Björn Mayer

A comprehensive linkage analysis for myocardial infarction and its related risk factors

Coronary artery disease and myocardial infarction (MI) are leading causes of death in the western world. Numerous studies have shown that risk factors such as diabetes mellitus, arterial hypertension and hypercholesterolemia contribute to the development of the disease. Although each risk factor by itself is partly under genetic control, a positive family history is an independent predictor, which suggests that there are additional susceptibility genes. We have scanned the whole genome in 513 families to identify chromosomal regions linked to myocardial infarction and related risk factors that are known to be under genetic control. Here we show, by using variance component analysis and incorporating risk factors, that risk of myocardial infarction maps to a single region on chromosome 14 with a significant lod score of 3.9 (pointwise P=0.00015, genome-wide P<0.05), providing evidence of a principal MI locus. To characterize this locus we analyzed each risk factor by itself. Serum concentrations of lipoprotein (a) show linkage to both the apolipoprotein (a) locus (lod score 26.99) and a new locus on chromosome 1 (lod score 3.8). There is suggestive linkage for diabetes mellitus on chromosome 6 (lod score 2.96), for hypertension on chromosomes 1 and 6, for high-density and low-density lipoprotein cholesterol on chromosomes 1 and 17, and for triglyceride concentrations on chromosome 9. Although some of these risk factors overlap with previously identified loci, none overlaps with the newly identified susceptibility locus for myocardial infarction and coronary artery disease.

Genetics and heritability of coronary artery disease and myocardial infarction

A positive family history is frequently reported by patients with coronary artery disease (CAD) or myocardial infarction. For risk stratification, it is crucial to distinguish between accidental reoccurrence of sporadic cases and cases with a true heritable component of the conditions. A familial predisposition is assumed when a myocardial infarction is diagnosed by a male first degree relative before the 55th year of life or a female first degree relative before the 65th year of life. The current manuscript reviews major studies from which a familial risk of CAD or myocardial infarction can be inferred. Moreover, a brief overview summarizes the current results of molecular genetic research on chromosomal loci and genes relevant for CAD and myocardial infarction.

Association between a polymorphism in the G protein β3 subunit gene (GNB3) with arterial hypertension but not with myocardial infarction

OBJECTIVE A polymorphism at position 825(C-->T) of the G protein beta3 (GNB3) gene was found to be associated with enhanced transmembrane signalling as well as with an increased prevalence of arterial hypertension. The aim of the present study was to further investigate the association of the GNB3 C825T allele status with arterial hypertension in a large population-based sample and its association with specific end organ damage, i.e. myocardial infarction (MI). METHODS Individuals from a population-based sample (n=2052) and patients suffering from premature MI (age at first MI < or = 60 years, n = 606) were studied by questionnaire as well as by physical examination and biochemical analyses. RESULTS In the population-based sample, the prevalence of arterial hypertension (blood pressure > or = 160/95 mmHg and/or antihypertensive medication) was higher in individuals with the TT genotype (41.8%) as compared to heterozygote individuals (36.6%) or those with the CC genotype (32.75%) (P = 0.02). This association was predominantly found in men. Moreover, men without antihypertensive medication carrying the TT genotype showed higher diastolic blood pressure than those carrying the CC genotype (86.5 vs. 83.7 mmHg, P = 0.04). However, the genotype distribution and the allele frequencies were similar in both, the population-based and the MI patient sample. Furthermore, neither the age at the time of MI nor the location of the MI were related to the genotype distribution. Similarly, gender and age stratified analyses did not show any association of the GNB3 genotype and MI. CONCLUSIONS In male individuals from a large population-based sample, the T allele of the GNB3 polymorphism was associated with arterial hypertension. However, the effects of the GNB3 825T allele on blood pressure were small and did not translate to a clinically relevant increase of risk for MI.

Association of Polymorphisms of the Apolipoprotein(a) Gene With Lipoprotein(a) Levels and Myocardial Infarction

Background—Serum lipoprotein(a) [Lp(a)] concentration is largely determined by variability at the apolipoprotein(a) gene locus. Most prominent effects relate to polymorphisms in the promoter (a pentanucleotide [PN] repeat) and coding regions (a kringle IV [K4] repeat), the latter of which also affects Lp(a) particle size. The impact of these polymorphisms on cardiovascular risk is poorly understood. Methods and Results—We studied both polymorphisms and Lp(a) levels in 834 registry-based myocardial infarction (MI) patients (38% women) and 1548 population-based controls. Lp(a) concentrations were inversely related with the numbers of K4 and PN repeats. However, the effect of the PN polymorphism was restricted to subjects producing small Lp(a) particles (≤8 PN 66.1 mg/dL versus >8 PN 8.7 mg/dL;P <0.0001). The odds to present with MI were elevated in individuals producing small Lp(a) particles (≤22 K4 repeats; OR 1.47 for men and 1.69 for women;P< 0.002) and in women with ≤8 PN repeats (OR 1.46, P =0.009). Interestingly, in women, the frequent haplotype with ≤8 PN and ≤22 K4 repeats, which is related to high levels of small Lp(a) particles, resulted in an elevated OR for MI (1.79;P =0.01) independently of Lp(a) serum concentration. Conclusions—The K4 and PN repeat polymorphisms largely explain the high variability of serum Lp(a) levels. A haplotype with ≤8 PN and ≤22 K4 repeats is characterized by high concentrations of small Lp(a) particles. Our observation that this haplotype was associated with MI independently of Lp(a) serum levels may suggest that Lp(a) particle size in addition to its concentration may modulate MI risk in women.

Association between degenerative aortic valve disease and long-term exposure to cardiovascular risk factors: results of the longitudinal population-based KORA/MONICA survey.

AIMS Degenerative aortic valve disease (DAVD), a common finding in the elderly, is associated with an increased risk of death due to cardiovascular causes. Taking advantage of its longitudinal design, this study evaluates the prevalence of DAVD and its temporal associations with long-term exposure to cardiovascular risk factors in the general population. METHODS AND RESULTS We studied 953 subjects (aged 25-74 years) from a random sample of German residents. Risk factors had been determined at a baseline investigation in 1994/95. At a follow-up investigation, 10 years later, standardized echocardiography determined aortic valve morphology and aortic valve area (AVA) as well as left ventricular geometry and function. At the follow-up study, the overall prevalence of DAVD was 28%. In logistic regression models adjusting for traditional cardiovascular risk factors at baseline age (OR 2.0 [1.7-2.3] per 10 years, P < 0.001), active smoking (OR 1.7 [1.1-2.4], P = 0.009) and elevated total cholesterol levels (OR 1.2 [1.1-1.3] per increase of 20 mg/dL, P < 0.001) were significantly related to DAVD at follow-up. Furthermore, age, baseline status of smoking, and total cholesterol level were significant predictors of a smaller AVA at follow-up study. In contrast, hypertension and obesity had no detectable relationship with long-term changes of aortic valve structure. CONCLUSIONS In the general population we observed a high prevalence of DAVD that is associated with long-term exposure to elevated cholesterol levels and active smoking. These findings strengthen the notion that smoking cessation and cholesterol lowering are promising treatment targets for prevention of DAVD.

Evaluation of the Aldosterone Synthase (CYP11B2) Gene Polymorphism in Patients With Myocardial Infarction

Left ventricular remodeling after myocardial infarction involves activation of the renin-angiotensin-aldosterone system. Recently, the biallelic -344T/C polymorphism of the aldosterone synthase gene was associated with increased aldosterone levels, arterial hypertension, diastolic dysfunction, and left ventricular dilatation. We hypothesized that this polymorphism may also affect left ventricular geometry and function after myocardial infarction. By using a standardized questionnaire, as well as anthropometric and echocardiographic measurements, we thus studied 606 patients (533 men and 73 women) who had a myocardial infarction before the age of 60 years. The aldosterone synthase gene polymorphism was analyzed after polymerase chain reaction amplification and restriction enzyme digestion. The results demonstrated that there was no association of the aldosterone synthase gene polymorphism with echocardiographically determined left ventricular dimensions, wall thicknesses, or indexes of systolic or diastolic function. Furthermore, anthropometric data, including blood pressure levels, were balanced between the different genotypes. Finally, the allele frequency was similar for patients with myocardial infarction and a sample group from the normal population (n=1675). The data indicate that the allele status of the aldosterone synthase gene polymorphism is not useful for the identification of patients with myocardial infarction who have impaired left ventricular function or unfavorable remodeling.

Implications of persistent prehypertension for ageing-related changes in left ventricular geometry and function: the MONICA/KORA Augsburg study.

Background It is unclear whether persistent prehypertension causes structural or functional alterations of the heart. Methods We examined echocardiographic data of 1005 adults from a population-based survey at baseline in 1994/1995 and at follow-up in 2004/2005. We compared individuals who had either persistently normal (<120 mmHg systolic and <80 mmHg diastolic, n = 142) or prehypertensive blood pressure (120–139 mmHg or 80–89 mmHg, n = 119) at both examinations using multivariate regression modeling. Results Over 10 years, left ventricular end-diastolic diameters were stable and did not differ between the two groups. However, the prehypertensive blood pressure group displayed more pronounced ageing-related increases of left ventricular wall thickness (+4.7 versus +11.9%, P < 0.001) and left ventricular mass (+8.6 versus +15.7%, P = 0.006). Prehypertension was associated with a raised incidence of left ventricular concentric remodeling (adjusted odds ratio 10.7, 95% confidence interval 2.82–40.4) and left ventricular hypertrophy (adjusted odds ratio 5.33, 1.58–17.9). The ratio of early and late diastolic peak transmitral flow velocities (E/A) decreased by 7.7% in the normal blood pressure versus 15.7% in the prehypertensive blood pressure group (P = 0.003) and at follow-up the ratio of early diastolic peak transmitral flow and early diastolic peak myocardial relaxation velocities (E/EM) was higher (9.1 versus 8.5, P = 0.031) and left atrial size was larger (36.5 versus 35.3 mm, P = 0.024) in the prehypertensive blood pressure group. Finally, the adjusted odds ratio for incident diastolic dysfunction was 2.52 (1.01–6.31) for the prehypertensive blood pressure group. Conclusions Persistent prehypertension accelerates the development of hypertrophy and diastolic dysfunction of the heart.

Signal transducer of inflammation gp130 modulates atherosclerosis in mice and man.

Liver-derived acute phase proteins (APPs) emerged as powerful predictors of cardiovascular disease and cardiovascular events, but their functional role in atherosclerosis remains enigmatic. We report that the gp130 receptor, which is a key component of the inflammatory signaling pathway within hepatocytes, influences the risk of atherosclerosis in a hepatocyte-specific gp130 knockout. Mice on an atherosclerosis-prone genetic background exhibit less aortic atherosclerosis (P < 0.05) with decreased plaque macrophages (P < 0.01). Translating these findings into humans, we show that genetic variation within the human gp130 homologue, interleukin 6 signal transducer (IL6ST), is significantly associated with coronary artery disease (CAD; P < 0.05). We further show a significant association of atherosclerotic disease at the ostium of the coronary arteries (P < 0.005) as a clinically important and heritable subphenotype in a large sample of families with myocardial infarction (MI) and a second independent population–based cohort. Our results reveal a central role of a hepatocyte-specific, gp130-dependent acute phase reaction for plaque development in a murine model of atherosclerosis, and further implicate IL6ST as a genetic susceptibility factor for CAD and MI in humans. Thus, the acute phase reaction should be considered an important target for future drug development in the management of CAD.

Association of a functional polymorphism in the cyp4a11 gene with systolic blood pressure in survivors of myocardial infarction

Objective Survivors of myocardial infarction (MI) are known to have a high prevalence of arterial hypertension which, at the same time, imposes a major risk to such patients. Genetic variants of the arachidonic acid monooxygenase CYP4A11 may result in decreased synthesis of 20-hydroxyeicostatetraenoic acid (20-HETE), experimental hypertension and elevated blood pressure levels in humans. The present study aimed to investigate the impact of the functionally relevant T8590C polymorphism of this gene on blood pressure and the prevalence of hypertension in MI patients. Methods Survivors of MI from the MONICA Augsburg MI registry (n = 560) were studied after a mean of 5.6 years after the acute event. Participants were examined by standardized anthropometric and echocardiographic measurements, as well as genotyping for CYP4A11 T8590C allele status. Results Genotype frequencies in MI patients (TT = 71.8%, CT = 26.2%, CC = 2.0%) did not differ from those in population-based controls (n = 1363; TT = 75.4%, CT = 22.5% and CC = 2.1%, P = 0.22). MI survivors with the CC genotype displayed higher systolic blood pressure levels (CC: 143.4 ± 4.9 mmHg versus CT: 134.5 ± 1.3 mmHg and TT: 131.1 ± 0.8 mmHg; P = 0.02) and a non-significant trend towards higher diastolic blood pressure levels (CC: 88.4 ± 3.0 mmHg versus CT: 84.9 ± 0.8 mmHg and TT: 83.9 ± 0.5 mmHg; P = 0.17) in multivariate models. Accordingly, the C allele was related to elevated odds ratios for hypertension in a recessive [4.14; 95% confidence interval (CI) = 1.07–15.96, P = 0.04] and in a dominant model (1.50; 95% CI = 1.03–2.20, P = 0.04), respectively. No blood pressure-independent association of the T8590C polymorphism with echocardiographic parameters of left ventricular function and/or geometry was found. Conclusion The data obtained in the present study strengthen the evidence of an association of the CYP4A11 T8590C polymorphism with blood pressure levels and hypertension prevalence. Particularly, the risk of arterial hypertension is substantially higher in MI patients homozygous for the CC allele. By contrast, no evidence was obtained for an association between this genotype and MI.

Lipoprotein lipase gene polymorphism, cholesterol subfractions and myocardial infarction in large samples of the general population

OBJECTIVE Genetic variants of the lipoprotein lipase gene have been associated with dyslipidemia and coronary artery disease. However, data have been inconsistent and are mainly based on selected predominantly male patient groups. METHODS We evaluated the influence of the HindIII restriction fragment length polymorphism on lipid levels in the general population (1361 participants of a large population-based survey from Augsburg, Germany; 50% women) as well as the association of this polymorphism with the risk of myocardial infarction (MI; genotype frequencies in 1159 patients with documented MI under 60 years of age). RESULTS In the population-based survey, a highly significant association between the frequent H2H2 genotype and unfavorable cholesterol subfraction levels was observed in men and in postmenopausal women whereas no significant association was observed in premenopausal women (uni- and multivariate analysis). Such unfavorable lipid levels in homozygotes for the H2 allele may be expected to be associated with a 19-25% increased risk to suffer from myocardial infarction (MI). Nevertheless, genotype and allele frequencies in the general population were not different from those in patients with previous MI (H2H2 genotype frequency 51.3% vs. 53.2%, respectively; P=0.63). CONCLUSION This large study shows that the H2H2 genotype of the lipoprotein lipase gene polymorphism is associated with unfavorable lipid levels. Estrogen status may modulate this association in women. The effects of the genotype on lipid levels were apparently not strong enough to reveal a significant association with MI.