Genetic contribution to functional outcome and disability after stroke

Resumen

Cerebrovascular disease is the leading cause of disability in adults. Independent of clinical variables such as infarct size and location, stroke subtype, and vascular risk factors, individuals have disparate responses during the recovery process after a stroke is diagnosed. This degree of response is known to be influenced by many factors. Different metabolic pathways are involved in the cerebral ischemic damage response and their activity may be modulated by variation in the genes encoding their components. Thus, the aim of this thesis was to identify the genetic and epigenetic components underlying the recovery process after ischemic stroke in order to in a near future improve the prognosis and reduce the disability rates by personalizing the rehabilitation strategies. Studying the genetic component of a complex disease is still a challenging task for scientists. Complex traits depend largely on the individual’s environment and lifestyle, and also on multiple genetic variants with small effects. The interplay between genetic and environmental factors is the key to understand the pathophysiology of such diseases. Ischemic stroke outcome is conditioned by the effect of multiple clinical parameters. For this reason, the first step of this project was to define and establish extremely restrictive selection criteria to obtain a highly homogeneous cohort. Patients were selected with functional independence previous to an anterior territory stroke. Exclusion criteria included patients with minor and lacunar strokes, among other constraints. Therefore, to carry out this project it was imperative to request collaboration from International Consortia in order to overcome the major limiting factor, the sample size. To elucidate the genomic contribution to ischemic stroke outcome, the present thesis used 4 different techniques based on the latest technologic advances. First, a meta-analysis of genome-wide association studies (GWAS) to detect common single nucleotide variants (SNPs) associated with functional status at 3 months post-stroke (the variants most strongly related to functional outcome were selected for replication in an independent set of individuals). Second, as a complementary technique, an exome sequencing study (WES) comparing two groups of ischemic stroke cases with poor or favorable outcome, was used to identify rare genetic variants. The third approach was an epigenome-wide association study (EWAS) to evaluate the influence of acute phase DNA methylation status on functional outcome. The fourth technique utilized a gene expression analysis with candidate regions previously identified. Measures of outcome at 3 months were rated according to modified Rankin Scale (mRS) by trained neurologists. As a result of this research, a novel locus in PATJ gene was identified as strongly associated with functional outcome after stroke. The EWAS also identified three methylation loci which were statistically significant, where the most striking occurrence was found on the TRPV1 gene. The results presented in this thesis demonstrates the first findings supported with a meta-analysis at genome-wide level of the genetic contribution to mid-term stroke prognosis, as well as the first epigenome-wide association study on ischemic stroke functional outcome.