K. E. Berge

Insertion/deletion (I/D) polymorphism at the locus for angiotensin I-converting enzyme and myocardial infarction.

Bøhn M, Berge KE, Bakken A, Erikssen J, Berg K. Insertion/deletion (I/D) polymorphism at the locus for angiotensin I‐converting enzyme and myocardial infarction.

Insertion/deletion (I/D) polymorphism at the locus for angiotensin I-converting enzyme and parental history of myocardial infarction

Bøhn M, Berge KE, Bakken A, Erikssen J, Berg K. Insertion/deletion (I/D) polymorphism at the locus for angiotensin I‐converting enzyme and parental history of myocardial infarction.

A DNA polymorphism at the angiotensin II type 1 receptor (AT1R) locus and myocardial infarction.

Two hundred and thirty‐five survivors of myocardial infarction (MI) were compared to 384 controls with respect to distribution of genotypes and gene frequencies in the A1166C polymorphism at the angiotensin II type 1 receptor (AT1R) locus. No differences in allele frequencies or genotype distribution were observed when all patients were compared with all controls. When comparing CC homozygotes with the combined group of CA heterozygotes and AA homozygotes (CA/AA), a difference in borderline significance between the MI group and controls was observed (p = 0.05). In males alone, this difference was much more pronounced because of the larger proportion of males with the CC genotype in MI cases than in male controls (p = 0.01). No significant differences were observed between female cases and controls. No interaction between the insertion/deletion (I/D) polymorphism at the angiotensin I‐converting enzyme (ACE) locus and the polymorphism at the AT1R locus was detected. When subdividing the subjects into a “low‐risk” and a “high‐risk” group, based on levels of apolipoprotein B (apoB) and body mass index (BMI), and whether or not the person used lipid‐lowering drugs, the frequency of CC homozygotes in male cases of the “low‐risk” group differed significantly compared to the frequency in male controls of the “low‐risk” group (p < 0.001). No differences were observed in females, but the number of “low‐risk” group female cases was low (n = 3). Thus, CC homozygosity appears to be associated with MI in Norwegian males, especially among those with a “low‐risk” phenotype.

Polymorphisms at the angiotensinogen (AGT) and angiotensin II type 1 receptor (AT1R) loci and normal blood pressure

The M235T polymorphism at the angiotensinogen (AGT) locus and the A1166C polymorphism at the angiotensin II type 1 receptor (AT1R) locus have been reported to be associated with hypertension in several populations. We examined these polymorphisms in three samples of healthy Norwegians with respect to normal blood pressure (BP) levels. None of the genotypes defined by the polymorphisms or their combinations were associated with systolic (S) BP (SBP) or diastolic (D) BP (DBP) level. However, there was a trend in all three series that individuals carrying the C allele of the A1166C polymorphism at the AT1R locus (homozygotes as well as heterozygotes) had higher SBP, than AA homozygous individuals. The observation did not reach statistical significance in any of the series. When examining these two polymorphisms with respect to possible variability gene effects on BP in two series of monozygote (MZ) twin pairs, no such effect was detected. We could not detect any interaction between the loci studied with respect to BP level or variability. Thus, neither the AGT locus nor AT1R locus, separately analysed or together, seem to have variability gene effects or definite level gene effects on normal BP.

No effect of a BglI polymorphism at the renin (REN) locus on blood pressure level or variability

We have studied a normal restriction fragment length polymorphism at the renin locus, detected with the restriction enzyme BgII in healthy Norwegians. No association with blood pressure level or variability was found. Thus, the normal genes detected by examination of this restriction fragment length polymorphism at the renin locus have neither “level gene” nor “variability gene” effects on normal blood pressure.

DNA polymorphism at the locus for angiotensinogen I-converting enzyme in Norwegian patients with myocardial infarction and controls

Recently Cambien et al. (1992) reported that homozygosity for the deletion allele (D) in an insertioddeletion (I/D) polymorphism at the locus for angiotensinogen I-converting enzyme (ACE) is significantly more frequent in male myocardial infarction (MI) survivors than in controls. The effect of the gene appeared to be particularly pronounced in a “low-risk” group. The individuals in the “lowrisk” group had plasma apolipoprotein B (apoB) level and body mass index (BMI) value below the median levels in controls (< 125 mg/dl and < 26 kg/ m2), respectively, and they were not receiving treatment with lipid-lowering drugs. The recent report by Tiret et al. (1993), that DD individuals had an excess of parents with fatal MI, indicates that the I / D polymorphism at the ACE locus confers a risk of overt MI. We have examined 234 MI survivors (1 85 males and 49 females) and 366 controls (172 males and 194 females). A history of parental premature MI was recorded in personal interviews. Two males and one female were excluded because they were adoptees, and two males refused to report on parental MI status; thus 229 MI patients (181 males K. E. Bargo’, M. Behn’ and K. Berg’*’ ‘Institute of Medical Genetics, University of Oslo; and ‘Department of Medical Genetics, UllevAl University Hospital, Oslo, Norway

No effect on blood pressure level or variability of polymorphisms in DNA at the locus for atrial natriuretic factor (ANF)

We have examined healthy Norwegians with respect to two restriction fragment length polymorphisms at the locus for atrial natriuretic factor, detectable with the restriction enzymes XhoI and BglI, respectively. No association with systolic or diastolic blood pressure level or variability was found. Thus, the normal genes detected by examination of these restriction fragment length polymorphisms have neither “level gene” nor “variability gene” effects on normal blood pressure.

Analyses of mutations in the human renal kallikrein (hKLKl) gene and their possible relevance to blood pressure regulation and risk of myocardial infarction

The kallikrein‐kinin system is involved in the maintenance of blood pressure (BP), and studies have shown an inverse correlation between BP and urinary kallikrein levels. These and other effects, make the human tissue kallikrein (hKLKl) gene a candidate gene with respect to BP regulation as well as risk of myocardial infarction (MI). By analysis for single‐stranded conformation polymorphisms (SSCPs), patterns consistent with four different variants of the gene were detected and further characterized by DNA sequencing. Three of the variants have not been described before. Two of the polymorphisms changed the codon for an amino acid. Methods based on the polymerase chain reaction (PCR) were developed to analyze these polymorphisms at the hKLKl locus. We found no evidence of association between any genotype in the polymorphisms and normal BP level in two series of healthy, unrelated individuals. In a third series, diastolic BP exhibited a weak association with genotypes in three of the four polymorphisms. Since no such association was detected in the other two series, we conclude that no effect on normal BP level is exerted by variants in the hKLKl as expressed in these polymorphisms. In two series of monozygotic (MZ) twin pairs, there were no differences between genotypes in within‐pair difference in systolic BP or diastolic BP. Finally, no differences in allele frequencies or genotype frequencies in the four polymorphisms at the hKLKl locus were found between a series of young MI survivors and a series of controls. Thus, genes in the four polymorphisms at the hKLKl locus detected by SSCP and DNA sequencing did not exhibit associations with MI. and had neither “level gene” nor “variability gene” effects on normal blood pressure.

Cardiovascular risk factors in people with different genotypes in the insertion/deletion (I/D) polymorphism at the locus for angiotensin I-converting enzyme (ACE)

The deletion (D) allele of an insertion/deletion (I/D) polymorphism at the locus for angiotensin I‐converting enzyme (ACE) has been reported to be an independent risk factor for myocardial infarction (MI), particularly in people lacking traditional risk factors. Furthermore, a borderline association between Lp(a) lipoprotein level and the I/D polymorphism at the ACE locus was reported in one study. We have searched for possible “level gene” or “variability gene” effects of ACE genes on Lp(a) lipoprotein, total cholesterol (TC), high density lipoprotein (HDL) cholesterol (HDLC), low density lipoprotein (LDL) cholesterol (LDLC), triglycerides (TG), apolipoprotein B (apoB), apolipoprotein A‐I (apoA‐I), and body mass index (BMI). None of these variables differed significantly between genotypes in the I/D polymorphism in any of three population samples. A single population sample created by combining the three series, exhibited an insignificant trend towards individuals carrying the D‐allele having a higher level of Lp(a) lipoprotein than those lacking it, and DD homozygotes had a significantly higher Lp(a) lipoprotein level than the combined group of ID/II individuals (p = 0.03). These results may indicate that the D‐allele of the I/D polymorphism at the ACE locus could influence the level of Lp(a) lipoprotein.

Studies on effects of Lp(a) lipoprotein on gene expression in endothelial cells in vitro

The reason(s) for the atherogenic properties of Lp(a) lipoprotein is still unclear, and several mechanisms have been studied. Alterations in gene expression in endothelial cells (ECs) could be important with respect to risk for coronary heart disease (CHD). We have tested the effects of Lp(a) lipoprotein or the apolipoprotein of Lp(a) lipoprotein (apo(a)) on cultured human umbilical vein endothelial cells (HUVECs) with respect to: (1) the level of endothelin‐1 (ET‐1) mRNA; (2) release of ET‐1 into the culture medium; (3) plasminogen activator inhibitor‐1 (PAI‐1) secretion into the culture medium and; (4) total gene expression in HUVECs, examined by a polymerase chain reaction (PCR)‐based technique, differential display‐reverse transcription‐PCR (DD‐RT‐PCR). Lp(a) lipoprotein reduced the level of ET‐1 mRNA as well as the release of ET‐1. The reduction of ET‐1 in the medium was even more pronounced when HUVECs were incubated with apo(a), but we found no effect of apo(a) on ET‐1 mRNA level. Neither Lp(a) lipoprotein nor apo(a) had a significant influence on PAI‐1 secretion. DD‐RT‐PCR revealed 11 fragments that could represent differences between cells exposed or not exposed to Lp(a) lipoprotein. Following subcloning and sequencing, 18 sequences that differed between exposed and unexposed cultures were obtained. Four of the subcloned fragments have up to now been used as a probe for northern blot analyses, and one fragment was confirmed to be regulated by Lp(a) lipoprotein. In conclusion, Lp(a) lipoprotein is shown to control ET‐1 mRNA levels and the function of at least one more gene, the nature of which is unknown.