Genetically determined height and coronary artery disease

BACKGROUND

The nature and underlying mechanisms of an inverse association between adult height and the risk of coronary artery disease (CAD) are unclear.

METHODS

We used a genetic approach to investigate the association between height and CAD, using 180 height-associated genetic variants. We tested the association between a change in genetically determined height of 1 SD (6.5 cm) with the risk of CAD in 65,066 cases and 128,383 controls. Using individual-level genotype data from 18,249 persons, we also examined the risk of CAD associated with the presence of various numbers of height-associated alleles. To identify putative mechanisms, we analyzed whether genetically determined height was associated with known cardiovascular risk factors and performed a pathway analysis of the height-associated genes.

RESULTS

We observed a relative increase of 13.5% (95% confidence interval [CI], 5.4 to 22.1; P<0.001) in the risk of CAD per 1-SD decrease in genetically determined height. There was a graded relationship between the presence of an increased number of height-raising variants and a reduced risk of CAD (odds ratio for height quartile 4 versus quartile 1, 0.74; 95% CI, 0.68 to 0.84; P<0.001). Of the 12 risk factors that we studied, we observed significant associations only with levels of low-density lipoprotein cholesterol and triglycerides (accounting for approximately 30% of the association). We identified several overlapping pathways involving genes associated with both development and atherosclerosis.

CONCLUSIONS

There is a primary association between a genetically determined shorter height and an increased risk of CAD, a link that is partly explained by the association between shorter height and an adverse lipid profile. Shared biologic processes that determine achieved height and the development of atherosclerosis may explain some of the association. (Funded by the British Heart Foundation and others.).

Circulating brain-derived neurotrophic factor concentrations and the risk of cardiovascular disease in the community

Background

Brain‐derived neurotrophic factor (BDNF) is a pleiotropic peptide involved in maintaining endothelial integrity. It is unknown if circulating BDNF levels are associated with risk of cardiovascular disease (CVD).

Methods and Results

We prospectively investigated the association of circulating BDNF levels with cardiovascular events and mortality in 3687 participants (mean age 65 years, 2068 women) from the Framingham Heart Study (FHS). Using a common nonsynonomous single nucleotide polymorphism (SNP) in the BDNF gene (rs6265), we then performed a Mendelian randomization experiment in the CARDIoGRAM (Coronary ARtery DIsease Genome‐Wide Replication And Meta‐Analysis) consortium (>22 000 coronary artery disease [CAD] cases, >60 000 controls) to investigate whether SNP rs6265 was associated with CAD in CARDIoGRAM and, if so, whether the effect estimate differed from that predicted based on FHS data. On follow‐up (median 8.9 years), 467 individuals (261 women) in FHS experienced a CVD event, and 835 (430 women) died. In multivariable‐adjusted Cox regression, serum BDNF was associated inversely with CVD risk (hazard ratio [HR] per 1‐SD increase 0.88, 95% CI 0.80 to 0.97, P=0.01) and with mortality (HR 0.87, 95% CI 0.80 to 0.93, P=0.0002). SNP rs6265 was associated with BDNF concentrations (0.772 ng/mL increase per minor allele copy) in FHS. In CARDIoGRAM, SNP rs6265 was associated with CAD (odds ratio 0.957, 95% CI 0.923 to 0.992), a magnitude consistent with the predicted effect (HR per minor allele copy 0.99, 95% CI 0.98 to 1.0; P=0.06 for difference between predicted and observed effect).

Conclusion

Higher serum BDNF is associated with a decreased risk of CVD and mortality. Mendelian randomization suggests a causal protective role of BDNF in the pathogenesis of CVD.

Genetics of coronary artery disease: an update

In 2007, the first genetic risk variant, 9p21, was simultaneously discovered by two independent groups. 9p21 increases the risk of coronary artery disease in individuals with premature heart disease by twofold, and in the overall population the heterozygote is associated with a 25% increased risk and the homozygote with a 50% increased risk. It is of note that the risk mediated by 9p21 is independent of known risk factors. Since then, with the development of new technologies and the international consortium of CARDIoGRAM, there is now a total of 50 genetic risk variants confirmed and replicated for CAD. Of these 50, 35 mediate their risk by unknown mechanisms, indicating that the pathogenesis of atherosclerosis and myocardial infarction is due to additional factors as yet unknown. The role of genetic risk factors in the management of CAD is yet to be determined. Since many of them are independent of known risk factors, the genetic risk will in the future have to be incorporated into the guidelines, which recommend the target level of plasma LDL-C to be achieved based on the number of risk factors.

The impact of tuition fees amount on mental health over time in British students

BACKGROUND

Previous studies have shown a relationship between debt and mental health problems in students. This study aimed to examine the effect of differences in tuition fees amount on changes in mental health over time.

METHODS

A prospective cohort study followed 390 first-year British students who differed on their tuition fees level at 4 time points across their first 2 years at university. Participants completed measures of global mental health, depression, anxiety, stress, alcohol-related problems at up to four time points in their first two years at university. Mixed-factorial ANOVAs were used to assess the impact of tuition fees amount on changes in scores over time.

RESULTS

There was no difference based on fees at Time 1 for anxiety, stress, depression and global mental health. At Time 2, those charged £0-2.9k or £3-4k improved while those charged £8-9k stayed the same. However, this trend reversed by Times 3 and 4.

CONCLUSIONS

Undergraduates mental health is partially affected by the level of tuition fees; however, the recent increase in tuition fees does not appear to have had a lasting impact at present.

A genetic basis for coronary artery disease

CAD and cancer account for over one-half of all deaths in the world. It is claimed that the 21st century is the last century for CAD. This is, in part, because CAD is preventable based on randomized, placebo-controlled clinical trials, which show modifying known risk factors such as cholesterol is associated consistently with 40-60% reduction in morbidity and mortality from CAD. Comprehensive prevention will require modifying genetic risk factors that are claimed to account for 40-60% of predisposition to CAD. The 21st century is meeting this challenge with over 50 genetic risk variants discovered and replicated in large genome-wide association studies involving over 200,000 cases and controls. Similarly, 157 genetic variants have been discovered that regulate plasma lipids including, LDL-C, HDL-C, triglycerides, and total cholesterol. A major finding from these studies is that only 15 of the 50 genetic variants for CAD act through known risk factors. Hence, the pathogenesis of CAD in addition to cholesterol and other known risk factors is due to various other factors, many of which remain unknown. Secondly, genes regulating the plasma triglyceride levels are strongly associated with the pathogenesis of CAD. Thirdly, Mendelian randomization studies show no protection from genes that increase plasma HDL cholesterol. This is contrary to current opinion. These genetic risk variants have provided new targets for the development of novel therapies to prevent CAD. Already a new and potent drug has been developed targeting PCSK9, which is in phase 3 clinical trials and shows great efficacy and safety for prevention of CAD. The 21st century is looking very bright for the prevention of CAD.

Plasma PCSK9 levels are elevated with acute myocardial infarction in two independent retrospective angiographic studies

Objective

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a circulating protein that promotes degradation of the low density lipoprotein (LDL) receptor. Mutations that block PCSK9 secretion reduce LDL-cholesterol and the incidence of myocardial infarction (MI). However, it remains unclear whether elevated plasma PCSK9 associates with coronary atherosclerosis (CAD) or more directly with rupture of the plaque causing MI.

Methods and Results

Plasma PCSK9 was measured by ELISA in 645 angiographically defined controls (<30% coronary stenosis) and 3,273 cases of CAD (>50% stenosis in a major coronary artery) from the Ottawa Heart Genomics Study. Because lipid lowering medications elevated plasma PCSK9, confounding association with disease, only individuals not taking a lipid lowering medication were considered (279 controls and 492 with CAD). Replication was sought in 357 controls and 465 with CAD from the Emory Cardiology Biobank study. PCSK9 levels were not associated with CAD in Ottawa, but were elevated with CAD in Emory. Plasma PCSK9 levels were elevated in 45 cases with acute MI (363.5±140.0 ng/ml) compared to 398 CAD cases without MI (302.0±91.3 ng/ml, p = 0.004) in Ottawa. This finding was replicated in the Emory study in 74 cases of acute MI (445.0±171.7 ng/ml) compared to 273 CAD cases without MI (369.9±139.1 ng/ml, p = 3.7×10⁻⁴). Since PCSK9 levels were similar in CAD patients with or without a prior (non-acute) MI, our finding suggests that plasma PCSK9 is elevated either immediately prior to or at the time of MI.

Conclusion

Plasma PCSK9 levels are increased with acute MI.

Assessment of core and accessory genetic variation in Rhizobium leguminosarum symbiovar trifolii strains from diverse locations and host plants using PCR-based methods

The nitrogen-fixing symbiosis between Rhizobium leguminosarum and host legumes is recognized as a key part of sustainable agriculture. A culture collection containing rhizobia isolated from legumes of economic importance in the UK and worldwide, maintained at Rothamsted Research for many years, provided material for this study. We aimed to develop and validate efficient molecular diagnostics to investigate whether the host plant or geographical location had a greater influence on the genetic diversity of rhizobial isolates, and the extent to which the core bacterial genome and the accessory symbiosis genes located on plasmids were affected. To achieve this, core housekeeping genes and those involved in symbiosis interactions were sequenced and compared with genome-sequenced strains in the public domain. Results showed that some Rh. leguminosarum symbiovar trifolii strains nodulating clovers and Rh. leguminosarum sv. viciae strains nodulating peas and vicias shared identical housekeeping genes, clover nodule isolates from the same location could have divergent symbiosis genes, and others isolated on different continents could be very similar. This illustrates the likely co-migration of rhizobia and their legume hosts when crops are planted in new areas and indicates that selective pressure may arise from both local conditions and crop host genotypes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The nitrogen-fixing symbiosis between Rhizobium leguminosarum and host legumes has been recognized as a key part of sustainable agriculture for many years; this study provides new tools to study rhizobial biogeography which will be invaluable for extending the cultivation of legumes and indicating whether or not inoculation is necessary.

SPG7 variant escapes phosphorylation-regulated processing by AFG3L2, elevates mitochondrial ROS, and is associated with multiple clinical phenotypes

Mitochondrial production of reactive oxygen species (ROS) affects many processes in health and disease. SPG7 assembles with AFG3L2 into the mAAA protease at the inner membrane of mitochondria, degrades damaged proteins, and regulates the synthesis of mitochondrial ribosomes. SPG7 is cleaved and activated by AFG3L2 upon assembly. A variant in SPG7 that replaces arginine 688 with glutamine (Q688) is associated with several phenotypes, including toxicity of chemotherapeutic agents, type 2 diabetes mellitus, and (as reported here) coronary artery disease. We demonstrate that SPG7 processing is regulated by tyrosine phosphorylation of AFG3L2. Carriers of Q688 bypass this regulation and constitutively process and activate SPG7 mAAA protease. Cells expressing Q688 produce higher ATP levels and ROS, promoting cell proliferation. Our results thus reveal an unexpected link between the phosphorylation-dependent regulation of the mitochondria mAAA protease affecting ROS production and several clinical phenotypes.

Comparative genome-wide association studies in mice and humans for trimethylamine N-oxide, a proatherogenic metabolite of choline and L-carnitine

OBJECTIVE

Elevated levels of plasma trimethylamine N-oxide (TMAO), the product of gut microbiome and hepatic-mediated metabolism of dietary choline and L-carnitine, have recently been identified as a novel risk factor for the development of atherosclerosis in mice and humans. The goal of this study was to identify the genetic factors associated with plasma TMAO levels.

APPROACH AND RESULTS

We used comparative genome-wide association study approaches to discover loci for plasma TMAO levels in mice and humans. A genome-wide association study in the hybrid mouse diversity panel identified a locus for TMAO levels on chromosome 3 (P=2.37 × 10(-6)) that colocalized with a highly significant (P=1.07 × 10(-20)) cis-expression quantitative trait locus for solute carrier family 30 member 7. This zinc transporter could thus represent 1 positional candidate gene responsible for the association signal at this locus in mice. A genome-wide association study for plasma TMAO levels in 1973 humans identified 2 loci with suggestive evidence of association (P=3.0 × 10(-7)) on chromosomes 1q23.3 and 2p12. However, genotyping of the lead variants at these loci in 1892 additional subjects failed to replicate their association with plasma TMAO levels.

CONCLUSIONS

The results of these limited observational studies indicate that, at least in humans, genes play a marginal role in determining TMAO levels and that any genetic effects are relatively weak and complex. Variation in diet or the repertoire of gut microbiota may be more important determinants of plasma TMAO levels in mice and humans, which should be investigated in future studies.

Hypoglycemia-associated autonomic failure in healthy humans: comparison of two vs three periods of hypoglycemia on hypoglycemia-induced counterregulatory and symptom response 5 days later

CONTEXT

Hypoglycemia-associated autonomic failure (HAAF) limits the ability of patients with diabetes to achieve target glycemia. Animal models have provided insights into the pathogenesis of HAAF, but a robust human model of HAAF in which recurrent hypoglycemia impacts the counterregulatory responses to hypoglycemia days later is lacking.

OBJECTIVE

The aim of this study was to determine the impact of two or three episodes of moderate hypoglycemia on counterregulatory responses to subsequent hypoglycemia induced 5 days later.

DESIGN AND SUBJECTS

Six healthy subjects participated in each of the two study protocols. In both protocol 1 and 2, subjects underwent two 2-hour hypoglycemic clamp studies during the morning and afternoon of day 1. In protocol 2, subjects underwent an additional third hypoglycemic clamp during the morning of day 2. All subjects in both protocols underwent a final hypoglycemic clamp on the morning of day 5.

RESULTS

In protocol 1, there were no significant differences in the hypoglycemia-induced hormone response or in symptoms scores between the mornings of days 1 and 5. In protocol 2, hypoglycemia-induced epinephrine (P = .02) and cortisol (P = .04) secretions were significantly lower on day 5 compared with day 1, whereas glucagon (P = .08) and norepinephrine (P = .59) were not different. Also in protocol 2, neurogenic (P = .02) and neuroglycopenic (P = .04) symptoms during hypoglycemia were decreased on day 5 compared with day 1.

CONCLUSION

These results demonstrate that exposure of healthy humans to three 2-hour hypoglycemic episodes over 30 hours leads to significant blunting in counterregulatory and symptom response to subsequent hypoglycemia on day 5.