Michael Chong

Genetic Markers of Inflammation and Their Role in Cardiovascular Disease

Atherosclerosis and associated cardiovascular diseases (CVD) are multifaceted disorders, influenced by environmental and heritable risk factors. Inflammation plays a significant role in each stage of atherosclerosis and as such, discovery and characterization of inflammatory biomarkers associated with risk of CVD is an active area of research. Because of the strong predicted genetic components of both CVD and inflammatory biomarkers, there is interest in identifying genetic determinants of inflammatory markers and characterizing their role in CVD. Recent developments in the methodological approaches of genetic epidemiology, especially genome-wide association studies and Mendelian randomization studies, have been effective in identifying novel gene associations and determining the causality of these genes with CVD. In this review, we will summarize the current understanding of the genetic architecture of inflammatory markers. The markers selected for this review include C-reactive protein, soluble intercellular adhesion molecule-1, interleukin-6, and P-selectin.

Identification of Cadherin 2 ( cdh2 ) Mutations in Arrhythmogenic Right Ventricular Cardiomyopathy

Background— Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetically heterogeneous condition caused by mutations in genes encoding desmosomal proteins in up to 60% of cases. The 40% of genotype-negative cases point to the need of identifying novel genetic substrates by studying genotype-negative ARVC families. Methods and Results— Whole exome sequencing was performed on 2 cousins with ARVC. Validation of 13 heterozygous variants that survived internal quality and frequency filters was performed by Sanger sequencing. These variants were also genotyped in all family members to establish genotype–phenotype cosegregation. High-resolution melting analysis followed by Sanger sequencing was used to screen for mutations in cadherin 2 (CDH2) gene in unrelated genotype-negative patients with ARVC. In a 3-generation family, we identified by whole exome sequencing a novel mutation in CDH2 (c.686A>C, p.Gln229Pro) that cosegregated with ARVC in affected family members. The CDH2 c.686A>C variant was not present in >200 000 chromosomes available through public databases, which changes a conserved amino acid of cadherin 2 protein and is supported as the causal mutation by parametric linkage analysis. We subsequently screened 73 genotype-negative ARVC probands tested previously for mutations in known ARVC genes and found an additional likely pathogenic variant in CDH2 (c.1219G>A, p.Asp407Asn). CDH2 encodes cadherin 2 (also known as N-cadherin), a protein that plays a vital role in cell adhesion, making it a biologically plausible candidate gene in ARVC pathogenesis. Conclusions— These data implicate CDH2 mutations as novel genetic causes of ARVC and contribute to a more complete identification of disease genes involved in cardiomyopathy.

Cerebrovascular Disease Knowledge Portal: An Open-Access Data Resource to Accelerate Genomic Discoveries in Stroke

Stroke is a leading cause of death and disability across the globe, affecting 15 million people each year.1 Stroke represents an archetypical common complex disease with both genetic and environmental determinants2,3 playing a role in its occurrence. The proportion of stroke risk that can be attributed to genetic variation has been estimated to be 30%.4–6 Although this estimate provides an indication of the overall importance of genetic variation in stroke, the key to developing new treatment strategies is to identify the specific genetic variants (mutations) that modify an individual’s risk of stroke. Genetic association studies (GWAS) seek to identify these variants and link them to specific genes, which, in turn, point to specific cellular processes to become therapeutic targets for drug development. In addition, newly discovered genetic risk loci can be used to improve existing phenotyping systems, enhance prediction tools aimed to identify high-risk patients, and aid in establishing causality for associations involving nongenetic exposures. Successfully identifying the range of genetic variants that cause stroke and leveraging these discoveries to reduce the suffering caused by this condition requires overcoming several key challenges. First, stroke is the final result of multiple different pathological processes and must, therefore, be accurately subtyped to identify underlying biology. Second, because large number of cases and controls are required to identify the culprit genetic variants, tens (even hundreds) of thousands of cases must be studied, requiring the collaboration of multiple centers, many of which use different ascertainment methods and criteria. Third, because genetic variation differs across the globe, representative populations from all ethnicities must be studied. Finally, all these data must be shared rapidly and widely to ensure the most expedited progress in research and enable investigators with the brightest ideas to utilize these data provided by patients to …

Mendelian Genes and Risk of Intracerebral Hemorrhage and Small-Vessel Ischemic Stroke in Sporadic Cases

Background and Purpose— Mendelian strokes are rare genetic disorders characterized by early-onset small-vessel stroke. Although extensively studied among families with syndromic features, whether these genes affect risk among sporadic cases is unknown. Methods— We sequenced 8 genes responsible for Mendelian stroke in a case–control study of sporadic stroke cases (⩽70 years). Participants included 1251 primary stroke cases of small-vessel pathology (637 intracerebral hemorrhage and 614 small-vessel ischemic stroke cases) and 1716 controls from the INTERSTROKE study (Study of the Importance of Conventional and Emerging Risk Factors of Stroke in Different Regions and Ethnic Groups of the World). Results— Overall, the prevalence of canonical disease-causing mutations was 0.56% in cases and 0.23% in controls (odds ratio=1.89; 95% confidence interval, 0.54–7.57; P=0.33). CADASIL (Cerebral Autosomal Dominant Arteriopathies with Subcortical Infarcts and Leukoencephalopathies) mutations were more frequent among cases (0.48%) than controls (0.23%) but were not significantly associated with stroke risk (odds ratio=2.03; 95% confidence interval, 0.58–8.02; P=0.27). Next, we included all rare nonsynonymous mutations to investigate whether other types of mutations may contribute to stroke risk. Overall, 13.5% of cases and 14.2% of controls were carriers of at least one rare nonsynonymous mutation among the 8 Mendelian stroke genes. Mutation carriers were not at elevated risk of stroke (odds ratio=0.93; 95% confidence interval, 0.75–1.16; P=0.55). Conclusions— In the absence of syndromic features and family history of stroke, screening for Mendelian mutations among small-vessel stroke patients is unlikely to have high diagnostic utility.

Molecular phenotype and bleeding risks of an inherited platelet disorder in a family with a RUNX1 frameshift mutation

Inherited defects in RUNX1 are important causes of platelet function disorders.

Polygenic Contribution in Individuals With Early-Onset Coronary Artery DiseaseClinical Perspective

Background: Despite evidence of high heritability, monogenic disorders are identified in a minor fraction of individuals with early-onset coronary artery disease (EOCAD). We hypothesized that some individuals with EOCAD carry a high number of common genetic risk variants, with a combined effect similar to Mendelian forms of coronary artery disease, such as familial hypercholesterolemia. Methods and Results: To confirm the polygenic contribution to EOCAD (age of ⩽40 years for men and ⩽45 years for women), we calculated in 111 418 British participants from the UK Biobank cohort a genetic risk score (GRS) based on the presence of 182 independent variants associated with coronary artery disease (GRS182). Participants with a diagnosis of EOCAD who underwent a revascularization procedure (n=96) had a significantly higher GRS182 (P=3.21×10−9) than those without EOCAD. An increase of 1 SD in GRS182 corresponded to an odds ratio of 1.84 (1.52–2.24) for EOCAD. The prevalence of a polygenic contribution that increased EOCAD risk similar to what is observed in heterozygous familial hypercholesterolemia was estimated at 1 in 53. In a local cohort of individuals with EOCAD (n=30), GRS182 was significantly increased compared with UK Biobank controls (P=0.001). Seven participants (23%) had a GRS182 corresponding to an estimated 2-fold increase in EOCAD risk; none had a rare mutation involved in monogenic dyslipidemia or EOCAD. Conclusions: These results suggest a significant polygenic contribution in individuals presenting with EOCAD, which could be more prevalent than familial hypercholesterolemia. Determination of the polygenic risk component could be included in the diagnostic workup of patients with EOCAD.