Maternal component in the familial aggregation of hypertension

A descriptive ranking of blood pressure and physical fitness of Latin-American ethnic schoolchildren

BACKGROUND

There is a general lack of information about how insufficient physical activity impacts blood pressure and physical fitness in Latin-American ethnic minorities.

AIMS

To describe the interactions between insufficient physical activity, blood pressure, and physical fitness outcomes in Latin-American schoolchildren of different ethnicity.

METHODS

This was a prospective, international, multi-center, and cross-sectional study of three Latin-American countries involving schoolchildren from seven ethnic groups of Colombia (Tikuna, Nasa, Embera), Brazil (African, Mulato), and Chile (Mapuche), and also European schoolchildren from Brazil and Chile. Data were categorized based on whether participants were physically active (PA) or insufficient physical activity (iPA) using the WHO physical activity recommendations. The main outcomes were systolic (SBP), diastolic (DBP), and mean arterial (MAP) blood pressure, and scores for physical and cardiorespiratory fitness (CRF, by estimated V˙O₂max), handgrip muscle strength (HGS), and standing long jump (SLJ). Secondary outcomes were anthropometric measures (weight, height, body mass index [BMI], waist circumference [WC], waist-to-height ratio), and body fat percentage (BF%, limited data by country). Primary and secondary outcomes were ranked.

RESULTS

For both PA and iPA categories, significant interactions between ethnic groups were found concerning SBP/DBP (F_(37.7), ES 0.08; F_(51.5), ES 0.08), V˙O₂max (F_(37.7), ES 0.08; F_(51.5), ES 0.08), HGS (F_(33.8), ES 0.07; F_(5.03), ES 0.04), and SLJ (F_(64.3), ES 0.14; F_(64.3), 0.14). In the iPA category, Mapuche schoolchildren were classified 1st (119.5; 81.5) with highest SBP/DBP and highest MAP (94.6 mmHg); Embera schoolchildren were classified 1st with lowest V˙O₂max (33.7 mL/kg/min); and European schoolchildren were classified 1st (19.9 kg) with lowest HGS and SLJ (121.4 m) physical fitness.

CONCLUSIONS

Under conditions of insufficient physical activity conditions, Mapuche schoolchildren had the most detrimental blood pressure, whereas Embera, Tikuna, and European schoolchildren had the lowest levels of physical fitness. These results serve to highlight the need for the early and appropriate promotion of physical activity based on ethnic differences in Latin-American schools.

Evaluation of arterial stiffness and central blood pressure by oscillometric method in normotensive offspring of hypertensive parents

Children with a family history of hypertension have higher blood pressure and hypertensive pathophysiological changes begin before clinical findings. Here, the presence of arterial stiffness was investigated using central blood pressure measurement and pulse wave analysis in normotensive children with at least one parent with essential hypertension. Twenty-four-hour ambulatory pulse wave analysis monitoring was performed by oscillometric method in a study group of 112 normotensive children of hypertensive parents aged between 7 and 18 comparing with a control group of 101 age- and gender-matched normotensive children of normotensive parents. Pulse wave velocity, central systolic and diastolic blood pressure, systolic, diastolic and mean arterial blood pressure values were higher in the study group than the control group (p < 0.001, p = 0.002, p = 0.008, p = 0.001, p = 0.005, p = 0.001, p = 0.001, respectively). In all age groups (7-10, 11-14, and 15-18 years), pulse wave velocity was higher in the study group than the control group (p < 0.001). Pulse wave velocity was higher in children whose both parents are hypertensive compared to the children whose only mothers are hypertensive (p = 0.011). Pulse wave velocity values were positively correlated with age, weight, height, and body mass index (p < 0.05). Higher pulse wave velocity, central systolic and diastolic blood pressure values detected in the study group can be considered as early signs of hypertensive vascular changes. Pulse wave analysis can be a reliable, non-invasive, and reproducible method that can allow taking necessary precautions regarding lifestyle to prevent disease and target organ damage by detecting early hypertensive changes in genetically risky children.

Mitochondrial tRNA Mutations Associated With Essential Hypertension: From Molecular Genetics to Function

Essential hypertension (EH) is one of the most common cardiovascular diseases worldwide, entailing a high level of morbidity. EH is a multifactorial disease influenced by both genetic and environmental factors, including mitochondrial DNA (mtDNA) genotype. Previous studies identified mtDNA mutations that are associated with maternally inherited hypertension, including tRNA^Ile m.4263A>G, m.4291T>C, m.4295A>G, tRNA^Met m.4435A>G, tRNA^Ala m.5655A>G, and tRNA^Met/tRNA^Gln m.4401A>G, et al. These mtDNA mutations alter tRNA structure, thereby leading to metabolic disorders. Metabolic defects associated with mitochondrial tRNAs affect protein synthesis, cause oxidative phosphorylation defects, reduced ATP synthesis, and increase production of reactive oxygen species. In this review we discuss known mutations of tRNA genes encoded by mtDNA and the potential mechanisms by which these mutations may contribute to hypertension.

A high prevalence of arterial hypertension in patients with mitochondrial diseases

The prevalence of arterial hypertension in mitochondrial diseases remains unknown. Between January 2000 and May 2014, we retrospectively included patients with genetically proven mitochondrial diseases. We recorded clinical, genetic and cardiac exploration data, including the measure of arterial pressure. Among the 260 patients included in the study (mean age = 44 ± 15 years, women = 158), 108 (41.5%) presented with arterial hypertension. The prevalence of hypertension by sex and age was higher than that observed in the general population for all groups. The prevalence of hypertension was significantly higher in patients with MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes) mutations (66%) and MERRF (myoclonus, epilepsy, ataxia with ragged ref fibres) mutations (61%). In patients with MELAS mutation, the presence of hypertension was significantly associated with age and mutation rate in the blood (odds ratio = 1.12; P = .02) in multivariate analysis. The prevalence of hypertension was more important in patients having a mitochondrial disease. The increased risk was more important in patient with MELAS or MERRF and depended on the rate of heteroplasmy.

Concordance of haemoglobin A1c, blood pressure and C-reactive protein between children and their parents in Chinese households

BACKGROUND

China has the world's highest diabetes prevalence, which along with hypertension and inflammation continues to grow particularly among children. Little is known about the strength of the association of these cardiometabolic risk factors between parents and their children; thus, the potential of household-based strategies to reduce risk is unknown.

OBJECTIVES

The objective of the study is to examine the parent-child association for haemoglobin A1c (HbA1c), blood pressure (BP) and C-reactive protein (CRP) in a large, geographically diverse Chinese sample.

METHODS

In 940 parent-child pairs (children aged 7-17 years) who participated in the 2009 China Health and Nutrition Survey, we measured each individual's HbA1c and CRP using fasting blood and BP. We used sex-specific random-effects linear regression to examine the parent-child association for these risk factors, accounting for within-family clustering.

RESULTS

Child's HbA1c was positively associated with parental HbA1c. Beta coefficients ranged from 0.06 (95% CI 0.03-0.12) for father-daughter to 0.43 (95% CI 0.28-0.58) for mother-son pairs. We also detected a positive mother-daughter association for BP and positive father-child associations for CRP.

CONCLUSION

The statistically significant parent-child association for HbA1c, BP and CRP in Chinese families suggests that household-based interventions could be useful for confronting the high rates of diabetes, hypertension and inflammation in China.

Mitochondrial biogenesis dysfunction and metabolic dysfunction from a novel mitochondrial tRNAMet 4467 C>A mutation in a Han Chinese family with maternally inherited hypertension

To investigate the relationship between mitochondrial DNA (mtDNA) and hypertension as well as the mechanism involved in mitochondrial metabolic dysfunction. We identified a novel tRNAMet C4467A mutation in a Han Chinese family with hypertension. The maternal members presented with increased glucose, total cholesterol, low-density lipoprotein, and serum sodium as well as decreased potassium compared with non-maternal members (P < 0.05). Segregation analysis showed this mutation was maternally inherited. We analyzed lymphocyte cell lines derived from three maternal and three non-maternal family members. Reactive oxygen species production in the mutant cell lines was 114.5% higher compared with that in controls (P < 0.05) while ATP was 26.4% lower. The mitochondrial membrane potential of the mutated cell lines was 26.2% lower than that in controls (P < 0.05). Oxygen consumption rates were decreased in the mutant cell lines (P < 0.05). The activation of caspase-3/7 was 104.1% higher in the mutant cell lines compared with controls (P < 0.05). The expression of voltage-dependent anion channel (VDAC), Bax and apoptosis-inducing factor (AIF) in the mutant cell lines was higher compared with that in controls, with the increased colocalization of VDAC and Bax. Therefore, this mutation contributes to oxidative stress and mitochondrial biogenesis dysfunction, which may be involved in the pathogenesis of hypertension.

[Association of the -844G>A polymorphism in the catalase gene with the increased risk of essential hypertension in smokers]

AIM

To investigate whether the functionally relevant -844G>A promotor polymorphism in the catalase (CAT) gene is associated with the development of essential hypertension (EH).

SUBJECTS AND METHODS

The investigation enrolled 2,339 unrelated ethnic Russian people, including 1,269 EH patients and 770 apparently healthy individuals. Genotyping of CAT -844G>A (rs769214) polymorphism was performed using a TaqMan real-time polymerase chain reaction assay.

RESULTS

The -844A allele (odds ratio (OR)=1.31; 95% confidence interval (CI), 1.04 to 1.64; р=0.02) and the -844AA genotype (OR=1.41; 95% CI, 1.02 to 1.94; р=0.03) were found to be related to a higher risk of EH in the smokers. No association was found between this polymorphism and EH risk in the non-smokers.

CONCLUSION

Smoking is a predisposing factor for development of EH in CAT -844AA genotype carriers.

Mitochondrial tRNA mutations in Chinese hypertensive individuals

PURPOSE

Hypertension is a very important risk factor for cardiac vascular disease. The previous studies showed that mitochondrial DNA mutations are associated with cardiovascular disease, including hypertension.

METHODS

In this study we did systematical analysis on the total 22 mitochondrial tRNAs and the clinical, genetic and molecular changes of 140 Chinese hypertension and 124 controls.

RESULTS

This analysis identified 22 nucleotide changes among 15 different tRNA genes. There are 15 mutations with CI (Conservation index) larger than 75%. Of these, there are 26 patients with CI larger than 75% in the HTN group, higher than the 6 subjects in the control group (P=0.00). The tRNA(Phe) G586A, tRNA(Lys) G8313A and tRNA(His) G12147A mutations create highly conservative base-pairings on the D-stem, tRNA(Lys) G8342A on the T-stem, tRNA(Phe) T616C, tRNA(Ala) T5628C, tRNA(Tyr) G5856A and tRNA(Thr) A15924G on the AC stem, tRNA(Leu(CUN)) G12300A on the AC loop, tRNA(Met) C4467T, tRNA(Trp) T5578C, tRNA(Lys) A8296G, tRNA(Arg) T10463C and tRNA(Thr) C15891T on ACC stem, and tRNA(Ser(UCN)) C7492T on D-A junction, while the other tRNA variants were polymorphisms. The pedigrees of PLAH78 carrying the T5578C, PLAH84 carrying the C4467T, PLAH60 carrying the T5628C and PLAH118 carrying the C7492T mutation exhibited maternal transmission of essential hypertension. Sequence analysis of their mitochondrial genomes revealed the presence of T5578C, C4467T, T5628C or C7492T mutations but the absence of other functionally significant mutations in all matrilineal relatives of these families.

CONCLUSIONS

These tRNAs mutations, associated with altered structures of tRNAs and mitochondrial dysfunction, may contribute to the hypertension in Chinese population. A lot of work still should be done for the mechanism and functional effect of the mtDNA mutation on hypertension.

Systematic analysis of the clinical and biochemical characteristics of maternally inherited hypertension in Chinese Han families associated with mitochondrial

BACKGROUND

Mitochondrial DNA mutations may be associated with cardiovascular disease, including the common cardiac vascular disease, hypertension.

METHODS

In this study we performed segregation analysis and systematically evaluated the entire mitochondrial genome in nine maternally inherited hypertension probands from Chinese Han families. We also performed clinical, genetic and molecular characterization of 74 maternally inherited members from these families and 216 healthy controls.

RESULTS

In the maternally inherited members, 12 had coronary heart disease (CHD), six had cerebrovascular disease, five had diabetes, nine had hyperlipidemia and three had renal disease. Laboratory tests showed that the sodium and potassium levels in blood of the maternally inherited members were higher than those of the control group (P < 0.01), while no differences were observed in fasting blood glucose (FBG), total cholesterol (TC), triglyceride, low density lipoprotein cholesterol (LDL-c) and creatinine levels (P > 0.05). The high density lipoprotein cholesterol (HDL-c) level of the maternally inherited members was lower than that of the control group (P = 0.04). The whole mitochondrial DNA sequence analysis revealed a total of 172 base changes, including 17 in ribosomal RNA (rRNA) genes, four in transfer RNA (tRNA) genes, and 22 amino acid substitutions. The remainder were synonymous changes or were located in non-coding regions. We identified seven amino acid changes in the nine maternally inherited hypertension families, including four mutations in ATPase6 and three in Cytb. More interestingly, tRNA(Ser(UCN)) 7492 T > C was absent in controls and was present in <1% of 2704 mtDNAs, indicating potential functional significance.

CONCLUSIONS

This study showed that mutations in mtDNA may contribute to the pathogenesis of hypertension in these Chinese Han families. In the near future, identification of additional mtDNA mutations may indicate further candidate genes for hypertension.

Increased Prevalence of Hypertension in Young Adults with High Heteroplasmy Levels of the MELAS m.3243A>G Mutation

BACKGROUND

The pathophysiology of hypertension in patients with mitochondrial diseases is different from that of the general population. Growing evidence exists linking mtDNA, its mutations, and mitochondrial dysfunction to the pathogenesis of hypertension. No reports on the prevalence of hypertension in late-onset mtDNA diseases have been described.

METHODS

We performed a retrospective chart review of adult patients with late-onset mtDNA diseases between January 1999 and January 2012 at our center. We grouped them into age categories to allow comparison with previously reported Canadian Health Measures Survey (CHMS) prevalence data.

RESULTS

Twenty-three subjects with hypertension were identified for a crude prevalence of 39.7 % (95 % CI 27-53 %) as compared to the CHMS age-predicted prevalence of 30.5 %. When analyzed by individual age group, there were no significant differences between the observed and the CHMS predicted prevalence rates in the 40 years and older cohorts (age category 40-59, p = 0.63; age category 60-79, p = 0.85). However, hypertension rates were significantly higher than predicted in the under 40 years cohort (55.6 vs. 2.8 %, p < 0.001, CI 21-86 %), in which hypertensive patients with the MELAS m.3243A>G mutation were significantly clustered (p < 0.01). This younger MELAS cohort (n = 4, mean age = 24 years) with hypertension had heteroplasmy levels (mean = 68 %) that were significantly higher than the levels found in the older non-hypertensive MELAS cohort (n = 8, mean age = 52 years, mean = 33 %) (p = 0.04).

CONCLUSION

Relative to age, gender, and mtDNA disease subtype, young adults with high heteroplasmy levels of the MELAS m.3243A>G mutation demonstrate an increased prevalence of hypertension. Further prospective data are needed to confirm this initial finding, which has potentially important treatment implications.

The molecular basis of blood pressure variation

Advances in genetic mapping and sequencing techniques have led to substantial progress in the study of rare monogenic (Mendelian) forms of abnormal blood pressure. Many disease-defining pathways for hypertension have been identified in the past two decades. Perturbations in renal salt handling appear to be a common mechanism underlying these rare syndromes of hypertension. Excess activation at various points in the mineralocorticoid signaling pathway and malfunctioning of the autonomic (specifically sympathetic) nervous system have both been implicated in inducing hypertension, while complementary studies examining low blood pressure phenotypes have identified novel pathways exclusively linked to renal salt wasting in either the thick ascending limb or the distal nephron. The genetic defects and the physiological and cellular pathways affected in these various disorders are reviewed here. Importantly, studies have suggested that genetic variation affecting these same genes and pathways may play an important role in explaining the variation of blood pressure levels in the general population. The investigation of rare syndromes of human blood pressure variation has important implications for improving the diagnosis and treatment of hypertension.

Association of genetic variation in the mitochondrial genome with blood pressure and metabolic traits

Elevated blood pressure (BP) is a major risk factor for cardiovascular disease. Several studies have noted a consistent maternal effect on BP; consequently, mitochondrial DNA variation has become an additional target of investigation of the missing BP heritability. Analyses of common mitochondrial DNA polymorphisms, however, have not found evidence of association with hypertension. To explore associations of uncommon (frequency>5%) mitochon drial DNA variants with BP, we identified uncommon/rare variants through sequencing the entire mitochondrial genome in 32 unrelated individuals with extreme-high BP in the Framingham Heart Study and genotyped 40 mitochondrial single nucleotide polymorphisms in 7219 Framingham Heart Study participants. The nonsynonymous mitochondrial single nucleotide polymorphism 5913G>A (Asp4Asn) in the cytochrome c oxidase subunit 1 of respiratory complex IV demonstrated significant associations with BP and fasting blood glucose (FBG) levels. Individuals with the rare 5913A allele had, on average, 7-mm Hg higher systolic BP at baseline (Pempirical=0.05) and 17-mg/dL higher mean FBG over 25 years of follow-up (Pempirical=0.009). Significant associations with FBG levels were also detected for nonsynonymous mitochondrial single nucleotide polymorphism 3316G>A (Ala4Thr) in the NADH dehydrogenase subunit 1 of complex I. On average, individuals with rare allele 3316A had 17- and 25-mg/dL higher FBG at baseline (Pempirical=0.01) and over 25 years of follow-up (Pempirical=0.007). Our findings provide the first evidence of putative association of variants in the mitochondrial genome with systolic BP and FBG in the general population. Replication in independent samples, however, is needed to confirm these putative associations.

Prevalence and risk factors of hypertension based on repeated measurements in Chinese children and adolescents

OBJECTIVES

This study aimed to determine the prevalence of hypertension from repeated blood pressure (BP) measurements, and examine the association between hypertension and obesity, as well as other related risk factors, in a Chinese pediatric population.

METHODS

A total of 6692 children, aged 3-18 years, were recruited in 2010. Anthropometric measurements and BP were measured using a mercury sphygmomanometer. Those with an elevated BP were screened a second or third time at 2-week intervals. "Hypertension" was defined as elevated BP on all three occasions. A self-administered questionnaire was completed.

RESULTS

The prevalence of an elevated BP was 18.2%, 5.1% and 3.1% on the first, second and third visits, respectively. The odds ratios (ORs) and 95% confidence intervals (CIs) for an elevated BP among obese children were 7.07 (5.94-8.42), 17.23 (12.63-23.52) and 20.63 (13.69-31.09), and among those with a paternal history of hypertension were 1.26 (0.98-1.61), 1.35 (0.90-2.02) and 1.80 (1.15-2.81) on each consecutive visit.

CONCLUSIONS

Repeated measurements are required to confirm the diagnosis of hypertension in children and that obesity and paternal hypertension are strongly associated with pediatric hypertension.

Voltage-dependent anion channel (VDAC) is involved in apoptosis of cell lines carrying the mitochondrial DNA mutation

BACKGROUND

The mitochondrial voltage-dependent anion channel (VDAC) is increasingly implicated in the control of apoptosis. We have studied the effects the mitochondrial DNA (mtDNA) tRNAIle mutation on VDAC expression, localization, and apoptosis.

METHODS

Lymphoblastoid cell lines were derived from 3 symptomatic and 1 asymptomatic members of a family with hypertension associated with the A4263G tRNAIle mutation as well as from control subjects. Mitochondrial potential (DeltaPsim) and apoptosis were measured by flow cytometry; co-localization of VDAC and Bax was evaluated by confocal microscopy.

RESULTS

Expression of VDAC and Bax in mtDNA cell lines was found to be increased compared to controls, while expression of the small conductance calcium-dependant potassium channel (sKCa) was unchanged. Confocal imaging revealed co-localization of VDAC/Bax on the outer mitochondrial membrane of A4263G cell lines but not from controls. Flow cytometry indicated that the mitochondrial potential was decreased by 32% in mutated cells versus controls while rates of apoptosis were increased (P < 0.05). The difference was attenuated by Cyclosporin A (CsA, 2 muM), a blocker of VDAC.

CONCLUSION

We conclude that increased expression of mitochondrial VDAC and subcellular co-localization of VDAC/Bax increases mitochondrial permeability and apoptosis in cell lines carrying the mtDNA tRNAIle A4263G mutation.

The role of mitochondrial genome in essential hypertension in a Chinese Han population

Earlier genetic studies of essential hypertension have focused on nuclear genes or family-based mitochondrial screening in Caucasian and African-American pedigrees. The role of mitochondria in sporadic Chinese hypertensives is unknown. We sequenced mitochondrial genomes in 306 age- and gender-balanced Chinese Han hypertensives and controls. In 153 hypertensives, putative functional changes included 4 changes in rRNA genes, 11 changes in tRNA genes and 25 amino-acid substitutions. The remaining variants were synonymous changes or non-coding regions. In the 153 controls, 2 base changes in the tRNA genes and 13 amino-acid substitutions were found. A8701G in ATP6 gene (belongs to haplogroup M; P=0.0001) and C8414T in ATP8 gene (belongs to haplogroup D; P=0.01) were detected significantly different in the cases and controls. Interestingly, the cases were more likely to have two or more amino-acid changes and RNA variants compared with the controls (57.43 versus 23.81%, P=0.0001). In addition, several variants we found were highly conserved and/or specifically located at the 3' end adjacent to the anticodon, which may contribute to the stabilization of structure, and thus lead to the decrease of tRNA metabolism. In conclusion, mitochondrial SNPs (mtSNPs) may affect the course of hypertension in sporadic Chinese hypertensives. Some specific mtSNP within mitochondria may have potential role in the Chinese hypertensives due to their function. Synergetic interaction between mitochondrial mtSNPs and/or haplogroups is needed to be investigated in the future.

Sex-Specific Familial Clustering of Myocardial Infarction in Patients With Acute Coronary Syndromes

Background— Family history of premature myocardial infarction (MI) in first-degree relatives is a risk factor for MI and an indication for primary prevention. Although excess mother-to-daughter “transmission” occurs in ischemic stroke, no published studies have considered sex-of-parent/sex-of-proband interactions in the heritability of MI.

Methods and Results— In a population-based study (Oxford Vascular Study) of all patients with acute coronary syndromes (ACS), irrespective of age, family history of all acute vascular events and related risk factors were analyzed by sex and age of both probands and first-degree relatives. Premature events were categorized as occurring at age <65 years. Of 835 probands with 1 or more ACS, 623 (420 men) had incident events and complete family history data. In probands with premature ACS, maternal history of both MI and of all vascular events were more common in female than male probands (odds ratio [OR], 2.25; 95% CI, 1.02 to 4.94; P =0.04 and OR, 3.03; 95% CI, 1.47 to 6.26; P =0.002, respectively). No such effect existed for paternal history (OR, 1.00; 95% CI, 0.46 to 2.10; P =0.99 and OR, 1.19; 95% CI, 0.58 to 2.43; P =0.63, respectively). Age at ACS in probands was highly correlated with age at MI in mothers ( r =0.46, P <0.001), regardless of the proband’s sex. Consequently, history of premature maternal MI was strongly associated with premature ACS and premature MI in female (OR, 10.52; 95% CI, 2.17 to 56.6; P =0.001 and OR, 7.31; 95% CI, 1.55 to 34.6; P =0.004, respectively) and male probands (OR, 3.88; 95% CI, 1.20 to 12.6; P =0.01 and OR, 3.63; 95% CI, 1.13 to 11.60; P =0.02, respectively).

Conclusions— Important sex-of-parent/sex-of-proband interactions exist in the family history of MI in patients with ACS. Greater emphasis should be placed on maternal than paternal history of MI, particularly in women aged <65 years.

The molecular sources of reactive oxygen species in hypertension

In both animal models and humans, increased blood pressure has been associated with oxidative stress in the vasculature, i.e. an excessive endothelial production of reactive oxygen species (ROS), which may be both a cause and an effect of hypertension. In addition to NADPH oxidase, the best characterized source of ROS, several other enzymes may contribute to ROS generation, including nitric oxide synthase, lipoxygenases, cyclo-oxygenases, xanthine oxidase and cytochrome P450 enzymes. It has been suggested that also mitochondria could be considered a major source of ROS: in situations of metabolic perturbation, increased mitochondrial ROS generation might trigger endothelial dysfunction, possibly contributing to the development of hypertension. However, the use of antioxidants in the clinical setting induced only limited effects on human hypertension or cardiovascular endpoints. More clinical studies are needed to fully elucidate this so called "oxidative paradox" of hypertension.

Sex Differences in Heritability of Ischemic Stroke

Background and Purpose— Using data from Oxfordshire, UK, we recently showed that women are more likely than men to have a family history of stroke in female versus male first degree relatives. To test the generalizability of this finding, we did a comprehensive systematic review of all available published and unpublished data.

Methods— Studies were included in the present review if they reported the frequency of family history of stroke in relation to sex of parent or proband. Where necessary, we contacted authors of studies to obtain unpublished data. Data from the Oxford Vascular Study (OXVASC) and 3 other Oxford cohorts (1925 patients) were secondarily pooled with the data from other studies.

Results— We obtained data from 18 studies (7941 patients), including unpublished data from 7 studies. Female probands were slightly more likely to have a parental history of stroke than male probands (pooled OR=1.15; 95% CI: 1.03 to 1.29; P (sig) =0.028; P (het) =0.45). Maternal history of stroke was more common than paternal history (pooled OR=1.25; 1.15 to 1.37; P (sig) <0.00001; P (het) =0.12). However, the maternal excess was only present in female probands (pooled OR=1.47; 1.27 to 1.70; P (sig) <0.00001; P (het) =0.11). In contrast, male probands were no more likely to have maternal than paternal history of stroke (pooled OR=1.02; 0.88 to 1.17, P (sig) =0.43; P (het) =0.09).

Conclusions— Women with stroke are more likely than men to have a parental history of stroke, which is accounted for by an excess maternal history of stroke. This finding could be explained by sex-specific genetic, epigenetic, or nongenetic mechanisms.

The genetics of cerebrovascular atherosclerosis

Ischemic stroke attributable to atherosclerosis remains a major public health problem. Genetic factors are increasingly recognized as influencing risk for atherosclerosis directly and indirectly. Genetic makeup may influence the development of major vascular risk factors or alter susceptibility of the cerebral vasculature to these risk factors. More recently, newly identified risk factors for atherosclerosis, such as plasma homocysteine and infection, have also been reported to be influenced by important genetic determinants. This article reviews the current nature on genetics of cerebral and precerebral atherosclerosis and seeks to identify areas of promise for future clinical application.

Maternal influence on blood pressure suggests involvement of mitochondrial DNA in the pathogenesis of hypertension: the Framingham Heart Study

OBJECTIVE

To investigate the contribution of the mitochondrial genome to hypertension and quantitative blood pressure (BP) phenotypes in the Framingham Heart Study cohort, a randomly ascertained, community-based sample.

METHODS

Longitudinal BP values of 6421 participants (mean age, 53 years; 46% men) from 1593 extended families were used for analyses. In analyses of BP as a continuous trait, a variance components model with a variance component for maternal effects was used to estimate the mitochondrial heritability of the long-term average BP adjusted for age, sex, body mass index, and hypertension treatment. For analyses of BP as a categorical trait, a nonparametric test sensitive to excessive maternal inheritance was used to test for mitochondrial effect on long-term hypertension, defined as systolic BP of at least 140 mmHg or diastolic BP of at least 90 mmHg or use of antihypertensive medication in one-half or more of qualifying examinations. This test was based on 353 pedigrees comprised of 403 individuals informative for mitochondrial DNA contribution.

RESULTS

The estimated fraction of hypertensive pedigrees potentially due to mitochondrial effects was 35.2% (95% confidence interval, 27-43%, P < 10). The mitochondrial heritabilities for multivariable-adjusted long-term average systolic BP and diastolic BP were, respectively, 5% (P < 0.02) and 4% (P = 0.11).

CONCLUSION

Our data provide support for a maternal effect on hypertension status and quantitative systolic BP, consistent with mitochondrial influence. Additional studies are warranted to identify mitochondrial DNA variant(s) affecting BP.

Heritability of ischaemic stroke in women compared with men: a genetic epidemiological study

BACKGROUND

Ischaemic stroke is partly heritable. However, although the genetic and non-genetic factors responsible could be sex-specific, interactions between the sex of the parent affected and the sex of the proband or affected siblings are unknown. We sought to assess the relation between the sex and phenotype of affected probands and the sex of affected first-degree relatives.

METHODS

We determined the prevalence of history of stroke in the mother, father, and other first-degree relatives in female and male probands with ischaemic stroke or transient ischaemic attack in the population-based Oxford Vascular Study (OXVASC). We validated our findings using unpublished individual patient data from two independent Oxford studies.

FINDINGS

In OXVASC, detailed family history was available in 806 (93%) probands. Female probands were more likely than males to have at least one affected first-degree relative (146/423 vs 104/383; OR 1.4, 95% CI 1.1-2.0, p=0.02) due entirely to an excess of affected female relatives in female probands (female relative vs male relative OR=1.7, 1.3-2.4, p=0.0004; female only vs male only OR=2.1, 1.4-3.1, p=0.0001). Maternal stroke was more common than paternal stroke in female probands (OR=1.8, 1.2-2.7, p=0.001) but not in males (OR=1.1, 0.7-1.7, p=0.38), and female probands were more likely than males to have an affected sister (OR=3.1, 1.5-6.7, p=0.004) but not an affected brother (OR=1.1, 0.6-2.1, p=0.80). Ages at first stroke were also correlated within families among affected females (r=0.36, p=0.004) but not among affected males, such that the excess of affected female relatives of female probands was greatest when the difference in age at first stroke was less than 5 years (OR=3.7, 1.6-8.6, p=0.0007) and fell as the age difference increased (p for trend=0.004). These findings were independent of traditional risk factors and stroke subtype. Data from the other Oxford studies confirmed the excess maternal history of stroke in female probands (OR=2.3, 1.5-3.8, p<0.00001) and the lack in males (OR=1.0, 0.7-1.4, p=0.58).

INTERPRETATION

Heritability of ischaemic stroke is greater in women than in men, with an excess of affected mothers and affected sisters in female probands independent of traditional vascular risk factors, which could be explained by sex-specific genetic, epigenetic, or non-genetic mechanisms.

Molecular genetics of human hypertension

EH (essential hypertension) is a major public health problem in many countries due to its high prevalence and its association with coronary heart disease, stroke, renal disease, peripheral vascular disease and other disorders. Epidemiological studies have demonstrated that EH is heritable. Owing to the fact that blood pressure is controlled by cardiac output and total peripheral resistance, many molecular pathways are believed to be involved in the disease. In this review, recent genetic studies investigating the molecular basis of EH, including different molecular pathways, will be highlighted.

Association between parental histories of hypertension, diabetes and dyslipidemia and the clustering of these disorders in offspring

BACKGROUND

Familial aggregation of hypertension, diabetes and dyslipidemia has been well reported. However, only a few studies have assessed to what extent parental histories were involved in the clustering of these diseases.

METHOD

In 2002, associations between parental histories of hypertension, diabetes and dyslipidemia and the clustering of high blood pressure, hyperglycemia and dyslipidemia in individuals were assessed on the basis of 5010 Japanese men and women aged 33-66 years. Risk factor clusters were defined as those having at least two of the three clinical disorders.

RESULTS

Compared with persons with no parental history of the three diseases, those who had 1, 2 and 3 or more parental histories had risk factor clusters, 1.25 (95% CI: 1.07, 1.47), 1.46 (95% CI: 1.16, 1.84) and 1.41 (95% CI: 0.95, 2.11) times higher, respectively, after adjusting for confounding factors. ORs by 1, 2 and 3 of maternal history were 1.33 (95% CI: 1.12, 1.58), 1.65 (95% CI: 1.16, 2.35) and 1.69 (95% CI: 0.64, 4.42), respectively (trend P < 0.001). However, the number of paternal history was not associated with risk factor clusters.

CONCLUSION

We conclude that familial history, particularly maternal history, is an important aid to prevention strategy and public health practice for metabolic disorders.

Essential hypertension seems to result from melatonin-induced epigenetic modifications in area postrema

Essential hypertension is a complex multifactorial disorder with epigenetic and environmental factors contributing to its prevalence. Epigenetic system is a genetic regulatory mechanism that allows humans to maintain extraordinarily stable patterns of gene expression over many generations. Sympathetic nervous system plays a major role in the maintenance of hypertension and the rostral ventrolateral medulla is the main source of this sympathetic activation. A possible mechanism to explain the sympathetic hyperactivity in the rostral ventrolateral medulla is an action of the area postrema. Area postrema seems to be the region where a shift of the set-point to a higher operating pressure occurs resulting in hypertension. But, how can a shift occur in the area postrema. We propose that melatonin-induced epigenetic modifications in the neurons of area postrema plays a role in this shift. Area postrema is reported to contain high levels of melatonin receptors that play a role in the epigenetic modifications in certain cells. Environmental stressors cause epigenetic modifications in the neurons of area postrema via the pineal hormone melatonin and these changes lead to a shift in the set-point to a higher operating pressure. This signal is then sent via efferent projections to key medullary sympathetic nuclei in rostral ventrolateral medulla resulting in increases in sympathetic nerve activity. This model may explain the long-term alterations in sympathetic activity in essential hypertension.

N-Domain angiotensin I-Converting enzyme expression in renal artery of Wistar, Wistar kyoto, and spontaneously hypertensive rats

One of the most intriguing features in kidney transplantation is the finding that kidneys from hypertensive rats can transfer arterial hypertension on transplantation into normotensive rats. Some evidence also suggest that, in humans undergoing renal transplantation, the genotype of the donor kidney determines the blood pressure in the recipient. The renin-angiotensin-aldosterone system is the major etiological candidate in hypertension because it plays an important role in the control of cardiovascular homeostasis. Angiotensin-converting enzyme (ACE) cleaves the C-terminal from angiotensin I as well as from bradykinin. Thus, by generating the potent vasoconstrictor angiotensin II and by degrading the vasodepressor bradykinin, ACE is considered to play a role in blood pressure regulation. We have previously described the presence of N-domain ACE in urine of Wistar (W), Wistar Kyoto (WKY), and spontaneously hypertensive rats (SHR), all of which can hydrolyze the vasodilator peptide Angiotensin 1-7 and also the N-Acetyl-Ser-Asp-Lys-Pro, two peptides described as specific for N-domain ACE. These findings suggest that the 90 kd ACE isoform found in urine and in tissues of SHR is a possible genetic marker of hypertension. Based on the fact that the renal artery has an important role in the control of renal blood flow, we evaluated the presence of N-domain ACE in the renal artery of hypertensive and normotensive rats. Using Western blotting techniques on the renal arteries of W and WKY rats, we detected the 190-kd ACE (similar to somatic ACE) and also the 65-kd ACE previously described in urine and renal tissue as N-domain ACE. The 65-kd and 90-kd isoforms of ACE were also detected in renal arteries in SHR rats. Further studies are required to understand the role of 90-kd enzyme described as a possible local marker of hypertension, its contribution in angiotensin catabolism, and whether this abnormal form of the enzyme has any link with the development and transfer of hypertension after transplantation.

Genetics of the kidney and hypertension

Success in the search for genes that cause or contribute to hypertension susceptibility has been limited to a few rare Mendelian forms of hypertension (glucocorticoid remediable aldosteronism, apparent mineralocorticoid excess, and Liddle's syndrome). Our well-reasoned efforts to assess candidate genes in critical pathways known to be involved in blood pressure regulation have not been as productive in complex genetic cases of hypertension. These cases involve both genetic and environmental determinants. The most frequently used approach to the identification of hypertension genes involves genetic association studies, which are population based and compare cases and controls. Linkage analyses are also used but require family data. While much effort is spent identifying new markers and candidate genes, it is important to periodically determine which findings of linkage or association are confirmed in order to advance our quest to identify hypertension genes. In this review, the status of the assessment of the HSD11B2 gene is reviewed. In addition, data supporting the need to assess the mitochondrial genome, the other human genome, in hypertension susceptibility are reviewed.

A novel class of tests for the detection of mitochondrial DNA-mutation involvement in diseases

We develop a novel class of tests to detect mitochondrial DNA (mtDNA)-mutation involvement in complex diseases by the study of affected pedigree members. For a pedigree, affected individuals are first considered and are then connected through their relatives. We construct a reduced pedigree from an original pedigree. Each configuration of a reduced pedigree is given a score, with high scores given to configurations that are consistent with mtDNA-mutation involvement and low scores given to configurations that are not consistent with mtDNA-mutation involvement. For many pedigrees, the weighted sum of scores of the pedigrees is calculated. The tests are formed by comparing the observed score with the expected score under the null hypothesis that only nuclear autosomal mutations are involved. We study the optimality of score functions and weights under the heterogeneity model without phenocopies. We also develop a method to estimate the contribution that mtDNA mutations make if they are involved under a heterogeneity model. Finally, we apply our methods to three data sets: Leber hereditary optic neuropathy, a disease that has been proved to be caused by mtDNA mutations; non-insulin-dependent diabetes mellitus (NIDDM); and hypertension (HTN). We find evidence of mtDNA-mutation involvement in all three diseases. The estimated fraction of patients with NIDDM due to mtDNA-mutation involvement is 22% (95% confidence interval [CI] 6%-38%). The fraction of patients with HTN potentially due to mtDNA-mutation involvement is estimated at 55% (95% CI 45%-65%).

A case-control for the association between change in weight, family history and hypertension at different ages

To study the association between the changes of weight, family history and hypertension at different ages, a pair-matched case-control study was conducted in the outpatient service of department of internal medicine in Binjiang Hospital of Tianjin from 1994 to 1996. The cases were selected from 312 patients with hypertension diagnosed during 1994-1996 and identified newly in the survey. The controls were selected from other outpatients of no cardiovascular disease histories matched by age and sex. The conditional logistic regression model was used. The cases and controls were divided into two age groups under 59 years old, 60 and older. History of hypertension in the first degree-relatives was linked to hypertension, but family history of hypertension of groups under age 59, and at 60 and older was mainly hypertension history of parents and siblings, respectively. Other risk factors of developing hypertension were higher weight or body mass index (kg/m2) in the survey, higher degree of weight gain in comparison with the basic weight and early age at beginning weight gain in all two groups. However, the risk of developing hypertension for increasing weight and obesity increased with advancing age groups. The study further indicates that controlling body weight, decreasing the degree of weight gain, and delaying the beginning age of weight gain all contribute to the lower risk of suffering from hypertension and were effective measures of hypertension of the prevention and cure.