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K Kontula

Publications and source records attributed to K Kontula.

At least 109 records · Page 6Linked to original sources
PubMed1994

A novel amino acid substitution (His183-->Gln) in exon 5 of the lipoprotein lipase gene results in loss of catalytic activity: phenotypic expression of the mutant gene in a heterozygous state.

We have identified a hitherto unrecognized mutation of the lipoprotein lipase gene (LPL) in a Finnish family with Russian and Swiss ancestors. A single base pair substitution of a guanine for cytosine in codon 183 of exon 5 of the LPL gene results in a change of histidine to glutamine in the mature enzyme protein. Expression of a mutant cDNA construct in COS cells resulted in secretion of inactive LPL enzyme protein confirming the functional significance of the mutation. The proband, a 50-year-old female and her two daughters were all heterozygous for the His183-->Gln mutation. Clinically, the proband was characterized by variable and occasionally severe hypertriglyceridemia, obesity, hypertension, coronary heart disease and non-insulin-dependent diabetes mellitus. The daughters, aged 24 and 19 years, were also obese but had milder hypertriglyceridemia. In conclusion, we have identified a novel LPL mutation that results in the synthesis of an inactive enzyme protein. Although the assessment of a causative link between the mutation and hyperlipidemia awaits further studies, our data suggest that heterozygosity for a functional defect of LPL should be considered in patients presenting with the metabolic dyslipidemic syndrome, "syndrome-X."

Amino Acids↗
PubMed1993

A single-base substitution in exon 6 of the androgen receptor gene causing complete androgen insensitivity: the mutated receptor fails to transactivate but binds to DNA in vitro.

A single-base substitution in the coding region of the androgen receptor (AR) gene caused complete androgen insensitivity in a patient with 46,XY karyotype. The mutation was a T-to-G transition in exon 6 and changed the codon 807 from ATG (methionine) to AGG (arginine) in the hormone-binding domain of the protein. The mutation was inserted into the wild-type human AR cDNA and the resulting cDNA expressed in CV-1 cells. Native and mutated AR proteins synthesized in recipient cells had identical molecular masses. Ligand-binding activity of the mutant receptor was less than 5% of that of the wild-type AR. The mutant's interaction with an androgen-response element in vitro was identical to that of the native aporeceptor; however, it did not transactivate a reporter gene construct in transfected CV-1 cells. Androgen insensitivity in our patient was thus due to altered structure of the receptor's steroid-binding region, which prevented the mutated AR from gaining a transcriptionally active form in vivo.

Adult↗
PubMed1993

Deletion of exon 15 of the LDL receptor gene is associated with a mild form of familial hypercholesterolemia. FH-Espoo.

We describe a mutation of the low-density lipoprotein (LDL) receptor gene, designated familial hypercholesterolemia (FH)-Espoo, which deletes exon 15 of the LDL receptor gene. The mutant receptor is predicted to lack 57 amino acids, including 18 serine and threonine residues, which are the sites of the clustered O-linked sugars of the receptor. Studies on 10 carriers of this gene revealed that FH-Espoo is associated with an exceptionally mild form of FH. Thus, in conditions in which cell proliferation was rendered dependent on the function of LDL receptors, lymphocytes from the patients with the FH-Espoo allele had a growth rate intermediate between those from healthy subjects and patients with the FH-Helsinki gene, a mutation known to abolish LDL receptor function. The in vivo fractional catabolic rate of LDL apolipoprotein B was lower than normal in the two FH-Espoo heterozygotes studied. Although higher than those in healthy controls, the serum LDL cholesterol concentrations in patients with the FH-Espoo gene were significantly lower than those in patients with the FH-Helsinki mutation. The thickness of the Achilles tendons was within the normal limits in subjects with the FH-Espoo gene. Our study suggests that moderate varieties of hypercholesterolemia, ie, those not considered to represent FH, may occasionally be due to subtle LDL receptor gene mutations.

Adolescent↗
PubMed1993

Prevalence of familial hypercholesterolemia among young north Karelian patients with coronary heart disease: a study based on diagnosis by polymerase chain reaction.

Two deletions of the low density lipoprotein (LDL) receptor gene account for about 90% of the mutations that cause familial hypercholesterolemia (FH) in eastern Finland. The FH-Helsinki mutation deletes exons 16, 17 and a portion of exon 18, while the FH-North Karelia allele is characterized by a deletion of seven nucleotides from exon 6 of the LDL receptor gene. We developed a DNA assay based on the use of polymerase chain reaction (PCR) which simultaneously detects both of these mutations. We have screened 90 young (< 45 years) eastern Finns with symptomatic coronary heart disease (CHD) for the presence of these FH genes. One or the other of the mutations was present in 4 out of 55 survivors of acute myocardial infarction (AMI) and 4 out of 35 patients with angina pectoris (AP), but in none of 50 healthy controls of similar age. These data show a relatively high prevalence of confirmed FH in young CHD patients (AMI and MI combined: 8/90, or 9%), and also demonstrate the feasibility of PCR techniques in diagnosis of FH among populations with enrichment of specific types of LDL receptor gene mutations.

Adult↗
PubMed1992

A novel polymorphism of apolipoprotein A-IV is the result of an asparagine to serine substitution at residue 127.

We have identified a hitherto unknown genetic polymorphism of apolipoprotein A-IV (apoA-IV). The molecular basis for this polymorphism is an A to G substitution at nucleotide 1687 resulting in an Asn to Ser change of amino acid 127. The frequencies of the two apoA-IV alleles (designated apoA-IV127Asn and apoA-IV127Ser), determined by Hin c II restriction analysis of PCR amplified exon three of the apoA-IV gene, were 0.788 and 0.212, respectively, in a Finnish population sample. Allele frequencies of another polymorphism due to a Thr to Ser substitution at amino acid 347 were determined using Hinf I restriction analysis. The allele frequencies were 0.823 for apoA-IV347Thr and 0.177 for apoA-IV347Ser. None of the apoA-IV polymorphisms (apoA-IV127:Asn----Ser, apoA-IV347:Thr----Ser and apoA-IV360:Gln----His) had any effect on plasma lipid and lipoprotein concentrations in cohorts of dyslipidemic men and in a population sample of normolipidemic controls. There was also no association between the history of previous myocardial infarction and any of the apoA-IV alleles.

Alleles↗
PubMed1992

Lipoproteins and their genetic variation in subjects with and without angiographically verified coronary artery disease.

To examine the concentration of serum lipoproteins and the association of their genetic variation with the occurrence of coronary artery disease (CAD), composite serum lipoprotein profiles including lipoprotein(a) (Lp[a]), apolipoprotein (apo) E phenotypes, and apo B Xba I genotypes were determined in patients with angiographically verified CAD (CAD+ group, n = 111) and in subjects with no angiographic evidence of CAD (CAD- group, n = 46). In addition, we determined the concentrations of serum lipids, lipoproteins, and apolipoproteins in 96 healthy controls. Both CAD- and CAD+ groups had lower concentrations of apos A-I and A-II but higher concentrations of serum total and very low density lipoprotein triglyceride and very low density lipoprotein cholesterol than did healthy controls. The mean concentrations of serum total and low density lipoprotein cholesterol and the median values of Lp(a) were similar in the CAD+ and CAD- groups, both having higher concentrations of low density lipoprotein cholesterol and apo B than the healthy controls. Irrespective of gender, patients with CAD had significantly lower serum high density lipoprotein cholesterol than did those without CAD (1.48 +/- 0.40 versus 1.16 +/- 0.29 mmol/l, p less than 0.001). In women, the mean serum total and very low density lipoprotein triglyceride concentration was also higher in the CAD+ than in the CAD- group. The frequency of the apo E4 allele (epsilon 4) was significantly higher in the CAD+ group (0.293) than in the CAD- group (0.174; p less than 0.001). The frequencies of the two apo B alleles, X1 (Xba I restriction site absent) and X2 (Xba I restriction site present), were similar in the two groups. Stepwise discriminant analysis revealed that in men, serum high density lipoprotein cholesterol had the highest power to discriminate for CAD. In addition, the concentration of plasma apo B levels and the occurrence of apo E phenotypes were independently associated with CAD in men. In women, the only independent factor associated with CAD after adjustment for beta-blocker and diuretics usage was the concentration of serum triglycerides.

Adult↗
PubMed1992

Diagnosis of heterozygous familial hypercholesterolemia. DNA analysis complements clinical examination and analysis of serum lipid levels.

The concordance of clinical and molecular genetic diagnoses of heterozygous familial hypercholesterolemia (FH) was studied in 65 subjects (10 propositi and 55 first-degree relatives) from 10 families with FH. Nine propositi were carriers of the FH-Helsinki deletion of the low density lipoprotein (LDL) receptor gene, prevalent in the Finnish population, while a new deletion, extending from intron 14 to intron 15 of the LDL receptor gene, was identified in one family. Serum LDL cholesterol levels used in the clinical diagnosis (less than 5.0 mmol/l, not FH; 5.0-5.9 mmol/l, possible FH; greater than or equal to 6.0 mmol/l, FH; limits are 1 mmol/l lower for those less than 18 years) were derived from an authoritative recommendation. Tendon xanthomas constituted an additional criterion. With the DNA analysis as the reference, 55 (85%) subjects could be correctly classified clinically as FH patients or subjects without FH. The remaining 10 subjects were misclassified or were in the "possible FH" category. When the age- and sex-specific 95th percentile LDL cholesterol levels were used instead of the rigid values for both adults and children, the percentage of correct diagnoses rose to 95%. Common genetic polymorphisms of apolipoproteins E and B did not markedly affect LDL cholesterol levels in FH patients, whereas increasing age and obesity were associated with elevated LDL levels. In conclusion, DNA analysis is a valuable adjunct to the diagnosis of FH that is applicable to families with a known mutation of the LDL receptor gene. If DNA methods are not available, age- and sex-specific LDL levels should be used as an aid in the clinical diagnosis of FH.

Adolescent↗
PubMed1992

The familial hypercholesterolemia (FH)-North Karelia mutation of the low density lipoprotein receptor gene deletes seven nucleotides of exon 6 and is a common cause of FH in Finland.

A mutation of the LDL receptor gene very common among Finnish patients with heterozygous familial hypercholesterolemia (FH) was identified. This mutation, designated as FH-North Karelia, deletes seven nucleotides from exon 6 of the LDL receptor gene, causes a translational frameshift, and is predicted to result in a truncated receptor protein. Only minute quantities of mRNA corresponding to the deleted gene were detected. Functional studies using cultured fibroblasts from the patients revealed that the FH-North Karelia gene is associated with a receptor-negative (or binding-defective) phenotype of FH. Carriers of the FH-North Karelia gene showed a typical xanthomatous form of FH, with mean serum total and LDL cholesterol levels of 12 and 10 mmol/liter, respectively. This mutation was found in 69 (34%) out of 201 nonrelated Finnish FH patients and was especially abundant (prevalence 79%) in patients from the eastern Finland. These results, combined with our earlier data on another LDL receptor gene deletion (FH-Helsinki), demonstrate that two "Finnish-type" mutant LDL receptor genes make up about two thirds of FH mutations in this country, reflecting a founder gene effect. This background provides good possibilities to examine whether genetic heterogeneity affects the clinical presentation or responsiveness to therapeutic interventions in FH.

Alleles↗
PubMed1992

Molecular genetics of familial hypercholesterolaemia: common and rare mutations of the low density lipoprotein receptor gene.

Mutations of the low density lipoprotein (LDL) receptor gene give rise to familial hypercholesterolaemia (FH), one of the most common single-gene diseases in the world. Approximately 150 different LDL receptor gene mutations have been reported until now and the list seems to be continuously growing. Although hampering molecular genetic diagnosis of FH, this wide variability at the DNA level provides a useful tool to population genetics and may ultimately lead to better understanding of the variation in disease manifestations from family to family. The Finns are among the few populations in which one or two mutant LDL receptor genes explain the majority of FH cases. Either of the two 'Finnish-type' LDL receptor gene deletions, FH-Helsinki or FH-North Karelia, is present in more than 60% of the Finnish FH patients; there are no reports on their existence in other ethnic groups. Assays for these mutations were shown to markedly complement clinical diagnosis of FH in Finland.

Adolescent↗
PubMed1991

Screening for a prevalent LDL receptor mutation in patients with severe hypercholesterolaemia.

A rapid new method for the diagnosis of familial hypercholesterolaemia (FH) detects the deletion extending from intron 15 to exon 18 in the low density lipoprotein (LDL) receptor gene, i.e. the FH-Helsinki mutation responsible for a major portion of FH in Finland. Amplification of the DNA sequences flanking the deletion in the mutant allele generated an abnormal 391-bp product that could be detected by photographing the ethidium-bromide-stained agarose gel after electrophoresis. Up to 50 samples can be analysed in about 8 h. The method was validated by comparison with a routine Southern blot technique. The deletion was found in 23 out of 37 patients with a clinical diagnosis of FH (62%) and in 2 out of 73 with primary hypercholesterolaemia without a clinical diagnosis of FH within a series of 110 consecutive patients with severe hypercholesterolaemia (serum cholesterol greater than 8 mmol/l). The data indicate that DNA techniques may provide a supplementary aid for the routine diagnosis of FH and suggest that the polymerase chain reaction in particular may offer major advantages because of its simplicity and rapidity.

Adult↗
PubMed1991

Polymorphisms of the gene encoding cholesterol ester transfer protein and serum lipoprotein levels in subjects with and without coronary heart disease.

We determined TaqI-A, TaqI-B and EcoNI genotypes at the cholesteryl ester transfer protein (CETP) locus in 111 healthy volunteers and in 187 hyperlipidemic men of whom 72 had suffered a myocardial infarction. There were no significant differences in the allele distributions at these polymorphic loci either between the population sample and the hyperlipidemic subjects, or between patients with and without previous myocardial infarction. To detect the associations between the CETP polymorphisms and serum lipid and apoprotein levels, we determined the serum concentrations of total cholesterol, triglycerides, high density lipoprotein (HDL)-cholesterol, apoA-I, apoA-II and apoB in the subjects studied and correlated them to the 3 RFLPs. No significant differences were observed in the serum levels of apoproteins and lipid parameters between subjects with different genotypes in any of these polymorphic CETP loci, either in the population sample or in hyperlipidemic men. Multivariate analyses did not reveal a significant independent role for any of the 3 polymorphisms in determining serum HDL-cholesterol or apoA-I levels after adjusting for triglyceride and low density lipoprotein cholesterol concentrations. This was evident for the group of healthy volunteers and for hyperlipidemic subjects, including those who had survived a myocardial infarction. We conclude that, in Finns, the CETP RFLPs are not useful markers for the risk of coronary heart disease.

Adult↗