APOE influences vasospasm and cognition of noncomatose patients with subarachnoid hemorrhage

Apolipoprotein E Polymorphism Impacts White Matter Injury Through Microglial Phagocytosis After Experimental Subarachnoid Hemorrhage

Apolipoprotein E (apoE, protein; APOE, gene), divided into three alleles of E2, E3 and E4 in humans, is associated with the progression of white matter lesion load. However, mechanism evidence has not been reported regarding the APOE genotype in early white matter injury (WMI) under subarachnoid hemorrhage (SAH) conditions. In the present study, we investigated the effects of APOE gene polymorphisms, by constructing microglial APOE3 and APOE4-specific overexpression, on WMI and underlying mechanisms of microglia phagocytosis in a mice model of SAH. A total of 167 male C57BL/6J mice (weight 22-26 g) were used. SAH and bleeding environment were induced by endovascular perforation in vivo and oxyHb in vitro, respectively. Multi-technology approaches, including immunohistochemistry, high throughput sequencing, gene editing for adeno-associated viruses, and several molecular biotechnologies were used to validate the effects of APOE polymorphisms on microglial phagocytosis and WMI after SAH. Our results revealed that APOE4 significantly aggravated the WMI and decreased neurobehavioral function by impairing microglial phagocytosis after SAH. Indicators negatively associated with microglial phagocytosis increased like CD16, CD86 and the ratio of CD16/CD206, while the indicators positively associated with microglial phagocytosis decreased like Arg-1 and CD206. The increased ROS and aggravating mitochondrial damage demonstrated that the damaging effects of APOE4 in SAH may be associated with microglial oxidative stress-dependent mitochondrial damage. Inhibiting mitochondrial oxidative stress by Mitoquinone (mitoQ) can enhance the phagocytic function of microglia. In conclusion, anti-oxidative stress and phagocytosis protection may serve as promising treatments in the management of SAH.

Association between Apolipoprotein E Polymorphism and Clinical Outcome after Ischemic Stroke, Intracerebral Hemorrhage, and Subarachnoid Hemorrhage

BACKGROUNDS

Previous studies reported inconsistent results regarding associations between apolipoprotein E (APOE) polymorphism and clinical outcomes after ischemic stroke (IS), intracerebral hemorrhage (ICH), or subarachnoid hemorrhage (SAH). Thus, the study was designed to make a systematic review and meta-analysis regarding the association between APOE polymorphism and clinical outcome after IS, ICH, and SAH.

METHODS

To identify studies eligible for this meta-analysis, we searched for articles published before August 2021 in the databases (PubMed, Web of Science, and Google Scholar). We used STATA 12.0 software to compute hazard ratios (HRs) and their 95% confidence intervals (CIs) regarding APOE polymorphism and clinical outcome after IS, ICH, and SAH.

RESULTS

Meta-analysis showed no significant association between APOE polymorphism and functional outcome after IS with fixed effects models (ε4 carrier vs. non-ε4 carrier: HR, 1.00; 95% CI: 0.83-1.21, I2 = 29.4%, p = 0.183; ε2 carrier vs. non-ε2 carrier: HR, 0.92; 95% CI: 0.72-1.16, I2 = 15.6%, p = 0.307). Meta-analysis showed that ICH patients carrying ε4 allele have increased risk of poor outcome in Caucasian population with fixed effects models (ε4 carrier vs. non-ε4 carrier: HR, 1.75; 95% CI: 1.19-2.57, I2 = 0.0%, p = 0.543). Meta-analysis showed no significant association between APOE polymorphism and functional outcomes after SAH with random effects models (ε4 carrier vs. non-ε4 carrier: HR, 1.51; 95% CI: 0.80-2.84, I2 = 57.1%, p = 0.022).

CONCLUSIONS

In conclusion, the present study demonstrated APOE ε4 carriers show worse functional outcomes after ICH, but not after IS or SAH. More large-scale studies were critical to explore the association between APOE polymorphism and clinical outcome after IS, ICH, and SAH.

Biospecimens and Molecular and Cellular Biomarkers in Aneurysmal Subarachnoid Hemorrhage Studies: Common Data Elements and Standard Reporting Recommendations

INTRODUCTION

Development of clinical biomarkers to guide therapy is an important unmet need in aneurysmal subarachnoid hemorrhage (SAH). A wide spectrum of plausible biomarkers has been reported for SAH, but none have been validated due to significant variabilities in study design, methodology, laboratory techniques, and outcome endpoints.

METHODS

A systematic review of SAH biomarkers was performed per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The panel's recommendations focused on harmonization of (1) target cellular and molecular biomarkers for future investigation in SAH, (2) standardization of best-practice procedures in biospecimen and biomarker studies, and (3) experimental method reporting requirements to facilitate meta-analyses and future validation of putative biomarkers.

RESULTS

No cellular or molecular biomarker has been validated for inclusion as "core" recommendation. Fifty-four studies met inclusion criteria and generated 33 supplemental and emerging biomarker targets. Core recommendations include best-practice protocols for biospecimen collection and handling as well as standardized reporting guidelines to capture the heterogeneity and variabilities in experimental methodologies and biomarker analyses platforms.

CONCLUSION

Significant variabilities in study design, methodology, laboratory techniques, and outcome endpoints exist in SAH biomarker studies and present significant barriers toward validation and translation of putative biomarkers to clinical use. Adaptation of common data elements, recommended biospecimen protocols, and reporting guidelines will reduce heterogeneity and facilitate future meta-analyses and development of validated clinical biomarkers in SAH.

The Effect of the Relationship of APOE Polymorphisms and Cerebral Vasospasm on Functional Outcomes in Children With Traumatic Brain Injury

BACKGROUND

Pediatric traumatic brain injury (TBI) is a leading cause of death and disability. Polymorphisms in the apolipoprotein E ( APOE) gene have been linked to cerebral vasospasm (CV) and poor outcomes in adults with TBI, yet these associations remain poorly defined in children.

OBJECTIVE

We examined the effect of the relationship between APOE polymorphisms and CV on functional outcomes in children with a TBI.

METHOD

This prospective, descriptive study examined 60 children (aged 10 days to 15 years) with a TBI. Data included demographic information, genetic sampling for the APOE gene and single-nucleotide polymorphisms (SNPs; rs405509, rs429358, rs7412), and daily transcranial Doppler ultrasounds to evaluate for CV. We examined Glasgow Outcome Scale-Extended Pediatrics (GOS-E Peds) scores at the time of discharge and 4-6 weeks after discharge.

RESULTS

More than half (56.7%) of the 60 children ( M_age = 5.9 years) were male. Twenty-six participants (43.3%) experienced an occurrence of CV. There were significant differences in injury mechanism (unadjusted p = .048) and age (unadjusted p = .02) between those with and without CV. Also, the noncoding promoter SNP rs405509 T/T, when considered with injury severity, appeared to modify the relationship of APOE genotype to CV. The relationship between APOE and CV had no significant effect on GOS-E Peds scores.

CONCLUSION

Injury severity and the APOE noncoding promoter SNP rs405509 may modify the relationship between APOE and CV in children with TBI. More studies are needed to understand the role of APOE polymorphisms in outcomes in children with TBI.

Genetics and Genomics of Acute Neurologic Disorders

Neurologic diseases and injuries are complex and multifactorial, making risk prediction, targeted treatment modalities, and outcome prognostication difficult and elusive. Genetics and genomics have affected clinical practice in many aspects in medicine, particularly cancer treatment. Advancements in knowledge of genetic and genomic variability in neurologic disease and injury are growing rapidly. Although these data are not yet ready for use in clinical practice, research continues to progress and elucidate information that eventually will provide answers to complex neurologic questions and serve as a platform to provide individualized care plans aimed at improving outcomes. This article provides a focused review of relevant literature on genetics, genomics, and common complex neurologic disease and injury likely to be seen in the acute care setting.

Present Status and Future Challenges of New Therapeutic Targets in Preclinical Models of Stroke in Aged Animals with/without Comorbidities

The aging process, comorbidities, and age-associated diseases are closely dependent on each other. Cerebral ischemia impacts a wide range of systems in an age-dependent manner. However, the aging process has many facets which are influenced by the genetic background and epigenetic or environmental factors, which can explain why some people age differently than others. Therefore, there is an urgent need to identify age-related changes in body functions or structures that increase the risk for stroke and which are associated with a poor outcome. Multimodal imaging, electrophysiology, cell biology, proteomics, and transcriptomics, offer a useful approach to link structural and functional changes in the aging brain, with or without comorbidities, to post-stroke rehabilitation. This can help us to improve our knowledge about senescence firstly, and in this context, aids in elucidating the pathophysiology of age-related diseases that allows us to develop therapeutic strategies or prevent diseases. These processes, including potential therapeutical interventions, need to be studied first in relevant preclinical models using aged animals, with and without comorbidities. Therefore, preclinical research on ischemic stroke should consider age as the most important risk factor for cerebral ischemia. Furthermore, the identification of effective therapeutic strategies, corroborated with successful translational studies, will have a dramatic impact on the lives of millions of people with cerebrovascular diseases.

Apolipoprotein E polymorphism and the risk of aneurysmal subarachnoid hemorrhage in a South Indian population

Background

The rupture of a brain aneurysm causes bleeding in the subarachnoid space. This is known as aneurysmal subarachnoid hemorrhage (aSAH). We evaluated the association of apolipoprotein E (APOE) polymorphism and the risk of aSAH in a South Indian population.

Methods

The study was performed on 200 subjects with aSAH and 253 healthy control subjects. Blood samples (5 ml) were used to isolate DNA and genotyping was performed for rs7412 and rs429358 using a Taqman allelic discrimination assay. Statistical software R.3.0.11 was used to statistically analyze the data and a p value < 0.05 was considered as statistically significant.

Results

We found a significant association with the risk of aSAH in ε3/ ε4 genetic model (OR = 1.91, 95% CI = 1.16-3.14, p = 0.01). However, in the other genetic models and allele frequency, there was no significant association with the risk of aSAH. In subtyping, we found a significant association of ε2 allele frequency with posterior communicating artery (PCOM) aneurysm (OR = 3.59, 95% CI = 1.11-11.64, p = 0.03).

Conclusion

Our results suggest that APOE polymorphism has an influence on the risk of aSAH in this South Indian population, specifically in the PCOM subtype.

Minimal Long-Term Neurobehavioral Impairments after Endovascular Perforation Subarachnoid Hemorrhage in Mice

Cognitive deficits are among the most severe and pervasive consequences of aneurysmal subarachnoid hemorrhage (SAH). A critical step in developing therapies targeting such outcomes is the characterization of experimentally-tractable pre-clinical models that exhibit multi-domain neurobehavioral deficits similar to those afflicting humans. We therefore searched for neurobehavioral abnormalities following endovascular perforation induction of SAH in mice, a heavily-utilized model. We instituted a functional screen to manage variability in injury severity, then assessed acute functional deficits, as well as activity, anxiety-related behavior, learning and memory, socialization, and depressive-like behavior at sub-acute and chronic time points (up to 1 month post-injury). Animals in which SAH was induced exhibited reduced acute functional capacity and reduced general activity to 1 month post-injury. Tests of anxiety-related behavior including central area time in the elevated plus maze and thigmotaxis in the open field test revealed increased anxiety-like behavior at subacute and chronic time-points, respectively. Effect sizes for subacute and chronic neurobehavioral endpoints in other domains, however, were small. In combination with persistent variability, this led to non-significant effects of injury on all remaining neurobehavioral outcomes. These results suggest that, with the exception of anxiety-related behavior, alternate mouse models are required to effectively analyze cognitive outcomes after SAH.

Apolipoprotein E ε4: A Possible Risk Factor of Intracranial Pressure and White Matter Perfusion in Good-Grade Aneurysmal Subarachnoid Hemorrhage Patients at Early Stage

Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating and complicated disease with significant morbidity and mortality. Previous studies have shown that genetic susceptibility may play an important role in the outcome of a given individual with aSAH. This study evaluates the potential association in effects of the APOE allele on the early brain injury (EBI) in light of elevated intracranial pressure (ICP) and cerebral perfusion disorders in a consecutive series of non-comatose Chinese patients with aSAH. A total of 122 patients with aSAH (54 males and 68 females) were enrolled in this study. Demographic and clinical data were collected. We measured ICP before microsurgical clipping or endovascular coiling during the first 72 h after aneurysm rupture. Computed tomography perfusion (CTP) examination in patients was performed before treatment. The distributions of APOE genotypes and alleles matched Hardy–Weinberg law (p > 0.05). In this study, 68 patients (55.7%) had a normal ICP, whereas 54 (44.3%) had an elevated ICP. Fourteen of 21 patients with APOE ε4 had an elevated ICP, which was significantly different from those without APOE ε4 (p = 0.03). The patients with the ε4 allele had a higher incidence of elevated ICP [p = 0.009, 95% confidence interval (CI) = 1.481–15.432, odds ratio = 4.780] than those without this allele. For CTP measurements, a lower mean cerebral blood flow (difference, −4.74; 95% CI, 0.53–8.94 s, p = 0.03), longer mean transit time (difference, 0.47; 95% CI, −0.87 to −0.78, p = 0.02), and time-to-peak (difference, 2.29; 95% CI, −3.64 to −0.93 s, p = 0.02) were observed in patients with ε4 allele than in those without in the internal capsule regions. In conclusion, the APOE ε4 allele predisposes patients to elevated ICP and perfusion disorders in white matter regions during the first 72 h after aSAH. The presence of an APOE ε4 allele plays an important role in the EBI response to aSAH.

Multiple beneficial effects of melanocortin MC4 receptor agonists in experimental neurodegenerative disorders: Therapeutic perspectives

Melanocortin peptides induce neuroprotection in acute and chronic experimental neurodegenerative conditions. Melanocortins likewise counteract systemic responses to brain injuries. Furthermore, they promote neurogenesis by activating critical signaling pathways. Melanocortin-induced long-lasting improvement in synaptic activity and neurological performance, including learning and memory, sensory-motor orientation and coordinated limb use, has been consistently observed in experimental models of acute and chronic neurodegeneration. Evidence indicates that the neuroprotective and neurogenic effects of melanocortins, as well as the protection against systemic responses to a brain injury, are mediated by brain melanocortin 4 (MC₄) receptors, through an involvement of the vagus nerve. Here we discuss the targets and mechanisms underlying the multiple beneficial effects recently observed in animal models of neurodegeneration. We comment on the potential clinical usefulness of melanocortin MC₄ receptor agonists as neuroprotective and neuroregenerative agents in ischemic stroke, subarachnoid hemorrhage, traumatic brain injury, spinal cord injury, and Alzheimer's disease.

Polymorphisms of apolipoprotein E and aneurysmal subarachnoid haemorrhage: A meta-analysis

Subarachnoid haemorrhage (SAH) is characterised by bleeding in the subarachnoid space in the brain. There are various polymorphisms in genes which are associated with this disease. We performed a systematic meta- analysis to investigate the relationship of APOE polymorphism on aSAH. A comprehensive literature search was done in the Pubmed database, Science Direct, Cochrane library and Google Scholar. The OR and 95% CI were evaluated for the gene and aSAH association using fixed and random effect models. Publication bias was assessed using Begg's funnel plot and Egger's regression test. All statistical evaluations were done using the software Review Manager 5.0 and Comprehensive Meta Analysis v2.2.023. A total of 9 studies were assessed on APOE polymorphism (1100 Cases, 2732 Control). Meta analysis results showed significant association in ε2/ ε2 versus ε3/ε3, ε2 versus ε3 genetic models and ε2 allele frequency. In subgroup analysis statistically significant association was observed in Asians in the genetic models ε2/ ε2 versus ε3/ε3, ε2/ε3 versus ε3/ε3, ε2 versus ε3 and also in ε2 allele frequency. However, in Caucasian population only ε2/ε2 versus ε3/ε3 genetic model showed significant association between APOE and risk of aSAH. In this meta-analysis study, the ε2/ε2 genotype is associated with increased risk of aSAH.

Apolipoprotein E polymorphism in aneurysmal subarachnoid haemorrhage in West Sweden

BACKGROUND AND PURPOSE

Aneurysmal subarachnoid haemorrhage (aSAH) is associated with high morbidity and mortality despite novel treatments. Genetic variability may explain outcome differences. Apolipoprotein E (ApoE) is a glycoprotein with a major role in brain lipoprotein metabolism. It has three isoforms encoded by distinct alleles: APOEε2, APOEε3 and APOEε4. The APOEε4 allele is associated with Alzheimer's disease and worse outcome after traumatic brain injury and ischaemic stroke. This prospective blinded study explored the influence of the APOEε4 polymorphism on the risk of aSAH, risk of cerebral vasospasm (CVS) and 1-year neurological outcome.

METHODS

The APOΕε4 polymorphism was analysed in 147 patients with aSAH. Allele and genotype frequencies were compared to those found in a gender- and area-matched control group of healthy individuals (n = 211). Early CVS was identified and treated according to neurointensive care unit (NICU) guidelines. Neurological deficit(s) at admittance and at 1-year follow-up visit was recorded. Neurological outcome was assessed by the National Institute of Health Stroke Scale, Barthel Index and the Extended Glasgow Outcome Scale.

RESULTS

APOEε4 and non-APOEε4 allele frequencies were similar in aSAH patients and healthy individuals. The presence of APOEε4 was not associated with the development of early CVS. We could not find an influence of the APOE polymorphism on 1-year neurological outcome between groups. Subgroup analyses of patients treated with surgical clipping vs endovascular coiling did not reveal any associations.

CONCLUSIONS

The APOEε4 polymorphism has no major influence on risk of aSAH, the occurrence of CVS or long-term neurological outcome after aSAH.

Monitoring biomarkers of cellular injury and death in acute brain injury

BACKGROUND

Molecular biomarkers have revolutionalized diagnosis and treatment of many diseases, such as troponin use in myocardial infarction. Urgent need for high-fidelity biomarkers in neurocritical care has resulted in numerous studies reporting potential candidate biomarkers.

METHODS

We performed an electronic literature search and systematic review of English language articles on cellular/molecular biomarkers associated with outcome and with disease-specific secondary complications in adult patients with acute ischemic stroke (AIS), intracerebral hemorrhage (ICH), subarachnoid hemorrhage (SAH), traumatic brain injury (TBI), and post-cardiac arrest hypoxic ischemic encephalopathic injuries (HIE).

RESULTS

A total of 135 articles were included. Though a wide variety of potential biomarkers have been identified, only neuron-specific enolase has been validated in large cohorts and shows 100% specificity for poor outcome prediction in HIE patients not treated with therapeutic hypothermia. There are many promising candidate blood and CSF biomarkers in SAH, AIS, ICH, and TBI, but none yet meets criteria for routine clinical use.

CONCLUSION

Current studies vary significantly in patient selection, biosample collection/processing, and biomarker measurement protocols, thereby limiting the generalizability of overall results. Future large prospective studies with standardized treatment, biosample collection, and biomarker measurement and validation protocols are necessary to identify high-fidelity biomarkers in neurocritical care.

Role of apolipoprotein E polymorphism as a prognostic marker in traumatic brain injury and neurodegenerative disease: a critical review

OBJECT

The difference in course and outcome of several neurodegenerative conditions and traumatic injuries of the nervous system points toward a possible role of genetic and environmental factors as prognostic markers. Apolipoprotein E (Apo-E), a key player in lipid metabolism, is recognized as one of the most powerful genetic risk factors for dementia and other neurodegenerative diseases. In this article, the current understanding of APOE polymorphism in various neurological disorders is discussed.

METHODS

The English literature was searched for various studies describing the role of APOE polymorphism as a prognostic marker in neurodegenerative diseases and traumatic brain injury. The wide ethnic distribution of APOE polymorphism was discussed, and the recent meta-analyses of role of APOE polymorphism in multiple diseases were analyzed and summarized in tabular form.

RESULTS

Results from the review of literature revealed that the distribution of APOE is varied in different ethnic populations. APOE polymorphism plays a significant role in pathogenesis of neurodegeneration, particularly in Alzheimer’s disease. APOE ε4 is considered a marker for poor prognosis in various diseases, but APOE ε2 rather than APOE ε4 has been associated with cerebral amyloid angiopathy-related bleeding and sporadic Parkinson’s disease. The role of APOE polymorphism in various neurological diseases has not been conclusively elucidated.

CONCLUSIONS

Apo-E is a biomarker for various neurological and systemic diseases. Therefore, while analyzing the role of APOE polymorphism in neurological diseases, the interpretation should be done after adjusting all the confounding factors. A continuous quest to look for associations with various neurological diseases and wide knowledge of available literature are required to improve the understanding of the role of APOE polymorphism in these conditions and identify potential therapeutic targets.

Role of Genetic Polymorphisms in Predicting Delayed Cerebral Ischemia and Radiographic Vasospasm After Aneurysmal Subarachnoid Hemorrhage: A Meta-Analysis

OBJECTIVE

The pathophysiology on cerebral vasospasm and delayed cerebral ischemia (DCI) remains poorly understood. Much research has been dedicated to finding genetic loci associated with vasospasm and ischemia. We present a systematic review and meta-analysis to identify genetic polymorphisms associated with delayed ischemic neurologic deficit (DIND), radiographic infarction attributed to ischemia, and radiographic vasospasm.

METHODS

PubMed, the Cochrane Library, and Excerpta Medica dataBASE (EMBASE) databases were used to identify relevant studies published up to March 2015 containing the subject terms cerebral or intracranial vasospasm and DCI in combination with genetics, gene, polymorphism or marker. Meta-analyses were performed using a random-effects model to calculate summary odds ratio (ORs) and 95% confidence intervals for each respective gene.

RESULTS

Of 269 articles initially identified, 20 studies with 1670 patients were included in our comprehensive review, including 27 polymorphisms in 11 genes. The following 6 polymorphisms in 3 genes were selected for subsequent meta-analyses: apolipoprotein E (ApoE2, E4); endothelial nitric oxide (eNOS T786C, VNTR intron 4 a/b, G894T); and haptoglobin (Hp) 1/2 phenotypes. The eNOS VNTR a allele was associated with DIND (a vs. b allele: OR 1.92 [1.31-2.81], padj = 0.008). The Hp 2-2 allele was associated with radiographic vasospasm (2-2 vs. 2-1 and 1-1: OR 3.86 [1.86-8.03], padj = 0.003) but did not reach significance for DIND.

CONCLUSIONS

This is the first systemic review and meta-analysis to study and evaluate the associations between genetic polymorphism with DCI and radiographic vasospasm independently. In our study, eNOS VNTR and Hp polymorphisms appear to have the strongest associations with DIND and radiographic vasospasm, respectively.

Endovascular perforation subarachnoid hemorrhage fails to cause Morris water maze deficits in the mouse

Cognitive dysfunction is the primary driver of poor long-term outcome in aneurysmal subarachnoid hemorrhage (SAH) survivors; modeling such deficits preclinically is thus key for mechanistic and translational investigation. Although rat SAH causes long-term deficits in learning and memory, it remains unknown whether similar deficits are seen in the mouse, a species particularly amenable to powerful, targeted genetic manipulation. We thus subjected mice to endovascular perforation SAH and assessed long-term cognitive outcome via the Morris water maze (MWM), the most commonly used metric for rodent neurocognition. No significant differences in MWM performance (by either of two protocols) were seen in SAH versus sham mice. Moreover, SAH caused negligible hippocampal CA1 injury. These results undercut the potential of commonly used methods (of SAH induction and assessment of long-term neurocognitive outcome) for use in targeted molecular studies of SAH-induced cognitive deficits in the mouse.

Biomarkers as outcome predictors in subarachnoid hemorrhage--a systematic review

CONTEXT

Subarachnoid hemorrhage (SAH) has a high fatality rate and many suffer from delayed neurological deficits. Biomarkers may aid in the identification of high-risk patients, guide treatment/management and improve outcome.

OBJECTIVE

The aim of this review was to summarize biomarkers of SAH associated with outcome.

METHODS

An electronic database query was completed, including an additional review of reference lists to include all potential human studies.

RESULTS

A total of 298 articles were identified; 112 were reviewed; 55 studies were included.

CONCLUSION

This review details biomarkers of SAH that correlate with outcome. It provides the basis for research investigating their possible translation into the management of SAH patients.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Apolipoprotein E in Alzheimer's disease and other neurological disorders

Apolipoprotein E (APOE) is a 299-aminoacid protein encoded by the APOE gene. Three common polymorphisms in the APOE gene, ɛ2, ɛ3, and ɛ4, result in a single aminoacid change in the APOE protein. APOE ɛ2, ɛ3, and ɛ4 alleles strongly alter, in a dose-dependent manner, the likelihood of developing Alzheimer's disease and cerebral amyloid angiopathy. In particular, APOE ɛ4 is associated with increased risk for Alzheimer's disease whereas APOE ɛ2 is associated with decreased risk. The effects of APOE genotype on risk of these diseases are likely to be mediated by differential effects of APOE on amyloid-β accumulation in the brain and its vasculature. Response to treatment for Alzheimer's disease might differ according to APOE genotype. Because convincing evidence ties the APOE genotype to risk of Alzheimer's disease and cerebral amyloid angiopathy, APOE has been studied in other neurological diseases. APOE ɛ4 is associated with poor outcome after traumatic brain injury and brain haemorrhage, although the mechanisms underlying these associations are unclear. The possibility that APOE has a role in these and other neurological diseases has been of great interest, but convincing associations have not yet emerged.

Association of apolipoprotein E polymorphisms with cerebral vasospasm after spontaneous subarachnoid hemorrhage

Cerebral vasospasm (CVS) is the main complication of spontaneous subarachnoid hemorrhage (SAH), severely affecting clinical outcome of patients with SAH. Apolipoprotein E gene (APOE) is associated with prognosis of spontaneous subarachnoid hemorrhage (SAH), and APOEε4 allele is reported to be apt to CVS after SAH. The current study aimed to investigate the association of APOE polymorphisms with CVS after SAH. One hundred and eighty-five patients with spontaneous SAH were recruited in the study. APOE genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). CVS was judged by Transcranial Doppler sonography (TCD) combined with patients' condition. χ2-test and logistic regression analysis were done by SPSS (version 11.5). The distributions of APOE genotypes and alleles matched Hardy-Weinberg Law. In 185 patients, 21 of 32 (65.7%) patients with APOEε4 allele showed CVS, which was significantly different from those without APOE ε4 allele (56 of 153 patients, 36.6%, P=0.022). However, neither the presence of ε2 nor ε3 was significantly different from those absent of it (P>0.05). Logistic regression analysis demonstrated that ApoEε4 allele was a risk factor (OR=2.842. 95% CI 1.072-6.124. P=0.019) to predispose to CVS after adjusting for age, sex, hypertension or not, hyperlipemia or not, Fisher grade, and Hunt-Hess grade after SAH. Our finding suggests that the patients with APOEε4 allele predispose to CVS after spontaneous SAH.

The role of apolipoprotein e in the pathological events following subarachnoid hemorrhage: a review

Subarachnoid hemorrhage (SAH) strikes individuals with devastating neurological results. Traditional viewpoints do not explain all the differences that are usually found in clinical practice. The role of genetic predisposition in SAH has recently been investigated. Particular attention has been paid to the apolipoprotein E (apoE) genotype. APOE genotype is a major prognostic factor in patient outcome after spontaneous aneurysmal SAH. In patients with SAH, the expression of the apoE ε4 allele is associated with a higher risk of negative outcome and delayed ischemia. Evidence from experimental and clinical studies confirms that apoE plays an important role in the pathological events after SAH. This article reviews related research and surveys the links between the pathological events of SAH and apoE.

The apolipoprotein E ε4 allele and outcome in severe traumatic brain injury treated by an intracranial pressure–targeted therapy

Object

In this paper, the authors' goal was to study the influence of the apolipoprotein E ε4 allele on the clinical outcome in patients treated for severe traumatic brain injury (TBI) with an intracranial pressure (ICP)–targeted therapy based on the Lund concept.

Methods

The authors conducted a prospective double-blinded randomized trial in which they examined patients with severe TBI. Inclusion criteria consisted of a Glasgow Coma Scale (GCS) score ≤ 8 at the time of intubation and sedation, patient age between 15 and 70 years, an initial cerebral perfusion pressure > 10 mm Hg, and arrival to the hospital < 24 hours after trauma. Blood samples for the analysis of apolipoprotein E allele types were collected. Independent staff members evaluated outcomes by obtaining Glasgow Outcome Scale (GOS) scores at 3, 12, and 24 months.

Results

The occurrence of the ε4 allele was analyzed in 46 patients (mean age 35 ± 2.2 years with a median GCS score of 6 [range 3–8]). The ε4 allele was present in 39.1% of the patients. The ICP, cerebral perfusion pressure, and injury severity score were not statistically significantly different between the groups. The median GOS score at 3 months was 3.5, and at 12 and 24 months was 4 (range 1–5). Except for the GOS score at 3 months, which was dichotomized as favorable (GOS Score 4 or 5) and unfavorable (GOS Scores 1–3), no statistically significant differences in outcome, irrespective of GOS dichotomization used, were found between the patients with the ε4 allele and those without. The presence of the ε4 allele did not predict for clinical outcome, but GCS and ICP did.

Conclusions

The presence of ε4 is not associated with long-term clinical outcome in patients with severe TBI treated with an ICP targeted therapy, based on the Lund concept.

Genetic determinants of cerebral vasospasm, delayed cerebral ischemia, and outcome after aneurysmal subarachnoid hemorrhage

Despite extensive effort to elucidate the cellular and molecular bases for delayed cerebral injury after aneurysmal subarachnoid hemorrhage (aSAH), the pathophysiology of these events remains poorly understood. Recently, much work has focused on evaluating the genetic underpinnings of various diseases in an effort to delineate the contribution of specific molecular pathways as well as to uncover novel mechanisms. The majority of subarachnoid hemorrhage genetic research has focused on gene expression and linkage studies of these markers as they relate to the development of intracranial aneurysms and their subsequent rupture. Far less work has centered on the genetic determinants of cerebral vasospasm, the predisposition to delayed cerebral injury, and the determinants of ensuing functional outcome after aSAH. The suspected genes are diverse and encompass multiple functional systems including fibrinolysis, inflammation, vascular reactivity, and neuronal repair. To this end, we present a systematic review of 21 studies suggesting a genetic basis for clinical outcome after aSAH, with a special emphasis on the pathogenesis of cerebral vasospasm and delayed cerebral ischemia. In addition, we highlight potential pitfalls in the interpretation of genetic association studies, and call for uniformity of design of larger multicenter studies in the future.

Effect of apolipoprotein E genotype on the outcome after anterior cervical decompression and fusion in patients with cervical spondylotic myelopathy

Object

The authors examined a possible association between apolipoprotein E (APOE) gene polymorphism and the outcome after anterior microsurgical decompression in patients with cervical spondylotic myelopathy (CSM).

Methods

The authors conducted a prospective study of 60 consecutive patients (40 men, 20 women) with CSM who underwent anterior microsurgical decompression. The patients ranged in age from 26 to 86 years (mean 61.5 ± 14.6 years). Neurological deficits were classified according to the modified Japanese Orthopaedic Association Scale. Mean follow-up was 18.8 ± 4.6 months and APOE genotyping was carried out by isolation of DNA from venous blood samples. The APOE genotypes were determined by polymerase chain reaction followed by restriction enzyme digestion and polyacrylamide gel electrophoresis of digested fragments. Categorical variables were analyzed with the chi-square test, continuous data with the Mann-Whitney U-test, and for multiple groups with the Kruskal-Wallis H-test. A backward stepwise binary logistic regression analysis was performed to determine the effect of APOE in a multivariate model.

Results

Of the 60 patients with CSM, 35 (58.3%) improved and 25 (41.7%) did not improve or suffered deterioration (no-improvement group). In the improvement group 5 patients (8.3%) possessed the ε4 allele compared with 16 patients (26.7%) in the no-improvement group (p = 0.002, OR 3.3, 95% CI 1.7–6.1). In a multivariate model, the occurrence of the ε4 allele was a significant independent predictor for no improvement after anterior decompression and fusion (p = 0.004, OR 8.6, 95% CI 5.1–20.6).

Conclusions

The results of this study show that APOE gene polymorphism influences the short-term outcome of CSM patients after surgical decompressive and stabilizing therapy in the way that the presence of the APOE ε4 allele is an independent predictor for a no improvement. The presence of APOE may explain in part the different responses to operative therapies in patients with cervical myelopathy.

Significance of apolipoprotein E in subarachnoid hemorrhage: neuronal injury, repair, and therapeutic perspectives--a review

Subarachnoid hemorrhage (SAH) strikes individuals at a young age with devastating neurologic consequences. Classic formulations that correlate complications and outcome with clinical variables do not explain all the heterogeneity that is usually found in clinical practice. The role of genetic predisposition has recently been investigated. Particular attention has been paid to the apolipoprotein E (APOE) genotype that encodes for a polymorphic protein existing as 3 isoforms (apoE2, apoE3, apoE4), products of alleles E2, E3, and E4 at a single gene locus. ApoE is produced by astrocytes and exerts complex neuroprotective functions that make it a hub of the biochemical network of SAH. The neuroprotective effectiveness of the apoE4 isoform is reduced with respect to the others and this has made the E4 allele a risk factor candidate. Recently published observational studies and meta-analyses suggested that the APOE genotype may strongly improve the usual predictive model with the possibility of optimizing clinical decisions according to the individual's needs. Furthermore, the clinical results, together with new biological insights, suggest that SAH may be a possible candidate for the ongoing research on apoE-based neuroprotective therapy. This article reviews the clinical studies, analyzes their methodology, and surveys the biological links between the physiopathology of SAH and apoE and the possible prospects.

Psychosocial and neurocognitive performance after spontaneous nonaneurysmal subarachnoid hemorrhage related to the APOE-ε4 genotype: a prospective 5-year follow-up study

Object

In this study, the authors prospectively evaluated long-term psychosocial and neurocognitive performance in patients suffering from nonaneurysmal, nontraumatic subarachnoid hemorrhage (SAH) and investigated the association between the APOE-ε4 genotype and outcome in these patients.

Methods

All patients admitted to the authors' institution between January 2001 and January 2003 with spontaneous nonaneurysmal SAH were prospectively examined (mean follow-up 59.8 months). The APOE genotype was determined in all patients by polymerase chain reaction from a blood sample. Of the 30 patients included in this study, 11 were carriers of the ε4 allele.

Results

All patients showed a good recovery and regained full independence with no persisting neurological deficits. The patients with the ε4 allele, however, scored significantly higher on the Beck Depression Inventory (22.1 ± 6.3 vs 14.1 ± 5.1). At follow-up, depression was more persistent in the group with the ε4 allele compared with the group that lacked the allele. This finding reached statistical significance (p < 0.05). Selective attention was impaired in all patients during the first year of follow-up, with an earlier recovery noted in the patients without the ε4 allele. Moreover, there was a tendency toward a linear relationship between the Beck Depression Inventory and the d2 Test of Attention. Two patients who carried the ε4 allele did not return to their employment even after 5 years.

Conclusions

The findings in this study suggest that the APOE genotypes may be associated with the psychosocial and neurocognitive performance after spontaneous nonaneurysmal SAH, even in the absence of neurological impairment. Physicians should consider patient genotype in assessing the long-term consequences of nonaneurysmal SAH.

APOE genotype and functional outcome following aneurysmal subarachnoid hemorrhage

Apolipoprotein E (apoE), the major apolipoprotein in the central nervous system, has been shown to influence neurologic disease progression and response to neurologic injury in a gene-specific manner. Presence of the APOE4 allele is associated with poorer response to traumatic brain injury and ischemic stroke, but the association between APOE genotype and outcome following aneurysmal subarachnoid hemorrhage (SAH) remains unclear. The purpose of this project was to investigate the association between APOE genotype and outcome after SAH. We also explored the association of APOE4 genotype and cerebral vasospasm (CV) presence in a subsample of our population with available angiographic data. A sample of 206 aneurysmal SAH participants had APOE genotyping performed, Glasgow outcome scores (GOS) and modified Rankin scores (MRS) collected at 3 and 6 months after aneurysm rupture. No significant association was found between the presence of the APOE4 genotype and functional outcomes controlling for age, race, size of hemorrhage (Fisher grade), and severity of injury (Hunt & Hess grade). However when controlling for CV and the covariates listed above, individuals with the APOE4 allele had worse functional outcomes at both time points. The presence of the APOE2 allele was not associated with functional outcomes even when considering presence of CV. There was no difference in mortality associated with APOE4 presence, APOE2 presence, or presence of CV. These findings suggest APOE4 allele is associated with poor outcome after aneurysmal SAH.

Apolipoprotein E gene polymorphism and the risk of cervical myelopathy in patients with chronic spinal cord compression

STUDY DESIGN

Prospective evaluation of apolipoprotein E (APOE) genotypes in 106 consecutive patients with stenosis of the cervical spinal canal.

OBJECTIVE

To determine the association between cervical spondylotic myelopathy (CSM) in patients with chronic spinal cord compression and the APOE genotype.

SUMMARY OF BACKGROUND DATA

The APOE allele epsilon 4 is a risk factor for the occurrence, progression, and poor outcome in several neurologic diseases. Information of the association between APOE genotype and CSM in the literature are lacking so far.

METHODS

One hundred six consecutive patients with chronic cervical spinal cord compression due to stenosis of the spinal canal were evaluated prospectively. APOE genotypes were determined by polymerase chain reaction followed by restriction enzyme digestion and sodiumdodecylsulfate poyacrylamide gel electrophoresis (SDS PAGE) of digested fragments. Clinical and radiologic variables evaluated were age, occurrence of CSM, duration of symptoms, number of affected segments, and diameter of spinal canal of most affected segment. Univariate association between variables was tested. A backward stepwise method was used to construct multivariate logistic regression models in relation to the occurrence of CSM as dependent variable.

RESULTS

The following distribution of APOE genotypes was found: epsilon 2 epsilon 2 3 patients (2.8%), epsilon 2 epsilon 3 9 patients (8.5%), epsilon 2 epsilon 4 1 patient (0.9), epsilon 3 epsilon 3 67 patients (63.2%), epsilon 3 epsilon 4 24 patients (22.6%), epsilon 4 epsilon 4 2 patients (1.9%). Univariate analysis showed that patients with chronic spinal cord compression and homo- or heterozygous allele epsilon 4 are more likely to develop CSM than patients without allele epsilon 4 (65.0% vs. 35.0%, P < 0008; OR 3.5; 95% CI 1.3-9.8). This effect remained significant in a binary logistic regression model adjusted to other known risk factors for CSM. Inclusion of the variable homo- or heterozygous epsilon 4 allele led to an increased goodness of fit of the model compared with the model without epsilon 4. CONCLUSION.: This study supports the hypothesis that the APOE epsilon 4 allele increases the risk of CSM in patients with chronic cervical spinal cord compression; however, a larger prospective population-based study is needed to answer this question definitively.

Apolipoprotein E and neurological disease: therapeutic potential and pharmacogenomic interactions

The apolipoprotein E (apoE) polymorphism is emerging as a uniquely important genetic modifier that affects functional outcome from both acute and chronic neurological injuries. Recent attention has focused on common denominator mechanisms by which apoE might affect brain injury and/or brain repair responses in clinically diverse diseases. Although endogenous apoE likely serves several adaptive functions in the injured CNS, there is growing evidence that its effect on modifying brain inflammatory responses and providing protection from excitotoxic injury may be central to its protective properties. A more complete understanding of the role that apoE plays in the injured brain has led to novel therapeutic strategies for both acute and chronic neurological disease.

Lack of association between the apolipoprotein E gene and aneurysmal subarachnoid hemorrhage in an Italian population

OBJECT

The results of genome-wide scan studies have suggested the presence of a genetic risk factor for aneurysmal subarachnoid hemorrhage (SAH) on chromosome 19 (at 19p13). The apolipoprotein E (APOE) gene is located in this chromosomal region and encodes a protein that exerts several neuroprotective and neurotrophic functions in the brain. The purpose of this study was to evaluate whether a particular allele or genotype of the APOE gene would modify the occurrence or the clinical features of SAH.

METHODS

Genomic DNA was extracted from 146 patients with aneurysmal SAH and 222 age- and sex-matched healthy controls and genotyped for the triallelic polymorphism of the APOE gene (epsilon2, epsilon3, and epsilon4). Allele and genotype frequencies were compared between patients and controls. The clinical characteristics of the disease were compared according to the different APOE genotypes. Allele and genotype frequencies of the APOE gene polymorphism were nearly identical in cases and controls. Patients carrying the APOE epsilon4 allele had a significantly higher Hunt and Hess grade on admission (p = 0.0014). There was no significant relationship between any of the other clinical characteristics and the APOE genotype.

CONCLUSIONS

The authors' data do not support the hypothesis that genetic variations within the APOE gene are associated with aneurysmal SAH. However, the APOE gene influences the disease phenotype and may be regarded as a disease modifier gene.

Effects of apolipoprotein E genotype on outcome after ischaemic stroke, intracerebral haemorrhage and subarachnoid haemorrhage

BACKGROUND

Rodent models of acute ischaemic stroke and head injury suggest that apolipoprotein E (APOE) genotype influences neuronal repair, regeneration and survival after brain injury. Possession of an APOE epsilon4 allele is associated with poor outcome after head injury in clinical studies. APOE might therefore influence outcome after acute stroke in humans.

OBJECTIVE AND METHODS

To comprehensively search, identify, assess and carry out meta-analyses of studies reporting on the association between APOE and the combined outcome of death or dependency, or death alone, several months after ischaemic stroke, intracerebral haemorrhage (ICH) or subarachnoid haemorrhage (SAH).

RESULTS

Main analyses included data from nine studies on 2262 patients (1453 with ischaemic stroke, 199 with ICH and 610 with SAH). Overall, epsilon4+ genotypes were not significantly associated with risk of death or dependency several months after stroke. However, there was significant heterogeneity between studies, and between the three pathological types of stroke. Epsilon4+ genotypes were associated with increased death or dependency after SAH (relative risk (RR) 1.40, 95% confidence interval (CI) 1.06 to 1.84), with a trend towards a similar association with ICH (RR 1.38, 95% CI 0.99 to 1.92), but not with ischaemic stroke (RR 0.98, 95% CI 0.85 to 1.12). Results were similar for death alone.

CONCLUSIONS

APOE may differentially affect outcome after the three main pathological types of stroke. Further, large studies are needed to confirm or refute these findings, and to assess the possibility of an interaction between the effects of APOE and age.

Reported alcohol consumption and cognitive decline: The northern Manhattan study

BACKGROUND

Moderate alcohol intake may slow cognitive decline, and both vascular and neurodegenerative mechanisms have been implicated.

METHODS

We examined reported alcohol intake and cognitive decline in a community-based cohort of Hispanic, black and white individuals (n = 1,428). The role of the apolipoprotein E epsilon4 (APOE4) allele as a modifier was also studied.

RESULTS AND CONCLUSIONS

Reported drinking was as follows: 300 participants (21%) were 'never' drinkers, 622 (44%) 'past' drinkers, 145 (10%) reported taking less than 1 drink weekly, 330 (23%) 1 drink weekly up to 2 daily and 31 (2%) more than 2 drinks daily. A positive relationship was seen between reported alcohol intake and cognition. Drinking less than 1 drink a week (p = 0.09), between 1 drink weekly up to 2 drinks daily (p = 0.001) and more than 2 drinks daily (p = 0.003) were associated with less cognitive decline on the modified Telephone Interview for Cognitive Status compared to never drinkers. This dose-response relationship was not modified by the presence of an APOE4 allele in a subsample.

Bilirubin oxidation products (BOXes) and their role in cerebral vasospasm after subarachnoid hemorrhage

Many factors have been postulated to cause delayed subarachnoid hemorrhage (SAH)-induced vasospasm, including hemoglobin, nitric oxide, endothelin, and free radicals. We propose that free radicals (because of the high levels that are produced in the blood clots surrounding blood vessels after SAH) act on bilirubin, biliverdin, and possibly heme to produce BOXes (Bilirubin OXidized Products). Bilirubin oxidation products act on vascular smooth muscle cells to produce chronic vasoconstriction and vasospasm combined with a vasculopathy because of smooth muscle cell injury. This review summarizes recent evidence that BOXes play a role in SAH-induced vasospasm. The data supporting a role for BOXes includes (1) identification of molecules in cerebrospinal fluid (CSF) of patients with vasospasm after SAH that have structures consistent with BOXes; (2) BOXes are vasoactive in vitro and mimic the biochemical actions of CSF of patients with vasospasm; (3) BOXes are vasoactive in vivo, constricting rat cerebral vessels; and (4) there is a correlation between clinical occurrence of vasospasm and BOXes concentration in our preliminary study of patients with SAH. Since oxidation of bilirubin, biliverdin, and perhaps heme is proposed to produce BOXes that contribute to vasospasm, either blocking bilirubin formation, inactivating bilirubin or BOXes, or removing all of the blood clot before vasospasm are potential treatment targets.

Dissociation between vasospasm and functional improvement in a murine model of subarachnoid hemorrhage

OBJECT

The efficacy of nimodipine was examined in a murine model of subarachnoid hemorrhage (SAH). End points included the diameter of the lumen of the middle cerebral artery (MCA) and behavioral outcome. An apolipoprotein E (apoE)-mimetic peptide, acetyl-AS-Aib-LRKL-Aib-KRLL-amide, previously shown to have promise in this model was tested both alone and in combination with nimodipine. The effects of carboxyamidotriazole (CAI), a non-voltage-gated calcium channel blocker, were explored using the same animal paradigm.

METHODS

Experimental SAH was induced in male C57B1/6J mice. For 3 days postoperatively, behavioral analyses were performed. In the first experiment, the mice were treated with vehicle or with low- or high-dose CAI for 3 days. In the second experiment, the mice were treated with vehicle, high- and low-dose nimodipine, and/or the apoE-mimetic peptide. On postoperative Day 3 each mouse was killed and perfused. Following this, the right MCA was removed and its lumen measured. Mice that received nimodipine demonstrated significant behavioral improvements when compared with vehicle-treated mice, but there was no clear dose-dependent effect on MCA diameter. Administration of the apoE-mimetic peptide was associated with improved functional performance and a significant reduction in vasospasm. Mice that received high-dose CAI performed worse on functional tests, despite a significant increase in the diameters of their MCA lumina.

CONCLUSIONS

These results demonstrate a dissociation between vasospasm and neurological outcomes that is consistent with findings of previous clinical trials.

Update on evidence for a genetic predisposition to cerebral vasospasm

✓ Considerable evidence links cerebral vasospasm to the decreased bioavailability of endothelial nitric oxide synthase (eNOS) after aneurysmal subarachnoid hemorrhage (SAH). In recent studies from the cardiology literature, researchers have suggested that a genetic predisposition to coronary vasospasm might develop as the result of a T-786C single nucleotide polymorphism (SNP) in the eNOS gene. The authors of this study attempted to determine if there may be a similar genetic predisposition toward cerebral vasospasm.

The authors prospectively identified 28 patients with Fisher Grade 3 SAH from a group of 51 consecutive patients with ruptured intracranial saccular aneurysms. Genomic DNA was isolated from a peripheral blood sample obtained with permission from each patient. Gene microarray technology was used to assay the samples for the presence and distribution of certain key eNOS gene polymorphisms. Clinical, radiological, and genomic data were analyzed. The finding of eNOS T-786C SNP could be used to significantly differentiate between the presence and severity of cerebral vasospasm (p = 0.04).

The findings from this preliminary study support similar findings in the coronary vasospasm literature as well as the hypothesis that a predisposition toward cerebral vasospasm may be related partially to genetic factors, which needs to be confirmed in a larger study. Such gene-based information may be important in rapidly identifying patients at increased risk of vasospasm after SAH, independent of their Fisher grade. In this article, the authors review key studies in this area.

Genetic Factors in Outcome After Traumatic Brain Injury

It is becoming increasingly clear that genetic factors modify outcome after traumatic brain injury (TBI). The best known example of this is the association between the apolipoprotein E4 allele (APOE epsilon4) and poorer outcomes. However, our knowledge of the many other genes that might influence outcome is still in its infancy. This article will review the basic principles underlying recent advances in genetics, and then describe the current state of knowledge regarding the impact of genetic factors on TBI outcome. We conclude that although genetic advances have implications for prognosis, their biggest contribution will be to elucidate the pathophysiology of TBI, potentially leading to new treatments.