginning in 1991, genetic variations in the gene products of A-IV, E, H, and APO(a) were determined by isoelectric focusing and SDS/immunoblotting; gene variations at the APOB, D, LDL receptor, hepatic lipase, lipoprotein lipase, and cholesteryl ester transfer protein were assayed by polymerase chain reaction protocols and by using cloned cDNA probes for restriction fragment length polymorphism (RFLP) analyses. Direct haplotype analyses of individuals employed a strategy using RFLP analysis combined with the use of allele specific oligonucleotides. Quantitative levels of apolipoprotein B, E, H and APO (a) were determined by immunological techniques. These data and prior data on levels of triglycerides, total cholesterol, HDL-, LDL- and HDL subfraction cholesterol were used in the quantitative genetic analysis. Estimates of the effect of alleles at each of the genetic loci on the quantitative apolipoprotein and lipoprotein levels employed the measured genotype approach. The effects of multisite haplotypes for RFLPs at various loci were estimated using the same methods. For common alleles in each system, estimates were made of the interaction of alleles at independent genetic loci in determining quantitative variables. Dietary information from the San Luis Valley population was used to estimate cholesterol intake identified. Allelic effects were estimated in these groups to gain insight into the effect of dietary cholesterol intake of the estimated allelic effects. The study was renewed in fiscal year 1996 to determine the contribution of polymorphic variation in nine candidate genes involved in lipid metabolism [APO(a), APOD, hepatic lipase (HL), cholesteryl ester transfer protein (CETP), LDL receptor related protein (LRP), 3- hydroxy-3 methyl glutryl-coenzyme A (HMG COA), VLDL-receptor, Lecithin cholesterol acyletransferase (LCAT) and paraoxonase (PON)] in determining quantitative lipoprotein-lipid levels in Hispanics and non-Hispanic Whites of the San Luis Valley, Colorado. The study also determined the molecular basis of the functional mutation in the lipoprotein lipase (LPL) gene which is associated with plasma triglyceride and HDL cholesterol variations. The objectives were achieved by fulfilling the following specific aims: 1) by PCR, DNA sequencing and SSCP analyses, all coding exons and putative regulatory elements in the LPL gene of individuals who were homozygous for the HindIII restriction site to detect nucleotide changes in the coding region which affected directly triglycerides and HDL-cholesterol levels werescreened, in vitro mutagenesis and expression studies were conducted to confirm which of the putative functional mutations was the actual functional mutation; 2) genetic variations in genes coding for CETP, HL, LRP, APOD, HMG COA, VLDL-receptor, LCAT and PON were identified by PCR or standard Southern blotting techniques, and the impact of individual polymorphisms and the joint impact of polymorphisms at different loci (genotype-genotype interaction) in determining quantitative lipoprotein-lipid levels in Hispanics and non-Hispanic whites were estimated; and 3) the distribution of APO(a) kringle 4 and pentanucleotide polymorphisms were determined by SDS-agarose gel electrophoresis and PCR, respectively, and LP(a) levels were quantified by enzyme-linked immunosorbent assay, and the correlation between APO(a) polymorphisms and LP(a) levels were investigated. The study completion date listed in this record was obtained from the "End Date" entered in the Protocol Registration and Results System (PRS) record.