Jessica Dennis
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The last decade has seen an unprecedented explosion of data. In medicine, data are increasingly being generated and linked across electronic health records, administrative databases, and biobanked samples. These resources hold tremendous promise for improving human health and achieving precision medicine, which will only be realized by thoughtful study designs and innovative analyses.
My lab studies life course genetic epidemiology. We aim to understand how our genes, which are fixed at conception, interact with changing environments across time, and ultimately, affect traits and conditions that manifest throughout the lifecourse. Our overall goal is to improve precision health by matching the right preventative strategy or treatment, to the right person, at the right time. To achieve this, we apply computational methods to large-scale genomic and population health datasets that include longitudinal measures of health and disease, collected at different life stages. Brain related traits are a major area of focus, because change over time is a hallmark of psychiatric and neurodegenerative conditions.
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Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
The majority of genetic loci that influence complex traits are non-coding. Roughly half of these loci affect gene expression in one or more tissues, despite making up less than 10% of common genetic variants. However, it is increasingly unlikely that genetic effects on gene expression will be sufficient to assign a function to all non-coding risk loci. This thesis splits the problem of assigning new functions to complex trait loci into two steps.First, I aim to increase the number of non-coding loci with a known function without requiring new molecular datasets. In my thesis, I explore context-dependent genetic regulation of molecular traits, where the context that affects this process is either inferred from data or a common phenotypic measure like sex. I then advocate for associating genetic variation with molecular data other than gene expression, primarily on DNA methylation.Second, I outline how to tie these novel molecular functions to genetic risk for complex traits. Importantly, this requires methods and workflows that summarize genetic effects at individual loci across interpretable functional units (genes) and genome-wide genetic risk for complex traits.In my scholarship chapters, I first show that environments inferred from global gene expression can correlate with various phenotypic and environmental variables. These inferred contexts are replicated across samples and can subsequently be used to identify novel context-specific genetic regulation of gene expression. I then show that novel context-specific genetic regulation can be approached in DNA methylation using sex, measured in virtually all genetic and molecular datasets.My later chapters demonstrate how to summarize genetic effects to learn which traits are particularly relevant to these novel regulatory relationships. I start with effects and individual loci and then explore methods to interpret the gene-level influence of genetic effects on DNA methylation. Then I demonstrate how cumulative, genome-wide risk for complex traits can provide new insight into the biological functions underlying complex traits beyond the effects I observe at individual loci.Overall this thesis shows that we require various approaches to discover disease-relevant molecular functions of non-coding genetic loci.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Major depressive disorder (MDD) is a leading cause of morbidity and disability worldwide, with approximately twice as many women reported to have a lifetime occurrence of MDD than men. MDD is a polygenic trait, wherein hundreds to thousands of common genetic variants with small effect sizes contribute to risk of disease. This study investigated sex differences in the risk factor comorbidity and genetic architecture of MDD in over 16,000 people aged 45-85 from the Canadian Longitudinal Study on Aging (CLSA), with 21% of females (n=1,741) and 12% of males (n=1,055) coded with MDD. Polygenic risk scores (PRS) for individuals were made using sex-stratified and non-sex-specific (“both-sexes”) UK Biobank genome-wide association study summary statistics data. The female sex-specific PRS had higher associations with MDD in females in the top decile of PRS risk (OR = 1.68 (1.32-2.14), p = 2.8E-05) than the male-specific PRS in males (OR = 1.43 (1.07-1.93), p = 0.017) and the both-sexes PRS applied to both sexes (OR = 1.51 (1.25-1.83), p = 2.5E-05). Odds of MDD for the sex-specific PRSs, socioeconomic, lifestyle and clinical risk factors were assessed using a multivariable logistic regression model for each sex. Sex-specific risk factor associations with odds of MDD were found in females (hypothyroidism (OR = 1.42 (1.25-1.63), p = 1.74E-07), not being partnered (OR = 1.34 (1.17-1.52), p = 1.26E-05), having diabetes (OR = 1.30 (1.11-1.52), p = 1.03E-03), higher sex-specific autosomal PRS (OR = 1.10 (1.04-1.16), p = 6.15E-04) and a history of ischemic heart disease (OR = 1.52 (1.14-2.01), p = 3.39E-03)) and males (high blood pressure, OR = 1.35 (1.04-1.47), p = 4.55E-05). Significant differences were observed in the proportion of variables that contributed to the most to each model, evaluated by relative pseudo-R2 values. Age contributed the most to the model for both sexes (73% for females, 57% for males), wherein younger age was associated with higher odds of MDD. The results of this thesis underscore the relevance for sex-disaggregating analyses of complex traits, like MDD, and the incorporation of clinical variables into models of MDD, in applications such as early detection and primary prevention.
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Publications
- Association of Preinjury Medical Diagnoses with Pediatric Persistent Postconcussion Symptoms in Electronic Health Records (2022)
Journal of Head Trauma Rehabilitation, 37 (2), E80-E89 - Clinical laboratory test-wide association scan of polygenic scores identifies biomarkers of complex disease. (2021)
Genome medicine, - Genetic risk for major depressive disorder and loneliness in sex-specific associations with coronary artery disease (2021)
Molecular Psychiatry, 26 (8), 4254-4264 - A phenome-wide association study identifying risk factors for pediatric post-concussion syndrome (2020)
medRxiv, - Lab-wide association scan of polygenic scores identifies biomarkers of complex disease (2020)
medRxiv, - A/T/N polygenic risk score for cognitive decline in old age (2019)
bioRxiv, - Diagnostic Algorithms to Study Post-Concussion Syndrome Using Electronic Health Records: Validating a Method to Capture an Important Patient Population. (2019)
Journal of neurotrauma, - Penetrance and pleiotropy of polygenic risk scores for schizophrenia in 106,160 patients across four health care systems (2019)
American Journal of Psychiatry, 176 (10), 846-855 - Phenome-wide investigation of health outcomes associated with genetic predisposition to loneliness (2019)
Human Molecular Genetics, 28 (22), 3853-3865 - Penetrance and pleiotropy of polygenic risk scores for schizophrenia in 106,160 patients across four healthcare systems (2018)
- Phenome-wide Investigation of Health Outcomes Associated with Genetic Predisposition to Loneliness (2018)
- Beyond the market? New agrarianism and cooperative farmland access in North America (2017)
Journal of Rural Studies, 53, 303--316 - Blood triglyceride levels are associated with DNA methylation at the serine metabolism gene PHGDH. (2017)
Scientific reports, - Blood triglyceride levels are associated with DNA methylation at the serine metabolism gene PHGDH. (2017)
Scientific reports, - Genetic determinants of tissue factor pathway inhibitor plasma levels (2017)
Thrombosis and Haemostasis, 114 (08), 245--257 - Leveraging cell type specific regulatory regions to detect SNPs associated with tissue factor pathway inhibitor plasma levels. (2017)
Genetic epidemiology, - Leveraging cell type specific regulatory regions to detect SNPs associated with tissue factor pathway inhibitor plasma levels. (2017)
Genetic epidemiology, - Bicycling crashes on streetcar (tram) or train tracks: mixed methods to identify prevention measures. (2016)
BMC public health, - Bicycling crashes on streetcar (tram) or train tracks: mixed methods to identify prevention measures. (2016)
BMC public health, - Single nucleotide polymorphisms in an intergenic chromosome 2q region associated with tissue factor pathway inhibitor plasma levels and venous thromboembolism (2016)
Journal of Thrombosis and Haemostasis, 14 (10), 1960--1970 - Single nucleotide polymorphisms in an intergenic chromosome 2q region associated with tissue factor pathway inhibitor plasma levels and venous thromboembolism. (2016)
Journal of thrombosis and haemostasis : JTH, - Bicycling injury hospitalisation rates in Canadian jurisdictions: analyses examining associations with helmet legislation and mode share. (2015)
BMJ open, - Genome-wide investigation of DNA methylation marks associated with FV Leiden mutation. (2014)
PloS one, - RFC1 80G>A is a genetic determinant of methotrexate efficacy in rheumatoid arthritis: a human genome epidemiologic review and meta-analysis of observational studies. (2014)
Arthritis & rheumatology (Hoboken, N.J.), - Thrombin generation potential and whole-blood DNA methylation. (2014)
Thrombosis research, - Challenges of population-based colorectal cancer screening and the importance of time-trend analysis when evaluating system change. (2013)
Cancer epidemiology, - Helmet legislation and admissions to hospital for cycling related head injuries in Canadian provinces and territories: interrupted time series analysis. (2013)
The BMJ, - The endothelial protein C receptor (PROCR) Ser219Gly variant and risk of common thrombotic disorders: a HuGE review and meta-analysis of evidence from observational studies. (2012)
Blood, - Bias in the case-only design applied to studies of gene-environment and gene-gene interaction: a systematic review and meta-analysis. (2011)
International journal of epidemiology, - Breast cancer risk in relation to alcohol consumption and BRCA gene mutations--a case-only study of gene-environment interaction. (2011)
The breast journal, - Alcohol consumption and the risk of breast cancer among BRCA1 and BRCA2 mutation carriers. (2010)
Breast (Edinburgh, Scotland), - The effects of provincial bicycle helmet legislation on helmet use and bicycle ridership in Canada. (2010)
Injury prevention : journal of the International Society for Child and Adolescent Injury Prevention,
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