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ABCG5 and ABCG8 transporters play an important role in the absorption and excretion of sterols. Missence polymorphisms (Gln604Glu in the ABCG5 and Asp19His, Tyr54Cys, Thr400Lys, and Ala632Val in the ABCG8) in these genes have been described. In 131 males and 154 females whose dietary composition markedly changed and lipid parameters decreased over an 8-year follow-up study (total cholesterol decreased from 6.21+/-1.31 mmol/l in 1988 to 5.43+/-1.06 mmol/l in 1996), these polymorphisms were investigated using PCR. Plasma lipid levels and changes in plasma lipid levels were independent of the Gln604Glu polymorphism in ABCG5 and Asp19His and the Ala632Val polymorphisms in ABCG8. The Tyr54Cys polymorphism influenced the degree of reduction in total plasma cholesterol (delta -0.49 mmol/l in Tyr54 homozygotes vs. delta +0.12 mmol/l in Cys54 homozygotes, p<0.04) and LDL-cholesterol (delta -0.57 mmol/l in Tyr54 homozygotes vs. delta +0.04 mmol/l in Cys54 homozygotes, p<0.03) levels between 1988 and 1996 in females, but not in males. Male Thr400 homozygotes exhibited a greater decrease in total cholesterol (delta -0.90 mmol/l vs. delta -0.30 mmol/l, p<0.02) and LDL-cholesterol (delta -0.62 mmol/l vs. delta -0.19 mmol/l, p<0.04) than Lys400 carriers. No such association was observed in females. We conclude that Tyr54Cys and Thr400Lys variations in the ABCG8 gene may play a role in the genetic determination of plasma cholesterol levels and could possibly influence the gender-specific response of plasma cholesterol levels after dietary changes. These polymorphisms are of potential interest as genetic variants that may influence the lipid profile.

The plasma concentrations of cholesterol precursor sterols and plant sterols vary over a 5- to 10-fold range among normolipidemic individuals, and provide indices of the relative rates of cholesterol synthesis and fractional absorption. In the present study, we examined the relative contributions of genetic and environmental factors to variation in the plasma concentrations and sterol-cholesterol ratios of five noncholesterol sterols, including the 5alpha-saturated derivative of cholesterol (cholestanol), two precursors in the cholesterol biosynthesis pathway (desmosterol and lathosterol), and two phytosterols (campesterol and sitosterol). Plasma sterol concentrations were highly stable in 30 individuals measured over a 48 week period. Regression of offspring sterol levels on the parental values indicated that plasma levels of all five noncholesterol sterols were highly heritable. Analysis of monozygotic and dizygotic twin pairs also indicated strong heritability of all five sterols. Two common sequence variations (D19H and T400K) in ABCG8, an ABC half-transporter defective in sitosterolemia, were associated with lower concentrations of plant sterols in parents, and in their offspring.Taken together, these findings indicate that variation in the plasma concentrations of noncholesterol sterols is highly heritable, and that polymorphism in ABCG8 contributes to genetic variation in the plasma concentrations of plant sterols.

We have previously shown correlations between cardiovascular risk factors such as blood pressure (BP), sympathetic nervous system activity, lipids and insulin resistance in young men with elevated screening BP. In the present study we aimed to: (1) compare the genotype distribution and allele frequencies of 11 polymorphisms in seven candidate genes for BP regulation in healthy 21-year-old Caucasian men, between 18 men with normal and 67 men with high screening BP, and (2) evaluate the effect of these polymorphisms in candidate genes on casual BP, BP responses to mental stress or catecholamines and metabolic parameters including insulin sensitivity. There were no differences in genotype distributions or allele frequencies between the subjects with normal and those with high screening BP. Insulin sensitivity was significantly higher in GG homozygotes in the G-261A polymorphism at the alpha 2A-adrenergic receptor (alpha(2A)AR) locus compared to GA heterozygotes (p = 0.007). Subjects who were homozygous both GG in the G-261A polymorphism at the alpha(2A)AR locus and GlyGly in the Arg16Gly polymorphism at the beta2-adrenergic (beta2AR) receptor loci had significantly higher insulin sensitivity and lower catecholamine levels during mental stress than subjects with other genotypes. Subjects who were II homozygous at the angiotensin converting enzyme (ACE) locus and AA homozygous at the angiotensin type I receptor (AT1R) locus had lower BP and a better lipid profile than the rest of the group. Thus, in this explorative study, we report an association between insulin sensitivity and a polymorphism at the alpha(2A)AR locus. We suggest the presence of gene-gene interactions in the renin-angiotensin system and the sympathetic nervous system.

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.

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.

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.

Angiotensin I-converting enzyme (ACE) cleaves angiotensin I to angiotensin II, which is the active component in the renin-angiotensin system (RAS). We have studied an insertion/deletion polymorphism in DNA at the ACE locus. In three different series comprising 140, 90 and 136 unrelated individuals we found no evidence of association between genotypes in this insertion/deletion (I/D) polymorphism and level of systolic or diastolic blood pressure. In two series of 130 and 88 monozygotic (MZ) twin pairs, respectively, there was no difference between genotypes in within-pair variation in systolic or diastolic blood pressure. Thus, in these series of healthy people, neither "level gene" nor "variability gene" effects of this insertion/deletion polymorphism were observed.

Male (n = 185) and female (n = 49) survivors of myocardial infarction (MI) below 56 and 61 years of age, respectively, were compared to 366 controls with respect to distribution of genotypes in an insertion/deletion (ID) polymorphism at the angiotensin I-converting enzyme (ACE) locus. The frequency of the DD genotype (homozygosity for the deletion allele) was significantly lower among male patients than controls (22.7% versus 34.9%, p = 0.011). In a "low-risk" group, defined as having less than the sex-specific, age-adjusted median values of body mass index (BMI) and apolipoprotein B (apoB), respectively, and absence of treatment with lipid-lowering drugs, the prevalence of the DD genotype was not statistically different between male patients and controls. In a male "high-risk" group (those individuals who had not been defined as "low-risk" subjects), the prevalence of the DD genotype was 20.9% in patients and 38.3% in controls (p = 0.002). In women, no significant differences in genotype frequencies between patients and controls were found in the whole sample or in any subgroup. These results appear to be at variance with data reported recently by Cambien et al. (1992). The difference may be due to chance, undetected selection biases, different gene-environment interactions between Norway and France or Ireland, or to preferential loss of DD individuals in our male "high-risk" group.

One hundred and eighty-one male and 48 female myocardial infarction (MI) survivors and 172 male and 194 female controls were studied with respect to a possible association between premature parental MI (before age 61 years in mothers and/or before age 56 years in fathers) and an insertion/deletion (I/D) polymorphism in the gene encoding angiotensin I-converting enzyme (ACE). In the total series, the frequency of premature parental MI was 14% in the DD (homozygotes for the deletion (D) allele) genotypic group, 10.6% in the ID (heterozygotes) genotypic group and 6.1% in the II (homozygotes for the insertion (I) allele) genotypic group. In all males (male MI survivors and male controls combined), and in the total series, there was a significant excess of DD individuals as compared to II individuals among those with a parental history of premature MI (odds ratio 3.1 (p = 0.03) and 3.1 (p = 0.009), respectively). The ACE polymorphism may be an important genetic marker of MI risk and contribute to clustering of premature MI in families.

Renal kallikrein is a component of the kallikrein-kinin-system (KKS). Kallikrein has been shown to cleave the precursor kininogen to release small kinins, which cause vasodilatation, increased diuresis and natriuresis. We have studied a normal restriction fragment length polymorphism (RFLP) at the renal kallikrein locus (KLK1), detectable with the restriction enzyme TaqI. In one series of 167 unrelated individuals we found a trend towards an association between genotypes in this polymorphism and level of diastolic blood pressure (DBP), but in two other series comprising 123 and 213 unrelated individuals, respectively, we found no suggestion of an association. Since the three series did not exhibit a consistent pattern of association between DBP levels and genotypes in this RFLP, we conclude that the association that appeared in one of the series was probably a chance event. There was no difference between genotypes in any of the three series, with respect to systolic blood pressure (SBP). In two series of, respectively, 157 and 120 complete monozygotic (MZ) twin pairs, there was no difference between genotypes with respect to within-pair variation in SBP or DBP. This indicates that normal KLK1 genes, expressed as variants in this RFLP, do not participate in the determination of the limits within which life-style factors may cause blood pressure (BP) changes. We conclude that neither "level gene" effects nor "variability gene" effects at the KLK1 locus are detectable with the polymorphism analyzed, in the Norwegian population.