Homozygous DNA variants in exon 9 of the LDL receptor gene in a Thai patient with primary hypercholesterolemia phenotype.

Mutation in low density lipoprotein (LDL) receptor gene causes an inherited primary hypercholesterolemia namely familial hypercholesterolemia (FH). In this study, 46 Thai patients with primary hypercholesterolemia were screened for mutations in exon 9 of the LDL receptor gene by polymerase chain reaction-restriction fragment length polymorphism (PCR - RFLP). The analysed fragment was 224 bp in length. According to the published cDNA sequence, exon 9 of the LDL receptor gene contains several hypermutable CpG dinucleotides. Three of these sites are Hpa II recognition sites. PCR product of exon 9 obtained from amplification of wild-type DNA sample would yield four fragments after Hpa II digestion. The expected sizes of these restriction fragments were 15, 30, 40 and 139 bp. All normocholesterolemic subjects (n = 33) showed normal RFLP. However, in one patient (72 year old female), abnormal RFLP from Hpa II digestion of the amplified exon 9 was observed, i.e., a fragment of 70 bp and another one smaller than 139 bp. Such RFLP reflects that exon 9 of both alleles of the LDL receptor gene in this patient lost one and gained one Hpa II site. It is interesting that this patient, eventhough harbouring two mutations on both alleles of the LDL receptor gene (presumably homozygous genotype of FH), apparently revealed lipid levels of heterozygous phenotype of FH without symptoms of coronary artery disease. It has yet to be proved whether these genetic variations are disease-related mutations or presumably common DNA polymorphisms.

Screening for mutations in exons encoding the ligand-binding domain of the LDL receptor gene using PCR-CFLP and PCR-SSCP.

Primary hypercholesterolemia includes both monogenic disorders and polygenic conditions. Two well defined monogenic disorders are familial hypercholesterolemia (FH) and familial defective apolipoprotein (apo) B-100 (FDB). Both disorders convey high risk of premature coronary artery disease. FH and FDB are caused by mutations in LDL receptor and apo B-100 genes, respectively. In the present study, mutations in both genes in Thai subjects with primary hypercholesterolemia were screened. For apo B-100 gene, a common mutation R3500Q was screened. This mutation was not observed in the patients (n = 45). For LDL receptor gene, mutations in the exons encoding the ligand-binding domain were screened. By PCR-CFLP analysis, 18 abnormal CFLP patterns in exon 4, the hot spot for mutations, were found in patients (n=45). One of the DNA samples with abnormal CFLP patterns was previously identified and reported as a possible disease-causing mutation, namely D151Y. For the other exons, the screening technique was PCR-SSCP. Abnormal SSCP patterns in DNA samples from patients (n=20) were found as follows, two in exon 3, one in exon 5 and another one in exon 6. Further characterization by DNA sequencing and family studies for these abnormal patterns are underway.

Inexpensive, rapid and convenient PCR-minigel SSCP protocol for polymorphisms and mutations analyses of LDL receptor gene.

Hypercholesterolemia has been recognized as a major risk factor of atherosclerosis and coronary artery disease. The elevation in plasma low density lipoprotein (LDL) cholesterol is frequently due to genetic alteration at the genetic locus specifying the LDL receptors, leading to defective catabolism of LDL. In order to facilitate the molecular diagnosis of LDL receptor disorder, single strand conformation polymorphism (SSCP) analysis of polymerase chain reaction (PCR) amplified genomic DNA fragments has become a simple and sensitive screening method for identification of DNA polymorphisms and mutations in LDL receptor gene prior to DNA sequencing. In addition, SSCP patterns can be detected by silver staining to avoid hazardous radioactive material or other costly nonradioactive detection techniques. However, the original SSCP protocol is generally large-formatted, which is both time and reagents consuming as well as cumbersome. Minigel SSCP protocols have thus been devised but they involve, although commercially available, costly precast gels. We describe here a nonradioactive PCR-minigel SSCP protocol which is sensitive, inexpensive, rapid, reproducible and manually convenient. The results in this study demonstrate that minigel-SSCP (gel size: 10 cm x 7.3 cm x 0.075 cm) can detect conformation polymorphisms in PCR-fragments with a comparative sensitivity to large gel SSCP (gel size: 30 cm x 40 cm x 0.04 cm) as exemplified by the SSCP analyses of exon 13 of the LDL receptor gene. For minigel SSCP, the reagents for gel components and silver staining are reduced approximately 9 times and 10 times, respectively. For electrophoresis, electrical power is also reduced 10 times. This improved technique can become routinely used for molecular diagnosis of LDL receptor defect as well as for other genetic disorders.

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.

Mutation analysis of exon 9 of the LDL receptor gene in Thai subjects with primary hypercholesterolemia.

The low density lipoprotein (LDL) receptor plays an important role in cholesterol homeostasis. A mutation in this gene causes an autosomal codominant disorder, namely familial hypercholesterolemia (FH). In this study, single strand conformation polymorphism (SSCP) analysis was used to screen for mutations in exon 9 of the LDL receptor gene in a group of 45 Thai patients (11 males and 34 females) with primary hypercholesterolemia. The peptide encoded by exon 9 belongs to the epidermal growth factor (EGF) precursor homology domain which is highly conserved in the LDL receptor protein. An abnormal SSCP pattern was observed in one female patient. The same screening strategy was also used to screen DNA samples from 33 normolipidemic subjects. All of these samples showed normal SSCP pattern. By direct DNA sequencing, the underlying mutation in the DNA with abnormal SSCP pattern was identified. The index subject was heterozygous for a T to C transition at nucleotide 1235. This transition would cause a nonconservative substitution of a nonpolar side chain amino acid "methionine" at codon 391, with an uncharged polar side chain amino acid "threonine", note M391T. From multiple amino acid sequence alignment in six species, the amino acid at codon 391 and the others nearby are completely conserved. Such nonconservative substitution of an amino acid residue in a highly conserved region could consequently result in a functional and/or structural defect in the receptor protein. In conclusion, we propose that M391T is likely to be the cause of hypercholesterolemia in this index subject.

Screening for a D9N common mutation in exon 2 of the LPL gene in Thai normolipidemic and hyperlipidemic subjects.

Lipoprotein lipase (LPL) is a multifunctional protein, playing a major role in the hydrolysis of triglyceride-rich lipoproteins. It also affects the maturation of high density lipoprotein (HDL) and low density lipoprotein (LDL). A D9N substitution is a frequent mutation found in exon 2 of the LPL gene. It is due to a G --> A transition causing a substitution of Asp by Asn at amino acid residue 9 of the protein. This mutation was screened for in 94 Thai primary dyslipidemic (46 hypercholesterolemic and 48 combined hyperlipidemic) subjects compared to 32 normal healthy subjects using PCR-RFLP. Such a mutation has not, yet, been detected in any of these Thai subjects.

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.

Prevalence of dyslipidemia in the elderly in rural areas of Thailand.

Dyslipidemia is highly prevalent in the urban areas of Thailand but information in the rural area, particularly in the elderly, is limited. The objective of this study was to determine the prevalence of dyslipidemia in the elderly who live in the rural areas of Thailand. Random sampling of the volunteers aged > or = 60 years in 3 districts of Samut Songkhram and Ratchaburi provinces was done. After 12-hour fast, the blood sampling was drawn for the analysis of total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) cholesterol. Eighty men and 123 women, aged 60-87 years old, were included in the study. Mean serum lipid levels of cholesterol, LDL cholesterol, HDL cholesterol and triglycerides were 261.74+/-47.58, 180.35+/-45.06, 43.72+/-12.06, and 188.38+/-103.84 mg/dl respectively. Women had significantly higher body mass index, cholesterol and LDL cholesterol levels than men. Seventy percent of them had cholesterol > or = 240 mg/dl and LDL cholesterol > or = 160 mg/dl. Twenty-five percent had HDL cholesterol < or = 35 mg/dl. However, LDL/HDL cholesterol ratio > 5 which indicated high risk for coronary heart disease were found in only 34%. In conclusion, prevalence of dyslipidemia was very high in Thai rural elderly. Further surveillance in this population is essential in verifying the impact of dyslipidemia as a risk of cardiovascular disease in Thai elderly people.

Relationships of vitamin B1, B12, folate and the cognitive ability of the Thai rural elderly.

The comparisons of the levels of vitamin B1, B12 and folate between the elderly with good and poor cognitive ability are the goals of this study. 203 subjects enrolled in 3 geriatric centers of Ratchaburi province and nearby were recruited. All the subjects were tested with structured Thai Mini Mental State Examination (TMSE) questionnaire by trained examiners. With the cut off point of 23 out of 30 in TMSE, 31 per cent were designated as poor cognitive group. Radiodilution assay was used to determine the level of serum B12 and red cell folate while the TPP effect was processed by spectrophotometry. The prevalence of vitamin B1, B12 and folate deficiency were 30.2 per cent, 3.8 per cent and 8.2 per cent consecutively. None of the studied vitamin levels was shown to be significantly different between the poor and good cognitive group suggesting no proved indication to the use of vitamin B1, B12 and folate in the healthy elderly with poor cognitive function.

Liver abscess: a clinical study of 222 patients.

The medical records of 222 patients with liver abscess at Siriraj Hospital from 1978 to 1985 were analysed. Amoebic abscess was three times more prevalent than pyogenic abscess. In both groups middle aged males were affected more often than others. The main clinical manifestations were fever, right upper quadrant pain and hepatomegaly. History of colitis in the past, marked leukocytosis, elevation of alkaline phosphatase and a single abscess confined to the right lobe were suggestive of amoebic liver abscess. The presence of concurrent abdominal infection, marked anemia and jaundice were associated with pyogenic abscess. Patients with pyogenic abscess developed complications more often and the case fatality rate was greater than patients with amoebic abscess. Most of the patients were successfully treated with a combination of antimicrobials and drainage.