行政院國家科學委員會補助專題研究計畫成果報告

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1 NSC892314B

2 Molecular Study of Type III Hyperlipoproteinemia in Taiwan β β ε E Abstract β Type III hyperlipoproteinemia (type III HLP; familial dysbetalipoproteinemia ) is a condition characterized by elevated serum total cholesterol (TC) and triglyceride (TG) 2

3 levels, and by a cholesterol-enriched very low density lipoprotein (VLDL) designated floating-â lipoprotein or â-vldl. Affected individuals may rarely have yellowish lipid deposits in the creases of the palms of the hands called xanthoma striata palmaris. In addition, eruptive and tuberous xanthomas are occasionally seen. Coronary heart disease and peripheral vascular disease both occur prematurely in type III HLP. More than 90% of the patients are homozygous for apolipoprotein E2 in most populations analyzed thus far. Apolipoprotein E (apoe) is a polypeptide comprised of 299 amino acids found in chylomicrons (CM), VLDL, and high density lipoproteins (HDL). The structure gene for apoe is polymorphic. Three common isoforms of the protein (apoe2, apoe3, apoe4), due to three different alleles (â2, â3, â4) inherited in a codominant fashion, account for six common phenotypes (apoe2/2, apoe2/3, apoe2/4, apoe3/3, apoe3/4, apoe4/4). These isoforms interact differently with specific lipoprotein receptors, and thereby alter circulating lipid levels. When compared with the most common apoe3 isoform, the apoe2 isoform has a significantly reduced affinity for the LDL receptor, this may result in the homozygous state in accumulation of cholesterol-enriched lipoprotein remnants and in some individuals this phenotype is associated with type III hyperlipoproteinemia. The aim of this study was to determine the relationship between apoe genotype and type III HLP patients and to evaluate the apoe genotyping with temperature gradient gel electrophoresis (TGGE). Type III HLP was defined by elevated serum triglyceride and cholesterol concentrations and by the presence of both â-vldl and a ratio of VLDL cholesterol to plasma triglyceride of > The genotype and the allele frequencies of type III HLP were also compared between Taiwanese and other populations. In 10 patients with type III HLP, only two were apoe2/2 homozygous. The â2 allele frequency was 0.5, which indicated that the heterozygotes were the major genotypes. This result was different from that of Caucasian but similar to Japanese. In addition to the common apoe genotype, no other apoe variant was found by direct sequencing. Due to the poor reproducibility, apoe genotyping with temperature gradient gel electrophoresis technique was not feasible and modification of the technique is necessary. Keywords: Type III Hyperlipoproteinemia, Apo E, Gene sequencing, Temperature Gradient Gel Electrophoresis Technique 3

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7 No. SEX F/M AGE TC TG years mg/dl mg/dl HDL-C mg/dl LDL-C mg/dl VLDL-C/TG β-vldl N=10 4/6 63.1± ± ± ± ±15.1 >0.3 + N=6 1/5 64.2± ± ± ± ±34.3 >0.3 - N=27 15/ ± ± ± ± ±9.2 <0.3 + mean±sem 7

8 TC TG HDL-C LDL-C HLP mg/dlmg/dl mg/dl mg/dlvldl-c/tg β-vldl ApoE genotype 26 F /2 77 M /2 110 F /3 119 F /3 195 M /3 268 M /4 283 M /3 304 M /3 329 M /3 366 F /3 (lipoprotein electrophoresis) 8