GENETICS AND PREDICTION OF CEREBRAL EDEMA AFTER HEMISPHERIC STROKE

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PROJECT SUMMARY The greatest contributor to neurological deterioration in the first week after stroke is development of brain swelling around the area of infarction. However, only half of those with large strokes develop malignant cerebral edema sufficient to compress adjacent brain structures and threaten survival. Clinical factors including stroke size do not explain the degree of edema that develops. Instead, it is likely that intrinsic differences in cellular mechanisms and biologic pathways activated after stroke contribute to the observed heterogeneity in swelling. We believe that identifying the genetic factors underlying this biologic variability will provide important actionable knowledge that could lead to improved targeted treatments for edema and better prediction of who is at risk. In order to study the biology of cerebral edema, we need to capture the full spectrum of its severity with an accurate and quantifiable measure of swelling. We have developed a novel marker of edema severity that measures amount of CSF pushed out of the brain as the stroke swells. This measure (∆CSF) has been validated in a preliminary study and we will now refine it by modeling ∆CSF at any time point (whenever CT is performed, using 400 scans already acquired coupled to an automated algorithm we have developed). This intermediate phenotype will capture rate of edema formation and be able to quantify which patients have relatively malignant trajectories vs. those who are relatively protected (given their stroke severity and infarct size) against developing edema. We are continuing to acquire CT scans from subjects enrolled in a large multi-site acute stroke study that already has almost 3,000 patients genotyped (supported by my primary mentor, Jin-Moo Lee’s R01 grant studying neurological improvement after stroke). We will measure rate of ∆CSF in this larger (and still expanding) cohort and quantify the residual variability (adjusting for clinical covariates) in order to ascertain for potential genetic component. Our genomic analyses of this edema endophenotype will include GCTA, a means of estimating total heritability, followed by genome-wide association study to identify common polymorphisms associated with our continuous measure of edema. This unbiased discovery approach will be supplemented by modern evolving means of uncovering rare variants and genetic pathways that could further explain heritability of edema and provide refined biologic targets. I will also learn to evaluate the functional significance of any potential genetic markers identified with these analyses. I will be mentored in these bioinformatics and quantitative genomic methods by Dr. Carlos Cruchaga, a geneticist with special expertise in dissecting complex traits using quantitative endophenotypes (e.g. CSF tau levels as intermediate phenotypes for Alzheimer’s disease). This project represents not only the first study of the genetic basis of cerebral edema but also a first step in a research pathway that will continue as I move toward independent funding to further understand edema, a disease with immense significance across all forms of brain injury. I plan to continue building upon my training and data by replicating and sequencing promising targets and expanding upon them by studying convergent phenotypes such as hemorrhagic transformation after stroke. I will also leverage my training to construct a clinical-genetic risk score for edema after stroke, incorporating the most informative genetic markers for malignant edema. Ultimately, the information gained on biology of edema could inform therapeutic interventions to block edema as we move towards a precision-medicine approach to managing brain injury.