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Biomedical subjects

S Tonstad

Publications and source records attributed to S Tonstad.

At least 91 records · Page 5Linked to original sources
PubMed1995

Determinants of lipid levels among children with heterozygous familial hypercholesterolemia in Norway.

Three founder mutations have been discovered among individuals with familial hypercholesterolemia (FH) in Norway: FHElverum and FHSvartor, predicted to be null alleles, and FHC210G, predicted to disrupt the secondary structure of the ligand-binding domain. To clarify the effect of these and other mutations on lipid levels and parental history of premature cardiovascular disease, we examined 164 boys and girls ages 6 to 16 years with heterozygous FH. Among all children, serum cholesterol levels of the FH parent, percent body fat, pubertal stage, and serum cholesterol levels of the non-FH parent, but not apo E polymorphism, were significant determinants of LDL cholesterol levels in a stepwise multiple regression equation and explained 40% (95% confidence interval [Cl], 25% to 55%) of the variance in LDL cholesterol. Among boys, percent body fat, dietary sucrose, and apo E genotype determined 31% (95% CI, 14% to 49%) of the variance in triglyceride levels; whereas among girls, only percent body fat was associated with triglyceride levels. Percent body fat was not associated with LDL cholesterol or triglyceride levels in the FHC210G group. The children's and FH parents' lipid levels and premature cardiovascular disease among parents were similar among the null-allele and defective-protein groups and in those with an undetected mutation. These data confirm that the phenotypic expression of FH in childhood is influenced by modifiable lifestyle characteristics and by genetic factors other than the underlying mutation and raise the possibility that body fatness may interact with genotype in determining lipid levels.

Adolescent↗
PubMed1995

No effect of beta-carotene supplementation on the susceptibility of low density lipoprotein to in vitro oxidation among hypercholesterolaemic, postmenopausal women.

The effect of beta-carotene on the susceptibility of low density lipoprotein (LDL) to oxidative modification was investigated in a double-blind, randomized placebo-controlled study. Hypercholesterolaemic, postmenopausal women were given 30 mg beta-carotene per day (n = 15 subjects) or placebo capsules (n = 15 subjects) for 10 weeks. They were instructed to follow the American Heart Association Step One diet. LDL, isolated before and after treatment was subjected to copper-catalysed lipid peroxidation. There were no significant differences between LDL from the beta-carotene and placebo groups, as assessed by measuring the lag time for formation of conjugated dienes; the rate of formation and the amount of conjugated dienes formed; the amount of lipid peroxides generated; and the relative electrophoretic mobility, at baseline and after treatment. Dietary records showed that the subjects were consuming similar amounts and types of fat. No significant differences were found in the lipid composition and fatty acid pattern of LDL from the two groups. In conclusion, the results indicated that supplementation with beta-carotene in non-smoking, hypercholesterolaemic, postmenopausal women had no protective effect on the susceptibility of LDL to copper-catalysed modification in vitro.

Adult↗
PubMed1995

Identification of the apo B-3500 mutation in the Norwegian population.

Familial defective apolipoprotein B-100 (FDB) is caused by a mutation in codon 3500 of the apo B gene. It is inherited in a co-dominant fashion and is characterized by hypercholesterolaemia. Thus, FDB has similar features to familial hypercholesterolaemia (FH). In order to investigate whether some of the Norwegian subjects diagnosed as having FH actually have FDB, we have screened 208 Norwegian FH heterozygotes for the apo B-3500 mutation. One of the subjects possessed the mutation which was on a haplotype compatible with the mutation-bearing haplotype found in other populations. Although, hypercholesterolaemia segregated with haplotypes both at the apolipoprotein B and low density lipoprotein (LDL) receptor loci in the proband's family, LDL receptor analysis revealed that the proband was not doubly heterozygous for FDB and FH.

Adult↗
PubMed1995

Is dietary intervention effective in post-transplant hyperlipidaemia?

Current therapies for hyperlipidaemia following renal transplantation include modification of dietary fat. We examined the effect of dietary intervention according to the American Heart Association Step One diet on serum lipids and lipoproteins among 26 men and women with post-transplant hyperlipidaemia. Weighed dietary records showed that the intake of total fat decreased from 30 to 27% and the intake of saturated fat decreased from 12 to 8% of total calories. Body-weight remained stable throughout the study. Serum total, LDL and HDL cholesterol levels were unchanged following 12 weeks of therapy. Serum triglyceride levels decreased slightly. The decrease was seen only in participants with a body mass index < 26 kg/m2, compared to those whose body mass index was > or = 26 kg/m2 (0.4 versus 0 mmol/l; P = 0.03). Serum LDL cholesterol and triglyceride levels were significantly correlated with serum creatinine levels. In conclusion, among renal transplant recipients, hyperlipidaemia appears to be partly related to impairment of renal function, and may not be responsive to modification of dietary fat without weight reduction attempted on an outpatient basis.

Adult↗
PubMed1995

The detection and management of dyslipidaemia in children and adolescents.

Previous algorithms regarding treatment of children with dyslipidaemia do not distinguish sufficiently between children at very high risk for cardiovascular disease and those with less exceptional risk. We propose that physicians assess risk, taking into consideration the nature of the genetic disorder, the severity of hypercholesterolaemia and the family history. Screening should be limited to children with suspected familial hypercholesterolaemia. Guidelines for individualized dietary and drug therapy are suggested.

Adolescent↗
PubMed1994

[A comparison between lovastatin and pravastatin--effects on lipids, sleep and quality of life in primary hyperlipidemia].

The efficacy and safety of treatment with recommended doses of lovastatin (20, 40 and 80 mg/day) and pravastatin (10, 20 and 40 mg/day) were compared in 48 men and women with primary hyperlipidemia and LDL-cholesterol > or = 4.1 mmol/l following dietary intervention. Each dose was taken for six weeks in this double-blind, parallel, randomized study. Lovastatin was found to reduce LDL-cholesterol by 22-37% and pravastatin by 18-26%. HDL-cholesterol levels increased and triglyceride levels decreased to the same extent in both groups. The number of patients who reported adverse events in the course of the study was small. No clinically significant changes occurred in laboratory tests, nor in sleep scores obtained from a standardized questionnaire. Neither drug had any effect on the responses to a quality of life screening questionnaire, nor were any significant changes in depressive symptoms seen during the 18 weeks of treatment.

Adult↗
PubMed1994

The effect of the gastrointestinal lipase inhibitor, orlistat, on serum lipids and lipoproteins in patients with primary hyperlipidaemia.

The effect of orlistat, a nonabsorbed inhibitor of gastric and pancreatic lipases, was examined in patients with primary hyperlipidaemia (serum cholesterol > or = 6.2 mmol.l-1 and triglycerides < or = 5.0 mmol.l-1) not responsive to dietary change alone. In a multicentre, randomised, double-blind study, 103 men and 70 women received 30, 90, 180, or 360 mg or orlistat or placebo for 8 weeks. Total and low-density lipoprotein cholesterol levels were reduced by 4% and 5% with 30 mg orlistat, by 7% and 8% with 90 mg orlistat, by 7% and 7% with 180 mg orlistat and by 11% and 10% with 360 mg orlistat compared to placebo. High density lipoprotein cholesterol levels significantly decreased in the 360 mg orlistat group. Triglyceride levels significantly increased in the placebo group but not in the drug groups. Body weight decreased by 1.2 kg with 360 mg orlistat, despite a weight maintenance diet. Decreases in vitamin E and D levels occurred, although both vitamins remained within the normal range. Adverse effects from the gastrointestinal tract were frequent, but led to discontinuation of therapy in only seven patients. Orlistat is a new therapeutic drug for the treatment of hyperlipidaemia that may be particularly useful among overweight patients. Its potential place in therapy will await long-term studies. Vitamin supplementation should be considered during treatment.

Adult↗
PubMed1994

Two founder mutations in the LDL receptor gene in Norwegian familial hypercholesterolemia subjects.

DNA from 20 unrelated familial hypercholesterolemia (FH) subjects were studied by analysis of single-strand conformation polymorphisms (SSCP) for mutations in exon 3 of the low density lipoprotein (LDL) receptor gene. Four different SSCP patterns were observed. The underlying mutations were characterized by DNA sequencing. One pattern represented the wild-type sequence. Another pattern represented a C-->G mutation (FH-Svartor) that changes codon 78 into the amber stop codon. The two other patterns represented heterozygosity and homozygosity, respectively, for a G-->A splice donor mutation (FH-Elverum) in intron 3. Based upon two PCR-based assays, the frequencies of FH-Svartor and FH-Elverum among 267 unrelated FH subjects, were 8% and 25%, respectively. FH Svartor was located on a chromosome with haplotype 3 in all five families where haplotype analysis were performed. FH Elverum was located on haplotype 2 in 16 out of 20 families. The two mutations must be considered founder mutations in the Norwegian population, and their existence will be clinically useful in diagnosing FH. The presence of two founder mutations together with previously published data on the prevalence of FH in Norway, indicate that FH may be a more common disease in Norway than previously thought.

Base Sequence↗
PubMed1994

Familial hypercholesterolaemia caused by a non-sense mutation in codon 329 of the LDL receptor gene.

Analysis of single-strand conformation polymorphisms (SSCP) was employed to screen familial hypercholesterolaemia (FH) subjects for point mutations in exon 7 of the low density lipoprotein receptor (LDLR) gene. An abnormal band pattern was found in one out of 100 unrelated FH subjects. The underlying mutation was found by DNA sequencing to be due to heterozygosity (C/T) at nucleotide 1048. Nucleotide 1048 is the first nucleotide of codon 329, and is located within the domain that has a high degree of homology with the precursor for epidermal growth factor. The C-->T transition, referred to as FH-Fossum, changes codon 329 from CGAArg to TGAStop. The mutation is expected to cause a class 1 receptor defect.

Codon↗
PubMed1993

Screening for point mutations in exon 10 of the low density lipoprotein receptor gene by analysis of single-strand conformation polymorphisms: detection of a nonsense mutation-FH469-->Stop.

DNA from 40 unrelated familial hypercholesterolemia (FH) heterozygotes were subjected to analyses of single-strand conformation polymorphisms (SSCPs) of exon 10 of the low density lipoprotein receptor (LDLR) gene. Four different SSCP patterns were observed. The underlying mutations were characterized by DNA sequencing. Three of the patterns represented the three genotypes of a recently described sense mutation in codon 450. A method based upon the polymerase chain reaction (PCR) was developed to analyze this mutation. The frequencies of the wild-type (G at nucleotide 1413) and mutant (A at nucleotide 1413) alleles were 0.56 and 0.44, respectively. The fourth pattern was found in only one FH heterozygote and was caused by heterozygosity at nucleotide 1469 (G/A). Nucleotide 1469 is the second base of codon 469Trp(TGG). The G-->A mutation changes this codon into the amber stop codon, and is referred to as FH469-->Stop. The mutant receptor consists of the amino terminal 468 amino acids. Because the truncated receptor has lost the membrane-spanning domain, it will not be anchored in the cell membrane. FH469-->Stop destroys an AvaII restriction site, and this characteristic was used to develop a PCR method to establish its frequency in Norwegian FH subjects. Two out of 204 (1%) unrelated FH heterozygotes possessed the mutation.

Adult↗
PubMed1993

Effectiveness of low-dose lovastatin combined with low-dose colestipol in moderate to severe primary hypercholesterolaemia.

The effect of the combination of low-dose lovastatin and low-dose colestipol was studied among 57 subjects with moderate to severe primary hypercholesterolaemia (total cholesterol > or = 7.0 mmol l-1). Following an 8-week dietary phase, participants were randomized to treatment with 20 mg of lovastatin combined with 5 g or with 10 g of colestipol, or to matching placebo. Baseline total cholesterol was 7.7 +/- 0.9 mmol l-1 after dietary stabilization. Total cholesterol levels were reduced to 5.6 +/- 0.7 mmol l-1 and 5.8 +/- 0.7 mmol l-1 after 4 and 8 weeks of treatment in the lovastatin 5 g-1 colestipol group, and 74% of the subjects achieved the goal of low density lipoprotein (LDL) cholesterol levels of > or = 4.0 mmol l-1. Among the lovastatin 10 g-1 colestipol group, total cholesterol was reduced to 5.4 +/- 0.5 mmol l-1 and 5.5 +/- 0.9 mmol l-1 following 4 and 8 weeks, and 80% of subjects achieved the LDL cholesterol goal. No change was seen in the placebo group. Thus, low-dose combination therapy with lovastatin and colestipol, in conjunction with dietary treatment, is effective in moderate to severe primary hypercholesterolaemia, and is well tolerated.

Adult↗
PubMed1993

Evaluation of running conditions for SSCP analysis: application of SSCP for detection of point mutations in the LDL receptor gene.

We have performed analyses of single-strand conformation polymorphisms (SSCP) of the promoter region and the translated parts of the 18 exons of the low-density lipoprotein receptor (LDLR) gene. DNA from 20 unrelated familial hypercholesterolemia (FH) patients was studied. Four different running conditions were used for the nondenaturing gel electrophoresis to systematically evaluate how differences in the running conditions affect the sensitivity of the assay. These conditions were 15 W, 40 W, and 50 W in the absence of glycerol, and 50 W in the presence of 10% glycerol. SSCP analyses of the 18 PCR fragments for the 20 subjects revealed a total of 46 genotypes at 15 W, 45 at 50 W, 42 at 40 W, and 41 at 50 W with 10% glycerol. A total of 53 different genotypes were observed when the results of the four conditions were considered together. Assuming that the four conditions together detected 100% of the different genotypes, the sensitivity of the four individual conditions ranged between 87% (15 W) and 77% (50 W with 10% glycerol). There were marked differences among the different running conditions to detect abnormal SSCP patterns of individual exons. Therefore, different conditions should be used for the different exons of the LDLR gene.

Base Sequence↗
PubMed1993

Haplotype analysis at the low density lipoprotein receptor locus in normal and familial hypercholesterolemia Norwegian subjects.

We have performed haplotype analysis at the low density lipoprotein receptor (LDLR) locus in order to investigate the molecular genetics of familial hypercholesterolemia (FH) in Norway. Haplotypes were constructed using 7 restriction fragment length polymorphisms (RFLPs) in 194 subjects from 48 unrelated Norwegian FH families. Hypercholesterolemia co-segregated with haplotypes at the LDLR locus in all 48 families. Unambiguous haplotypes could be established for 190 independent chromosomes from 51 FH heterozygotes and 44 healthy normal subjects. A total of 20 different haplotypes was found. The most frequent haplotype was haplotype 3, which accounted for 32.4% or 43.1% of the normal and defective haplotypes, respectively. Haplotype 2 was significantly more frequent among the defective alleles than among the normal alleles (33.3% and 5.8%, respectively, p < 0.0001). Thus, haplotypes 2 and 3 accounted for 76.4% of the defective haplotypes. More data are needed to determine the possible existence of founder genes in the Norwegian population. Haplotypes 1, 2, 3, 5 and 8 accounted for 88.2% of the normal haplotypes. Based upon the cumulative heterozygosity index, the SphI, NcoI and 3' ApaLI RFLPs are the most informative markers in the Norwegian population.

Base Sequence↗
PubMed1992

StyI polymorphism in an enhancer region of the second intron of the apolipoprotein B gene in hyper- and hypocholesterolemic subjects.

The regulation of the human apolipoprotein (apo) B gene that plays a crucial role in lipid metabolism is apparently very complex, with multiple cis- and trans-acting regulatory factors. One of these factors is an enhancer region in the second intron. In this region a point mutation at position + 722 has been found that is detectable by the restriction enzyme StyI. The report of Levy-Wilson et al. (1991) could suggest that the mutant allele (abolished StyI site) is associated with hypocholesterolemia. To investigate further the possible effect of this mutation on plasma cholesterol levels, we have compared the frequency of the mutant allele between 206 hypercholesterolemic Norwegian or Czech subjects on one hand, and 165 hypocholesterolemic Norwegian or Czech subjects on the other hand. No significant difference in frequency was found between the hypercholesterolemic and the hypocholesterolemic groups. This finding indicates either that the mutation at position + 722 does not affect the enhancer activity or that this in vitro enhancer activity is of little or no clinical significance. One of the Norwegian hypercholesterolemic subjects who was of Czech descent possessed the apoB 3500 mutation that leads to defective binding of low density lipoprotein (LDL) to the LDL receptors. Haplotype analysis of the apoB gene in her family showed that the mutation-bearing allele was identical to that reported in other countries, indicating a common gene source.

Adult↗
PubMed1992

A new polymorphism in exon 11 of the LDL receptor gene in healthy people and in familial hypercholesterolemia subjects.

We have screened exon 11 of the low density lipoprotein receptor (LDLR) gene from familial hypercholesterolemia (FH) heterozygotes for point mutations by using analysis of single strand conformation polymorphisms (SSCP). A variant pattern was observed in three out of 39 subjects. By DNA sequencing, this variant pattern was found to be due to a C-->T transition at nucleotide 1617 that affects the third base of codon 518. A PCR method was developed to screen FH heterozygotes and normal subjects for this mutation. The gene frequencies in FH heterozygotes and normal subjects were 4% and 4.5%, respectively. Thus, the mutation cannot be in linkage disequilibrium with a mutation that causes FH. Rather, the mutation may be a useful genetic marker at the LDLR locus. Haplotype analysis at the LDLR locus in two FH families where the proband possessed the mutation revealed that the mutation was on two different haplotypes. This finding is consistent with the mutation occurring at a mutational hot spot.

Base Sequence↗
PubMed1992

A 9.6 kilobase deletion in the low density lipoprotein receptor gene in Norwegian familial hypercholesterolemia subjects.

Haplotype analysis of the low density lipoprotein receptor (LDLR) gene was performed in Norwegian subjects heterozygous for familial hypercholesterolemia (FH). Southern blot analysis of genomic DNA, using an exon 18 specific probe and the restriction enzyme NcoI, showed that two out of 57 unrelated FH subjects had an abnormal 3.6 kb band. Further analyses revealed that this abnormal band was due to a 9.6 kb deletion that included exons 16 and 17. The 5' deletion breakpoint was after 245 bp of intron 15, and the 3' deletion breakpoint was in exon 18 after nucleotide 3390 of cDNA. Thus, both the membrane-spanning and cytoplasmatic domains of the receptor had been deleted. A polymerase chain reaction (PCR) method was developed to identify this deletion among other Norwegian FH subjects. As a result of this screening one additional subject was found out of 124 subjects screened. Thus, three out of 181 (1.7%) unrelated Norwegian FH subject possessed this deletion. The deletion was found on the same haplotype in the three unrelated subjects, suggesting a common mutagenic event. The deletion is identical to a deletion (FH-Helsinki) that is very common among Finnish FH subjects. However, it is not yet known whether the mutations evolved separately in the two countries.

Adolescent↗