Effect of Ava II and NcoI polymorphisms at the low density lipoprotein receptor gene on plasma lipid levels in a group of Thai subjects.

The contribution of common genetic variations at the LDL receptor gene in determining interindividual differences in plasma lipid levels in the general population has been observed in several studies. In this study, we employed the PCR-RFLP method to investigate such an effect of the common Ava II (exon 13) and Nco I (exon 18) polymorphisms at the low density lipoprotein (LDL) receptor gene locus in 54 normolipidemic Thai subjects. The mean LDL-C level was slightly higher in the Ava II (+/+) genotype than the other Ava II genotypes. This difference was significant at the 5 per cent level although there were only three homozygotes with Ava II (+/+) genotype. The average effect of Ava II (+) allele was to increase LDL-C level by 6.75 mg/dl. A gene-dosage effect was not observed for this polymorphism. In addition, the subjects with Ava II (+/+) genotype also tended to have high serum total cholesterol and triglyceride and low HDL-C levels. Nco I polymorphism revealed no statistically significant effect on lipid levels in these subjects. However, the subjects with (+) allele tended to have high levels of LDL-C, serum total cholesterol and triglyceride.

Screening for mutations in exon 4 of the LDL receptor gene in Thai subjects with primary hypercholesterolemia: detection of a novel mutation D151Y by PCR-CFLP.

A mutation in low density lipoprotein (LDL) receptor gene causes an autosomal codominant disorder namely familial hypercholesterolemia (FH). Mutations in the LDL receptor gene are very heterogeneous at the DNA levels, occurring in all 18 exons of the gene. However, exon 4 has been found to be the hot spot for mutational events. In this study DNA from 45 Thai subjects with primary hypercholesterolemia was screened for mutations in the hot spot exon 4. The DNA samples were amplified by Polymerase Chain Reaction (PCR) and screened for mutation by Cleavase Fragment Length Polymorphism (CFLP) technique. Identification of mutation was performed by direct sequencing of PCR product. From this screening, one female patient was found to be heterozygous for a novel mutation which was due to a G to T transversion at nucleotide 514. This transversion would change the species-conserved amino acid at codon 151 from charged R group aspatic (GAC) to uncharged R group tyrosine (TAC), termed D151Y. From the same screening strategy, we found that this mutation was absent in 33 healthy normolipidemic subjects. In this index subject, Arg 3500 Gln mutation in apo B-100 gene, causing hypercholesterolemia namely familial defective apo B-100 (FDB), was not found. Therefore, hypercholesterolemia in this index subject was possibly caused by the D151Y mutation in the LDL receptor gene.

Polymorphism of the gene encoding lipoprotein lipase in thai primary hyperlipoproteinemias.

Lipoprotein lipase (LPL) plays a central role in the clearance of very low density lipoprotein (VLDL) and chylomicrons from the circulation. It also affects the maturation of high density lipoprotein (HDL) and low density lipoprotein (LDL). LPL is an important candidate gene in determining the risk factor in metabolic disorders including primary hyperlipidemia. Our study is the first report from Thailand on the characterization of two common DNA polymorphisms, i.e Pvu II and Hind III at introns 6 and 8, respectively of the LPL gene in 94 Thai dyslipidemic subjects compared to 32 normolipidemic subjects using PCR-RFLP. It was observed that the frequencies of the cut and uncut alleles of Pvu II were 0.67 and 0.33 in normolipidemic subjects. Such frequencies were 0.64 and 0.36 in hyperlipidemic subjects. Additionally, the frequencies of the cut and uncut alleles of Hind III were found to be 0.73 and 0.27 in normolipidemic subjects. They were 0.85 and 0.15 in hyperlipidemic subjects. The allele frequencies of the Hind III but not Pvu II polymorphism in hyperlipidemic subjects were significantly different from normolipidemic subjects (p<0.05). The relation between these polymorphisms and lipid traits was not statistically significant (p>0.05).