Cardiovascular disease-wide association study to investigate shared genetics with peak oxygen uptake

Introduction

Cardiorespiratory fitness, measured as peak oxygen uptake (VO2peak), is a strong predictor of cardiovascular disease (CVD) morbidity and mortality and is estimated to have a large genetic component (∼60%). However, the genetic determinants are yet to be established. Our research group recently identified novel genetic variants associated with directly measured VO2peak. Interestingly, most were specific to females. Looking into genetic pleiotropy between VO2peak and CVD can help elucidate the biological mechanisms explaining the link between this fitness related trait and disease, and potentially identify new therapeutic targets.

Purpose

The association study aims to investigate if genetic variants found to be associated with VO2peak in women is associated with any cardiovascular disease phenotypes.

Methods

34,188 female participants with genotype data from the Trøndelag Health Study (HUNT) were included in this study. ICD-coded hospital data related to cardiovascular disease was collected on each participant and the ICD codes were mapped to Phecodes, resulting in 100 disease-specific phenotypes. 26 single nucleotide polymorphisms (SNPs) previously found to be associated with directly measured VO2peak (p<5e-6) were included in the analyses, all common variants (minor allele frequency ≥1%). Each of the 26 genetic variants were tested for association with the 100 phenotypes using a logistic mixed model as implemented in SAIGE. The analysis was adjusted for birthyear and ten principal components of ancestry. The Benjamini-Hochberg false discovery rate (FDR) procedure controlling the FDR at 0.05 was used to correct for the number of tested SNPs and phenotypes.

Results

After testing each of the 26 SNPs for association with 100 cardiovascular disease phenotypes, 133 SNP-phenotype associations were nominally significant (p<0.05). The association between rs17066736 and myocarditis had the lowest p-value (1.7e-4). Among the other tested SNP-phenotype pairs were phenotypes related to ischemic heart disease, cardiac conduction disorders, heart failure, cerebrovascular disease, and diseases of arteries and veins. However, when adjusting for multiple testing, none reached overall statistical significance.

Conclusions

The findings showed no statistically significant associations between genetic variants associated with VO2peak and cardiovascular disease phenotypes in women. The role of inborn VO2peak in prediction of CVD (in women) needs further assessment.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): NTNU biotechnology

New genetic determinants of VO2max-level identified by GWAS: The HUNT Study

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Central Norway Regional Health Authority

Norwegian Health Association

Introduction

Cardiovascular disease (CVD) is the leading cause of death worldwide. Several studies have shown that low cardiorespiratory fitness (CRF) is a major risk factor for CVD and is suggested to be a stronger predictor of CVD morbidity and mortality than established cardiovascular risk factors.

CRF quantified as maximal oxygen uptake (VO2max) has a strong genetic component, estimated to be ~50%. Unfortunately, current studies on genetic markers for CRF are limited by small sample sizes. In addition, there are few studies on directly measured VO2max, as most of the previous studies are based on estimated CRF. To overcome these limitations, we performed a large-scale systematic screening for genetic variants associated with VO2max aiming to provide awaited insight to this complex trait and discover possible links between VO2max and CVD.

Purpose

To identify and validate genetic factors associated with VO2max.

Methods

The genotypes of 70,000 participants from the Trøndelag Health study (HUNT) were imputed providing information on 25 million single-nucleotide polymorphisms (SNPs). We conducted a genome-wide association study (GWAS) including 4,525 participants with directly measured VO2max from the HUNT3 Fitness study. The GWAS was performed using BOLT-LMM, adjusted for age, gender, physical activity, principal components, and genotyping batch. In addition, we ran a GWAS with the same covariates except physical activity. Further, gender specific analyses were conducted. For validation, similar analyses were performed in the United Kingdom Biobank (UKBB). In the UKBB, CRF was assessed through a submaximal bicycle test. The analyses of UKBB included ~60,000 participants and over 90 million SNPs. Functional analyses of the GWAS results were examined by functional mapping and annotation (FUMA).

Results

Two GWAS-significant (p < 5×10-8) SNPs associated with VO2max were identified in the total population, two in the male population, and 24 in the female population in HUNT. Two of the 24 SNPs found in the female population were nominally significant in the UKBB. One of the validated SNPs in the female population is located inside PIK3R5, that is shown to be of importance in cardiac function and CVD. In addition, the functional analyses in the total- and male population revealed candidate SNPs in a gene previously found to be associated with endurance, PPP3CA.

Conclusions

We have identified 28 novel SNPs associated with VO2max in the HUNT cohort. Two of these SNPs were nominally validated in females in UKBB. One of the validated SNPs resides within a gene previously reported to be related to heart function and CVD. In addition, the functional analyses in the total- and male population revealed candidate SNPs in a gene previously found to be associated with endurance. Further functional analyses using bioinformatic approaches may provide more information on the physiological importance of these findings and their relation to CVD.

Identifying new genetic markers for maximal oxygen uptake

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Central Norway Regional Health AuthorityNorwegian Health Association

Introduction

Cardiovascular disease (CVD) is the leading cause of death worldwide. Several studies have shown that low cardiorespiratory fitness (CRF) is a major risk factor for CVD. Low CRF is suggested to be a stronger predictor of CVD morbidity and mortality than established cardiovascular risk factors like obesity, diabetes, and cholesterol.

Several studies suggest that CRF quantified as maximal oxygen uptake (VO2max) has a strong genetic component, estimated to be ~50%. Unfortunately, current studies on genetic markers for CRF are limited by small sample sizes. In addition, there are few studies on directly measured VO2max, as most of the previous studies are based on estimated CRF. Directly measured VO2max is considered as the gold standard for measuring CRF. Thus, a large-scale systematic screening for genetic variants associated with VO2max may provide awaited insight to this complex trait and discover possible links between VO2max and CVD.

Purpose

To identify and validate genetic factors associated with VO2max.

Methods

The genotypes of 70.000 participants from the Trøndelag Health study (HUNT) were imputed providing information on 25 million SNPs. We conducted a genome-wide association study (GWAS) including 4525 participants with directly measured VO2max from the HUNT3 Fitness study. The GWAS was performed using BOLT-LMM, adjusted for age, gender, physical activity, principal components, and genotyping batch. In addition, we ran a GWAS with the same covariates except physical activity. Further, gender specific analyses were conducted. For validation, similar analyses were performed in the United Kingdom Biobank (UKBB). In the UKBB, CRF was assessed through a submaximal bicycle test. The analyses of UKBB included ~60.000 participants and over 90 million SNPs.

Results

Two GWAS-significant (p < 5x10-8) SNPs associated with VO2max were identified in the total population in HUNT. Further, 24 GWAS-significant SNPs associated with VO2max in females, and two GWAS-significant SNPs associated with VO2max in males were discovered. Two of the 24 SNPs found in the female population were nominally significant in the UKBB. The validated SNPs are rs376927175, an intergenic SNP downstream of APBA1, and rs551942830 (proxy for rs190675254 with LD = 1.0), a 3 Prime UTR variant inside PIK3R5. PIK3R5 encodes the regulatory subunit of one class of PI3Ks, that is shown to be of importance in cardiac function and CVD. None of the SNPs found in the total population nor the male population were validated in UKBB.

Conclusions

We have identified 28 novel SNPs associated with VO2max in the HUNT cohort. Two of these SNPs were nominally validated in females in UKBB. One of the validated SNPs resides within a gene previously reported to be related to heart function and CVD. Further functional analyses using bioinformatic approaches may provide more information on the physiological importance of these findings and their relation to CVD.

Lipoprotein subfraction LDL-5 and the presence of coronary atherosclerosis

Background

Coronary artery disease (CAD) has high mortality rates and is a frequent cause of death globally. Serum lipids play a pivotal role in the development of atherosclerosis, and elevated levels of total cholesterol, low density lipoprotein (LDL) cholesterol, and triglycerides are well known risk factors of cardiovascular disease (CVD). However, there are limitations in the ability to predict CVD risk, which has led to an increased clinical interest in identifying novel risk markers. With the advances in lipidomic technology, lipoprotein subfractions may provide additional information that is missing in today's evaluation of CVD risk. Lipoprotein subfractions differ in size and density, and recent studies suggest that high density of small LDL particles provide a greater risk for CVD.

Purpose

To investigate whether lipoprotein subfractions are associated with the presence and extent of coronary atherosclerosis.

Methods

Fasting serum samples from 60 participants with suspected stable CAD were collected before scheduled coronary angiography, and analysed by nuclear magnetic resonance (NMR). The presence and extent of atherosclerosis were quantified by the Gensini Score. Participants were classified into one of three Gensini groups based on severity (<20.5, normal; 20.6–30, non-significant CAD; >30.1, significant CAD).

Results

A three-way ANOVA, adjusted for statin-use and sex, revealed statistically significant differences (p<0.005) in LDL-5 particle number, LDL-5 triglycerides, and LDL-5 phospholipids between the Gensini groups. In addition, significant differences (p<0.005) were found in the ratios apolipoprotein A/apolipoprotein B and LDL cholesterol/HDL cholesterol between the Gensini groups. All significant variables, identified by the three-way ANOVA, displayed the highest levels in the Gensini group with significant CAD.

Conclusion

Despite no difference in the traditional clinical measurements (total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides), NMR-lipidomics revealed significant differences in LDL-5 between the Gensini groups. Interestingly, our results reveal that those with significant CAD have a higher density of small LDL subfractions.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): Norwegian Health Association, The Liaison Committee for Education, Research and Innovation in Central Norway