Genetic variation of the APOE promoter and outcome after head injury

Concussion-Associated Gene Variant COMT rs4680 Is Associated With Elite Rugby Athlete Status

OBJECTIVE

Concussions are common match injuries in elite rugby, and reports exist of reduced cognitive function and long-term health consequences that can interrupt or end a playing career and produce continued ill health. The aim of this study was to investigate the association between elite rugby status and 8 concussion-associated risk polymorphisms. We hypothesized that concussion-associated risk genotypes and alleles would be underrepresented in elite rugby athletes compared with nonathletes.

DESIGN

A case-control genetic association study.

SETTING

Institutional (university).

PARTICIPANTS

Elite White male rugby athletes [n = 668, mean (SD) height 1.85 (0.07) m, mass 102 (12) kg, and age 29 (7) years] and 1015 nonathlete White men and women (48% men).

INTERVENTIONS

Genotype was the independent variable, obtained by PCR of genomic DNA using TaqMan probes.

MAIN OUTCOME MEASURE

Elite athlete status with groups compared using χ 2 and odds ratio (OR).

RESULTS

The COMT rs4680 Met/Met (AA) genotype, Met allele possession, and Met allele frequency were lower in rugby athletes (24.8%, 74.6%, and 49.7%, respectively) than nonathletes (30.2%, 77.6%, and 54.0%; P < 0.05). The Val/Val (GG) genotype was more common in elite rugby athletes than nonathletes (OR 1.39, 95% confidence interval 1.04-1.86). No other polymorphism was associated with elite athlete status.

CONCLUSIONS

Elite rugby athlete status is associated with COMT rs4680 genotype that, acting pleiotropically, could affect stress resilience and behavioral traits during competition, concussion risk, and/or recovery from concussion. Consequently, assessing COMT rs4680 genotype might aid future individualized management of concussion risk among athletes.

Concussion-Associated Polygenic Profiles of Elite Male Rugby Athletes

Due to the high-velocity collision-based nature of elite rugby league and union, the risk of sustaining a concussion is high. Occurrence of and outcomes following a concussion are probably affected by the interaction of multiple genes in a polygenic manner. This study investigated whether suspected concussion-associated polygenic profiles of elite rugby athletes differed from non-athletes and between rugby union forwards and backs. We hypothesised that a total genotype score (TGS) using eight concussion-associated polymorphisms would be higher in elite rugby athletes than non-athletes, indicating selection for protection against incurring or suffering prolonged effects of, concussion in the relatively high-risk environment of competitive rugby. In addition, multifactor dimensionality reduction was used to identify genetic interactions. Contrary to our hypothesis, TGS did not differ between elite rugby athletes and non-athletes (p ≥ 0.065), nor between rugby union forwards and backs (p = 0.668). Accordingly, the TGS could not discriminate between elite rugby athletes and non-athletes (AUC ~0.5), suggesting that, for the eight polymorphisms investigated, elite rugby athletes do not have a more ‘preferable’ concussion-associated polygenic profile than non-athletes. However, the COMT (rs4680) and MAPT (rs10445337) GC allele combination was more common in rugby athletes (31.7%; p < 0.001) and rugby union athletes (31.8%; p < 0.001) than non-athletes (24.5%). Our results thus suggest a genetic interaction between COMT (rs4680) and MAPT (rs10445337) assists rugby athletes in achieving elite status. These findings need exploration vis-à-vis sport-related concussion injury data and could have implications for the management of inter-individual differences in concussion risk.

Apolipoprotein E4 Polymorphism and Outcomes from Traumatic Brain Injury: A Living Systematic Review and Meta-Analysis

The mortality of traumatic brain injury (TBI) has been largely static despite advances in monitoring and imaging techniques. Substantial variance exists in outcome, not fully accounted for by baseline characteristics or injury severity, and genetic factors likely play a role in this variance. The aims of this systematic review were to examine the evidence for a link between the apolipoprotein E4 (APOE4) polymorphism and TBI outcomes and where possible, to quantify the effect size via meta-analysis. We searched EMBASE, MEDLINE, CINAHL, and gray literature in December 2017. We included studies of APOE genotype in relation to functional adult TBI outcomes. Methodological quality was assessed using the Quality in Prognostic Studies Risk of Bias Assessment Instrument and the prognostic studies adaptation of the Grading of Recommendations Assessment, Development and Evaluation tool. In addition, we contacted investigators and included an additional 160 patients whose data had not been made available for previous analyses, giving a total sample size of 2593 patients. Meta-analysis demonstrated higher odds of a favorable outcome following TBI in those not possessing an ApoE ɛ4 allele compared with ɛ4 carriers and homozygotes (odds ratio 1.39, 95% confidence interval 1.05 to 1.84; p = 0.02). The influence of APOE4 on neuropsychological functioning following TBI remained uncertain, with multiple conflicting studies. We conclude that the ApoE ɛ4 allele confers a small risk of poor outcome following TBI, with analysis by TBI severity not possible based on the currently available published data. Further research into the long-term neuropsychological impact and risk of dementia is warranted.

A global collaboration to study intimate partner violence-related head trauma: The ENIGMA consortium IPV working group

Intimate partner violence includes psychological aggression, physical violence, sexual violence, and stalking from a current or former intimate partner. Past research suggests that exposure to intimate partner violence can impact cognitive and psychological functioning, as well as neurological outcomes. These seem to be compounded in those who suffer a brain injury as a result of trauma to the head, neck or body due to physical and/or sexual violence. However, our understanding of the neurobehavioral and neurobiological effects of head trauma in this population is limited due to factors including difficulty in accessing/recruiting participants, heterogeneity of samples, and premorbid and comorbid factors that impact outcomes. Thus, the goal of the Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) Consortium Intimate Partner Violence Working Group is to develop a global collaboration that includes researchers, clinicians, and other key community stakeholders. Participation in the working group can include collecting harmonized data, providing data for meta- and mega-analysis across sites, or stakeholder insight on key clinical research questions, promoting safety, participant recruitment and referral to support services. Further, to facilitate the mega-analysis of data across sites within the working group, we provide suggestions for behavioral surveys, cognitive tests, neuroimaging parameters, and genetics that could be used by investigators in the early stages of study design. We anticipate that the harmonization of measures across sites within the working group prior to data collection could increase the statistical power in characterizing how intimate partner violence-related head trauma impacts long-term physical, cognitive, and psychological health.

Genetic Factors That Could Affect Concussion Risk in Elite Rugby

Elite rugby league and union have some of the highest reported rates of concussion (mild traumatic brain injury) in professional sport due in part to their full-contact high-velocity collision-based nature. Currently, concussions are the most commonly reported match injury during the tackle for both the ball carrier and the tackler (8-28 concussions per 1000 player match hours) and reports exist of reduced cognitive function and long-term health consequences that can end a playing career and produce continued ill health. Concussion is a complex phenotype, influenced by environmental factors and an individual's genetic predisposition. This article reviews concussion incidence within elite rugby and addresses the biomechanics and pathophysiology of concussion and how genetic predisposition may influence incidence, severity and outcome. Associations have been reported between a variety of genetic variants and traumatic brain injury. However, little effort has been devoted to the study of genetic associations with concussion within elite rugby players. Due to a growing understanding of the molecular characteristics underpinning the pathophysiology of concussion, investigating genetic variation within elite rugby is a viable and worthy proposition. Therefore, we propose from this review that several genetic variants within or near candidate genes of interest, namely APOE, MAPT, IL6R, COMT, SLC6A4, 5-HTTLPR, DRD2, DRD4, ANKK1, BDNF and GRIN2A, warrant further study within elite rugby and other sports involving high-velocity collisions.

Genetic polymorphisms associated with the risk of concussion in 1056 college athletes: a multicentre prospective cohort study

BACKGROUND/AIM

To evaluate the association of genetic polymorphisms APOE, APOE G-219T promoter, microtubule associated protein(MAPT)/tau exon 6 Ser⁵³Pro, MAPT/tau Hist⁴⁷Tyr, IL-6572 G/C and IL-6R^Asp358^Ala with the risk of concussion in college athletes.

METHODS

A 23-centre prospective cohort study of 1056 college athletes with genotyping was completed between August 2003 and December 2012. All athletes completed baseline medical and concussion questionnaires, and post-concussion data were collected for athletes with a documented concussion.

RESULTS

The study cohort consisted of 1056 athletes of mean±SD age 19.7±1.5 years, 89.3% male, 59.4% Caucasian, 35.0% African-American, 5.6% other race. The athletes participated in American football, soccer, basketball, softball, men's wrestling and club rugby. A total of 133 (12.1% prevalence) concussions occurred during an average surveillance of 3 years per athlete. We observed a significant positive association between IL-6R CC (p=0.001) and a negative association between APOE4 (p=0.03) and the risk of concussion. Unadjusted and adjusted logistic regression analysis showed a significant association between IL-6R CC and concussion (OR 3.48; 95% CI 1.58 to 7.65; p=0.002) and between the APOE4 allele and concussion (OR 0.61; 95% CI 0.38 to 0.96; p=0.04), which persisted after adjustment for confounders.

CONCLUSIONS

IL-6R CC was associated with a three times greater concussion risk and APOE4 with a 40% lower risk.

Systematic Review of Genetic Risk Factors for Sustaining a Mild Traumatic Brain Injury

This systematic review examined the association between genetics and risk for sustaining a traumatic brain injury. We retrieved articles published in English from 1980 to July 2016 obtained from the online databases PubMed, PsycINFO®, MEDLINE®, Embase, and Web of Science. In total 5903 articles were identified, 77 underwent full-text screening, and 6 were included in this review. Five studies examined the risk of concussion associated with apolipoprotein E alleles (APOE-ɛ2, ɛ3,ɛ4), and polymorphisms of the APOE promoter (rs405509), brain derived neurotrophic factor (BDNF, rs6265), and dopamine receptor D2 (DRD2, rs1800497) were each considered in two studies. Microtubule associated protein tau (TAU exon 6 polymorphisms His47Tyr [rs2258689] and Ser53Pro [rs10445337]), and neurofilament heavy (NEHF, rs165602) genotypic variants, were the focus of single studies. No study showed an increased risk associated solely with the presence of the APOE-ɛ4 allele, nor were there any significant findings for the NEFH, TAU, or DRD2 genotypic variants. Two studies examined the APOE promoter -219G/T polymorphism in athletes, and both found an association with concussion. Both BDNF studies also found a significant association with concussion incidence; United States soldiers with the Met/Met genotype were more likely to report a history of concussion prior to deployment and to sustain a concussion during deployment. We conclude that the APOE promoter -219G/T polymorphism and the BDNF Met/Met genotype might confer risk for sustaining a TBI. Based on research to date, the APOE-ɛ4 allele does not appear to influence risk. More research is needed to determine if these findings replicate.

An association between polymorphisms within the APOE gene and concussion aetiology in rugby union players

OBJECTIVES

Concussion refers to changes in neurological function due to biomechanical forces transmitted to the head. The APOE ε4 allele is associated with brain injury severity. The objective was to determine if APOE gene variants are associated with concussion history and severity in rugby players.

DESIGN

In total, 128 non-concussed controls and 160 previously concussed participants (all cases N=160; diagnosed N=139) were recruited from high school (junior, N=121), club (N=116) and professional rugby teams (N=51).

METHODS

Participants were genotyped for rs405509 (G>T), rs429358 (T>C) and rs7412 (C>T) APOE variants. Statistical analyses were performed using the R environment.

RESULTS

The rs405509 TT genotype was over-represented in controls compared to all cases (P=0.043; control: 29%, all cases: 18%; odds ratio: 0.55, 95% confidence interval 0.31-0.98). The APOE-ε isoform frequencies were not significantly different between groups (P>0.05). Additionally, the inferred APOE (rs405509-ε2/ε3/ε4) T-ε3 haplotype was over-represented in controls (41%) compared to diagnosed (32%, P=0.042). The G-ε3 haplotype was under-represented in controls (36%) compared to all cases (44%, P=0.019) and diagnosed (44%, P=0.021). The TT genotype was significantly associated with rapid recovery (P=0.048, <1 week: 51%, N=70, ≥1 week: 36%, N=29; odds ratio: 0.55, 95% confidence interval 0.30-1.01).

CONCLUSIONS

These findings support the further elucidation of the APOE gene or closely-related genes in concussion aetiology. Although similar preliminary results were found when juniors were separately analysed, the under-powered sample size for junior subgroup requires future investigation in larger cohorts of junior-level athletes.

Applying Systems Biology Methodology To Identify Genetic Factors Possibly Associated with Recovery after Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality worldwide. It is linked with a number of medical, neurological, cognitive, and behavioral sequelae. The influence of genetic factors on the biology and related recovery after TBI is poorly understood. Studies that seek to elucidate the impact of genetic influences on neurorecovery after TBI will lead to better individualization of prognosis and inform development of novel treatments, which are considerably lacking. Current genetic studies related to TBI have focused on specific candidate genes. The objectives of this study were to use a system biology-based approach to identify biologic processes over-represented with genetic variants previously implicated in clinical outcomes after TBI and identify unique genes potentially related to recovery after TBI. After performing a systematic review to identify genes in the literature associated with clinical outcomes, we used the genes identified to perform a systems biology-based integrative computational analysis to ascertain the interactions between molecular components and to develop models for regulation and function of genes involved in TBI recovery. The analysis identified over-representation of genetic variants primarily in two biologic processes: response to injury (cell proliferation, cell death, inflammatory response, and cellular metabolism) and neurocognitive and behavioral reserve (brain development, cognition, and behavior). Overall, this study demonstrates the use of a systems biology-based approach to identify unique/novel genes or sets of genes important to the recovery process. Findings from this systems biology-based approach provide additional insight into the potential impact of genetic variants on the underlying complex biological processes important to TBI recovery and may inform the development of empirical genetic-related studies for TBI. Future studies that combine systems biology methodology and genomic, proteomic, and epigenetic approaches are needed in TBI.

Genetic findings in sport-related concussions: potential for individualized medicine?

Concussion is a traumatic transient disturbance of the brain. In sport, the initial time and severity of concussion is known giving an opportunity for subsequent analysis. Variability in susceptibility and recovery between individual athletes depends, among other parameters, on genetic factors. The genes-encoding polypeptides that determine incidence, severity and prognosis for concussion are the primary candidates for genetic analysis. Genetic polymorphisms in the genes contributing to plasticity and repair (APOE), synaptic connectivity (GRIN2A), calcium influx (CACNA1E), uptake and deposit of glutamate (SLC17A7) are potential biomarkers of concussion incidence and recovery rate. With catalogued genetic variants, prospective genotyping of athletes at the beginning of their career will allow medical professionals to improve concussion management and return-to-play decisions.

Gene sequences regulating the production of apoE and cerebral palsy of variable severity

BACKGROUND

The apoE protein is the most important lipid transporter in the brain and has also been shown to have several regulatory functions in the central nervous system. The production of apoE is regulated by a number of genes and increases under certain conditions such as cerebral injury in adults.

AIMS

Our aim was to study whether variations in genes regulating the expression of the APOE gene were associated with severity of cerebral palsy (CP).

METHODS

Children enrolled in the Cerebral Palsy Register of Norway (CPRN) were invited to participate in this cross-sectional study; 281 of the invited 703 children (40%) returned swabs with buccal cells collected by parents. Six genetic variations thought to affect the production of apoE were genotyped and correlated with clinical data recorded in the CPRN.

RESULTS

Compared with children carrying the GG allele, children with genotype GT or TT in a specific genetic variation (rs59007384 located in the nearby TOMM40 gene) had excess risk for worse fine motor function (Odds ratio (OR): 1.82; 95% Confidence interval (CI): 1.10-2.99; p = 0.019) and epilepsy (OR: 2.32; CI: 1.17-4.61; p = 0.016). There was no association between severity of CP and any of the other five genetic variations analyzed.

CONCLUSION

Our findings suggest that genetic variations in one of the sequences regulating the expression of APOE, may be associated with worse clinical outcome in children with cerebral palsy.

Post-Traumatic Brain Injury: Genetic Susceptibility to Outcome

It is estimated that 2% of the population from industrialized countries live with lifelong disabilities resulting from traumatic brain injury (TBI) and roughly one in four adults are unable to return to work 1 year after injury because of physical or mental disabilities. TBI is a significant public health issue that causes substantial physical and economical repercussions for the individual and society. Electronic databases (PubMed, Web of Science, Google Scholar) were searched with the keywords traumatic brain injury, TBI, genes and TBI, TBI outcome, head injury. Human studies on non-penetrating traumatic brain injuries reported in English were included. To provide health care workers with the basic information for clinical management we summarize and compare the data on post-TBI outcome with regard to the impact of genetic variation: apolipoprotein E (APOE), brain-derived neurotrophic factor (BDNF), calcium channel, voltage dependent P/Q type, catechol-O-methyltransferase (COMT), dopamine receptor D2 and ankyrin repeat and kinase domain containing 1 (DRD2 and ANKK1), interleukin-1 (IL-1), interleukin-6 (IL-6), kidney and brain expressed protein (KIBRA), neurofilament, heavy polypeptide (NEFH), endothelial nitric oxide synthase 3 (NOS3), poly (ADP-ribose) polymerase-1 (PARP-1), protein phosphatase 3, catalytic subunit, gamma isozyme (PPP3CC), the serotonin transporter (5-HTT) gene solute carrier family 6 member (SLC6A4) and tumor protein 53 (TP53). It is evident that contradicting results are attributable to the heterogeneity of studies, thus further researches are warranted to effectively assess a relation between genetic traits and clinical outcome following traumatic injuries.

Prognosis in severe brain injury

BACKGROUND

The prediction of neurologic outcome is a fundamental concern in the resuscitation of patients with severe brain injury.

OBJECTIVE

To provide an evidence-based update on neurologic prognosis following traumatic brain injury and hypoxic-ischemic encephalopathy after cardiac arrest.

DATA SOURCE

Search of the PubMed database and manual review of bibliographies from selected articles to identify original data relating to prognostic methods and outcome prediction models in patients with neurologic trauma or hypoxic-ischemic encephalopathy.

DATA SYNTHESIS AND CONCLUSION

Articles were scrutinized regarding study design, population evaluated, interventions, outcomes, and limitations. Outcome prediction in severe brain injury is reliant on features of the neurologic examination, anatomical and physiological changes identified with CT and MRI, abnormalities detected with electroencephalography and evoked potentials, and physiological and biochemical derangements at both the brain and systemic levels. Use of such information in univariable association studies generally lacks specificity in classifying neurologic outcome. Furthermore, the accuracy of established prognostic classifiers may be affected by the introduction of outcome-modifying interventions, such as therapeutic hypothermia following cardiac arrest. Although greater specificity may be achieved with scoring systems derived from multivariable models, they generally fail to predict outcome with sufficient accuracy to be meaningful at the single patient level. Discriminative models which integrate knowledge of genetic determinants and biologic processes governing both injury and repair and account for the effects of resuscitative and rehabilitative care are needed.

Genetics of cerebral vasospasm

Cerebral vasospasm (CV) is a major source of morbidity and mortality in aneurysmal subarachnoid hemorrhage (aSAH). It is thought that an inflammatory cascade initiated by extravasated blood products precipitates CV, disrupting vascular smooth muscle cell function of major cerebral arteries, leading to vasoconstriction. Mechanisms of CV and modes of therapy are an active area of research. Understanding the genetic basis of CV holds promise for the recognition and treatment for this devastating neurovascular event. In our review, we summarize the most recent research involving key areas within the genetics and vasospasm discussion: (1) Prognostic role of genetics—risk stratification based on gene sequencing, biomarkers, and polymorphisms; (2) Signaling pathways—pinpointing key inflammatory molecules responsible for downstream cellular signaling and altering these mediators to provide therapeutic benefit; and (3) Gene therapy and gene delivery—using viral vectors or novel protein delivery methods to overexpress protective genes in the vasospasm cascade.

Biomarkers, genetics, and risk factors for concussion

It is estimated that between 1.6 and 3.8 million concussions occur annually in the United States. Although frequently regarded as benign, concussions can lead to multiple different adverse outcomes, including prolonged postconcussive symptoms, chronic traumatic encephalopathy, cognitive impairment, early onset dementia, movement disorders, psychiatric disorders, motor neuron disease, and even death. Therefore it is important to identify individuals with concussion to provide appropriate medical care and minimize adverse outcomes. Furthermore, it is important to identify individuals who are predisposed to sustaining a concussion or to having an adverse outcome after concussion. This article will discuss the current research on serum biomarkers for concussion, genetic influence on concussion, risk factors associated with concussion predisposition and poor outcome, and practical suggestions for the application of this information in clinical practice.

Genetics and outcomes after traumatic brain injury (TBI): what do we know about pediatric TBI?

Human genetic association studies in individuals with traumatic brain injury (TBI) have increased rapidly over the past few years. Recently, several review articles evaluated the association of genetics with outcomes after TBI. However, almost all of the articles discussed in these reviews focused on adult TBI. The primary objective of this review is to gain a better understanding of which genes and/or genetic polymorphisms have been evaluated in pediatric TBI. Our initial search identified 113 articles. After review of these articles only 5 genetic association studies specific to pediatric TBI were identified. All five of these studies evaluated the apolipoprotein (APOE) gene. The study design and methods of these identified papers will be discussed. An additional search was then performed to evaluate genes beyond APOE that have been evaluated in adult TBI; findings from these studies are highlighted. Larger genetic studies will need to be performed in the future to better elucidate the association of APOE and other genes with outcomes after TBI in children. There is great potential to utilized genetic information to inform prognosis and management after TBI in children; however, we have much work ahead of us to reach the goal of individualized management.

Impact of injury location and severity on posttraumatic epilepsy in the rat: role of frontal neocortex

Human posttraumatic epilepsy (PTE) is highly heterogeneous, ranging from mild remitting to progressive disabling forms. PTE results in simple partial, complex partial, and secondarily generalized seizures with a wide spectrum of durations and semiologies. PTE variability is thought to depend on the heterogeneity of head injury and patient's age, gender, and genetic background. To better understand the role of these factors, we investigated the seizures resulting from calibrated fluid percussion injury (FPI) to adolescent male Sprague-Dawley rats with video electrocorticography. We show that PTE incidence and the frequency and severity of chronic seizures depend on the location and severity of FPI. The frontal neocortex was more prone to epileptogenesis than the parietal and occipital, generating earlier, longer, and more frequent partial seizures. A prominent limbic focus developed in most animals, regardless of parameters of injury. Remarkably, even with carefully controlled injury parameters, including type, severity, and location, the duration of posttraumatic apnea and the age and gender of outbred rats, there was great subject-to-subject variability in frequency, duration, and rate of progression of seizures, indicating that other factors, likely the subjects' genetic background and physiological states, have critical roles in determining the characteristics of PTE.

Apolipoprotein E genotype and concussion in college athletes

OBJECTIVE

To evaluate the association between apolipoprotein E (APOE) polymorphisms (E2, C/T Arg158Cys; E4, T/C Cys112Arg; and promoter, g-219t) and the history of concussion in college athletes. We hypothesized that carrying 1 or more APOE rare (or minor) allele assessed in this study would be associated with having a history of 1 or more concussions.

DESIGN

Multicenter cross-sectional study.

SETTING

University athletic facilities.

PARTICIPANTS

One hundred ninety-six male football (n = 163) and female soccer (n = 33) college athletes volunteered.

INTERVENTIONS

Written concussion history questionnaire and saliva samples for genotyping.

MAIN OUTCOME MEASURES

Self-reported history of a documented concussion and rare APOE genotype (E2, E4, promoter).

RESULTS

There was a significant association (Wald χ² = 3.82; P = 0.05; odds ratio = 9.8) between carrying all APOE rare alleles and the history of a previous concussion. There was also a significant association (Wald χ² = 3.96, P = 0.04, odds ratio = 8.4) between carrying the APOE promoter minor allele and experiencing 2 or more concussions.

CONCLUSIONS

Carriers of all 3 APOE rare (or minor) alleles assessed in this study were nearly 10 times more likely to report a previous concussion and may be at a greater risk of concussion versus noncarriers. Promoter minor allele carriers were 8.4 times more likely to report multiple concussions and may be at a greater risk of multiple concussions versus noncarriers. Research involving larger samples of individuals with multiple concussions and carriers of multiple APOE rare alleles is warranted.

Genetic association studies in patients with traumatic brain injury

Traumatic brain injury (TBI) constitutes a major cause of mortality and disability worldwide, especially among young individuals. It is estimated that despite all the recent advances in the management of TBI, approximately half of the patients suffering head injuries still have unfavorable outcomes, which represents a substantial health care, social, and economic burden to societies.

Considerable variability exists in the clinical outcome after TBI, which is only partially explained by known factors. Accumulating evidence has implicated various genetic elements in the pathophysiology of brain trauma. The extent of brain injury after TBI seems to be modulated to some degree by genetic variants.

The authors' current review focuses on the up-to-date state of knowledge regarding genetic association studies in patients sustaining TBI, with particular emphasis on the mechanisms underlying the implication of genes in the pathophysiology of TBI.

Genetic susceptibility to traumatic brain injury and apolipoprotein E gene

Traumatic brain injury (TBI) is defined as an injury caused by a blow or jolt to the head or a penetrating head injury that disrupts the normal function of the brain. It is a common emergency and severe case in neurosurgery field. Nowadays, there are more and more evidences showing that TBI, which is apparently similar in pathology and severity in the acute stage, may have different outcomes. The known prognostic factors (such as age, severity of injury and treatments, etc.) explain only part of this variability and the concept of genetic susceptibility of traumatic brain injury has already been accepted by more and more people. It is now demonstrated that genetic polymorphism may play a key role in the susceptibility to TBI, even outcome following TBI. Although there are many genes that may involved in pathophysiological processes influencing TBI, apolipoprotein E gene has become one of the most extensive studied genes in neurotrauma and neurodegenerative disease and seems to take an important part in the neural responses to TBI. In this article, we will review the current understanding of the genetic susceptibility of TBI and the advancements regarding the impact of apolipoprotein E genotype on the severity and/or outcome following TBI.

Meta-analysis of APOE4 allele and outcome after traumatic brain injury

There is conflicting evidence regarding a possible association between the apolipoprotein E4 (APOE4) allele and the consequences of traumatic brain injury (TBI). Our aim was to carry out a meta-analysis of cohort studies of sufficient rigor to determine whether the presence of the APOE4 allele contributes to initial injury severity and/or poor outcome following TBI. MEDLINE, EMBase, CBMdisc, and CNKI databases were searched for literature published from January 1993 to October 2007. Of the 100 identified studies, 14 cohort studies were selected for analysis based on comprehensive quality assessment using a standardized scale. Data from the 14 eligible cohort studies included a total of 2527 participants, 736 with and 1791 without the APOE4 allele. The APOE4 allele was not associated with initial injury severity of TBI. The pooled RR were 1.11 (95% confidence interval [CI], 0.91 to 1.35) for severe injury, 1.06 (95% CI, 0.86-1.31) for moderate injury and 0.93 (95% CI, 0.81-1.06) for mild injury. However, the APOE4 allele was significantly associated with a poor outcome of TBI at 6 months after injury (RR = 1.36; 95% CI, 1.04-1.78). The association remained significant in sensitivity tests. This meta-analysis indicates that the presence of the APOE4 allele is not associated with the initial severity of brain injury following TBI but is associated with increased risk of poor long-term outcome at 6 months after injury.

Correlation between APOE -491AA promoter in epsilon4 carriers and clinical deterioration in early stage of traumatic brain injury

The objective of this work was to investigate the relationship between apolipoprotein E (APOE) promoters (G-219T, C-427T, A-491T) polymorphisms and the clinical deterioration in early stage of traumatic brain injury (TBI) in a cohort of Chinese patients. In this study, we used the cohort of patients which has been reported previously. A total of 110 subjects with TBI (80 males and 30 females, with mean age of 43.87 years) were admitted from December 2003 to May 2004, and demographic and clinical data were collected. The clinical deterioration of patient's condition in acute stage (<7 days after TBI) was judged by either of the following criteria: decrease of Glasgow Coma Scale (GCS) score (compared with initial admission GCS), increase in hematoma volume or delayed hematoma both detected by repeated computed tomography (CT) scanning compared to that on admission. Venous blood was collected from patients with TBI on admission to determine the APOE promoter polymorphisms. The APOE genotyping was performed by means of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). chi(2) test and logistic regression analyses were done by SPSS. In 110 Chinese patients, the distributions of APOE genotypes and alleles matched Hardy-Weinberg Law, and 19 subjects presented with deteriorated clinical condition in acute stage after hospitalization. chi(2) test showed insignificant differences in association of APOE promoter polymorphisms with clinical deterioration (p>0.05). But logistic regression analyses, after adjusting patients' age, injury severity and injury mechanism etc, showed that -491AA (OR=11.681, p=0.009, 95%, CI 1.824-74.790) and APOE epsilon4 were all risk factors, with injury severity and alcohol-drinking as other risk factors. In Chinese population, as a significant but not independent risk factor, only APOE -491AA promoter in epsilon4 carriers is apt to the clinical deterioration and may contribute to the poor outcome after TBI.

APOE, APOE promoter, and Tau genotypes and risk for concussion in college athletes

OBJECTIVE

To investigate associations of APOE, APOE promoter (G-219T), and tau protein exon 6 polymorphisms (47 and 53) and a history of self-reported concussion in college athletes.

DESIGN

Multi-center cross-sectional study.

SETTING

Male football and male and female soccer programs at the University of South Carolina, Jacksonville University, Benedict College, and the College of Charleston.

PARTICIPANTS

Active 18- to 30-year-old (n = 195) intercollegiate male football players and male and female soccer players during 2001 and 2002.

ASSESSMENT OF RISK FACTORS

Written questionnaires and blood or mouthwash samples for DNA for genotyping by RFLP/PCR.

MAIN OUTCOME MEASUREMENT

Self-reported history of concussions over the previous 8 years.

RESULTS

A statistically significant, nearly 3-fold increase in risk of a history of concussion for those with the APOE promoter G-219T TT genotype relative to the GG genotype (OR, 2.8; 95% CI, 1.1 to 6.9) adjusted for age, sport, school, and years in their primary sport, a finding that was stronger for Cantu grade 2 and 3 concussions.

CONCLUSIONS

These results suggest that college athletes with an APOE promoter G-219T TT genotype may be at increased risk for having a history of concussions, especially more severe concussions. Although there was some support for the possibility that the tau 53 polymorphism may be associated with increased risk of prior concussion (OR, 2.1; 95% CI, 0.3 to 14.5), there was no support for an association with APOE genotypes. The results of this cross-sectional study support the need for a prospective study of genetic factors, such as APOE promoter polymorphisms, and the incidence of and sequelae from concussions in college athletes.

Lack of association between apolipoprotein E promoters in epsilon4 carriers and worsening on computed tomography in early stage of traumatic brain injury

We investigated the relationship between apolipoprotein E (APOE) promoters (G-219T, C-427T, A-491T) polymorphisms, and worsening CT results in early stage of traumatic brain injury (TBI) in a previously reported cohort of Chinese patients. Radiographic evidence of hemorrhage extension or delayed hemorrhage in acute stage (< 7 days after TBI) was judged by serial CT scanning compared to that on admission. APOE genotyping was performed by means of PCR-RFLP. Chi2 test and logistic regression analyses were done using SPSS software. Of 110 Chinese patients, 19 presented with deteriorated clinical condition in acute stage after hospitalization. Among these 19 patients, serial CT scanning revealed 3 cases with hemorrhage extension and 2 cases with delayed hemorrhage. Chi2 test showed no statistical differences in radiographic worsening/stabilization between the APOE epsilon4(+) and APOE epsilon4(-) groups (p = 0.170 > 0.05). Furthermore, no significant correlation between intracranial bleeding based on CT scanning with genotype or with haplotype frequencies for A-491T, C-427T, or G-219T was found by chi2 test (p > 0.05). In Chinese population, our data do not support the hypothesis that genetic variations within the APOE gene are associated with CT worsening in early stage of TBI.

‘Talk and Die’ patients presenting to a major trauma centre over a 10 year period: A critical review

'Talk and die patients' describes a small number of patients who present with a mild head injury (Glasgow Coma Scale [GCS] 13-15) and then subsequently deteriorate and die from intracranial causes. We analysed the medical records of all those adult patients whose primary diagnosis as the cause of death was head injury, as determined by the coroner, who were admitted to a major Australian trauma centre between January 1994 and December 2003 (a 10-year period). The clinical profile of those patients who fulfilled the criteria of 'talk and die' were documented, including age, mode of injury, initial GCS, lucid interval, CT scan reports, operation performed, post mortem findings and intracranial cause of death. Factors considered potentially contributory to the patients' deterioration, such as delays in CT scanning or patient transfer, coagulopathy or hypoxic episodes were also noted. The incidence of 'talk and die' patients was 2.6% (15 out of 569) overall and the annual incidence did not significantly alter over the 10-year period of the study. The small number of patients precludes inferences regarding causal relationships, although potentially preventable factors, which could have been contributory to patient deterioration, were identified.

Impact of genetic factors on outcome from brain injury

Most human phenotypic characteristics are determined by the interplay of environmental factors (whether external, or related to the internal milieu) with the unique genetic attributes of the individual. The same is true for predisposition to and outcome from most disease states, with acute brain injury being no exception. A greater understanding of this interplay is likely to allow improved risk stratification of patients, the development of new preventative and therapeutic modalities, and the possibility of 'individualizing' patient management based upon their genetic inheritance.

Genetic influences on outcome following traumatic brain injury

Several genes have been implicated as influencing the outcome following traumatic brain injury (TBI). Currently the most extensively studied gene has been APOE. APOE can influence overall and rehabilitation outcome, coma recovery, risk of posttraumatic seizures, as well as cognitive and behavioral functions following TBI. Pathologically, APOE is associated with increased amyloid deposition, amyloid angiopathy, larger intracranial hematomas and more severe contusional injury. The proposed mechanism by which APOE affects the clinicopathological consequences of TBI is multifactorial and includes amyloid deposition, disruption of cytoskeletal stability, cholinergic dysfunction, oxidative stress, neuroprotection and central nervous system plasticity in response to injury. Other putative genes have been less extensively studied and require replication of the clinical findings. The COMT and DRD2 genes may influence dopamine dependent cognitive processes such as executive/frontal lobe functions. Inflammation which is a prominent component in the pathophysiological cascade initiated by TBI, is in part is mediated by the interleukin genes, while apoptosis that occurs as a consequence of TBI may be modulated by polymorphisms of the p53 gene. The ACE gene may affect TBI outcome via mechanisms of cerebral blood flow and/or autoregulation and the CACNA1A gene may exert an influence via the calcium channel and its effect on delayed cerebral edema. Although several potential genes that may influence outcome following TBI have been identified, future investigations are needed to validate these genetic studies and identify new genes that might influence outcome following TBI.

Amyotrophic lateral sclerosis as a complex genetic disease

In complex diseases like ALS, there are multiple genetic and environmental factors all contributing to disease liability. The genetic factors causing susceptibility to developing ALS can be considered a spectrum from single genes with large effect sizes causing classical Mendelian ALS, to genes of smaller effect, producing apparently sporadic disease. We examine the statistical genetic principles that underpin this model and review what is known about ALS as a disease with complex genetics.

Cholesterol in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia and affects up to 15 million people worldwide. Although no single cause of AD has been identified, recent research has suggested that several pathogenetic factors influence risk and expression. A growing amount of evidence underscores a mechanistic link between cholesterol metabolism in the brain and the formation of amyloid plaques. Excess brain cholesterol has been associated with increased formation and deposition of amyloid-beta peptide from amyloid precursor protein. Cholesterol-lowering statins have become a focus of research in AD. Genetic polymorphisms associated with pivotal points in cholesterol metabolism in brain tissues may contribute to the risk and pathogenesis of AD. In this review, we summarise current knowledge of the role of cholesterol metabolism in the pathogenesis of AD and examine the potential of statins in the prevention and treatment of AD.

Apo E genotype not associated with intravascular coagulation in traumatic brain injury

There is considerable evidence linking both genotype and coagulopathy to vascular complications of traumatic brain injury (TBI) and other cerebral insults. The authors explored a possible connection between the apolipoprotein E (Apo E) genotype, coagulopathy and intravascular microthombosis (IMT) in TBI. The predicted association was not confirmed.

Genetic influences on outcome following acute neurological insults

PURPOSE OF REVIEW

To examine the evidence for a genetic influence on clinical outcome after a variety of acute neurologic events.

RECENT FINDINGS

Clinical outcome after brain injury is variable and cannot easily be predicted. It has been proposed that genetic polymorphisms may have an important role in determining outcome from a number of conditions, including acute neurologic events. Apolipoprotein E, an important mediator of cholesterol and lipid transport in the brain, is coded by a polymorphic gene (APOE). The APOE epsilon4 allele has been associated with unfavorable outcome after traumatic brain injury (TBI), hemorrhagic stroke and subarachnoid hemorrhage (SAH). Genes involved in other pathophysiological processes, such as cytokine genes in neuroinflammation, are now being implicated. For example interleukin-6 (IL-6) promoter polymorphisms are a risk factor for poor outcome after ischemic stroke, and may have an effect after traumatic brain injury. The emerging importance of a number of other gene polymorphisms is outlined in the review.

SUMMARY

There is evidence demonstrating the epsilon4 allele of APOE predisposes to poor outcome after TBI, hemorrhagic stroke and SAH, but not ischemic stroke. The reason for this difference is unclear but it suggests there may be differences in the key mechanisms underlying the response to different types of insult. The role of other gene polymorphisms is being increasingly explored but there is still a need for larger prospective studies looking at larger panels of gene polymorphisms.

Epilepsy after head injury

PURPOSE OF REVIEW

The purpose of this short review is to provide an update on the epidemiology of posttraumatic epilepsy, associated risk factors, data from prevention studies, and recent breakthroughs in experimental research.

RECENT FINDINGS

There is increasing evidence that neuroimaging findings, stratification by neurosurgical procedures performed, and genomic information (e.g. apolipoprotein E and haptoglobin genotypes) may provide useful predictors of the individual risk of developing posttraumatic epilepsy. While antiepileptic drug prophylaxis can be effective in protecting against acute (provoked) seizures occurring within 7 days after injury, no antiepileptic drug treatment has been found to protect against the development of posttraumatic epilepsy and therefore long-term anticonvulsant prophylaxis is not recommended. Glucocorticoid administration early after head injury also has not been found to reduce the risk of posttraumatic epilepsy. At the basic research level, there have been advances in the understanding of pathophysiological changes in posttraumatic excitatory and inhibitory synapses, and the critical period for epileptogenesis after head injury has been better defined. Finally, the development of a novel animal model, which mimicks more closely human posttraumatic epilepsy, may facilitate efforts to characterize relevant epileptogenic mechanisms and to identify clinically effective antiepileptogenic treatments.

SUMMARY

Despite the continuing lack of clinically effective agents for posttraumatic epilepsy prophylaxis, recent advances in basic and clinical research offer new hope for success in the development of new strategies for prevention and treatment.

Poststroke Dementia in the Elderly

Risk of dementia increases after stroke, and poststroke dementia (PSD) is an important cause of disability in the elderly. The prevalence rates of PSD vary from 12.2% to 31.8% within 3 months to 1 year after stroke, depending on patient populations and the diagnostic criteria used in the numerous studies. Incidence rates of PSD increase with time after the stroke. Although vascular lesions and white matter changes can explain the cognitive disorders seen in stroke patients, an underlying neurodegenerative disorder may contribute to the development of PSD. Cognitive decline may pre-date the stroke and follow a progressive course after the stroke. The vascular and degenerative processes involved share common environmental and genetic risk factors. This review explains the mechanisms of dementia in stroke patients and identifies predictive factors for PSD. The following points are successively considered: (i) demographic characteristics of the patients, including age and level of education; (ii) prestroke cognitive decline; (iii) vascular risk factors, including diabetes mellitus and prior strokes; (iv) stroke characteristics, including severity and location of the vascular lesion; (v) co-morbid disorders; and (vi) abnormalities on brain imaging, including location, size and number of vascular lesions, white matter changes and cerebral atrophy. Older age, prestroke cognitive decline, stroke recurrence, hypoxic-ischaemic disorders, left-side infarcts, strategic infarcts and white matter lesions appear to be the main predictive factors of PSD. Prevention of stroke should reduce the morbidity and mortality associated with PSD. In addition, management of PSD with secondary prevention treatments could reduce occurrence of further strokes. Cholinesterase inhibitors may be beneficial not only in Alzheimer's disease associated with cerebrovascular lesions, but also for the treatment of cholinergic dysfunction arising from pure vascular dementia. Better knowledge of the risk factors for PSD, including environmental and genetic factors, should increase the effectiveness of preventive strategies in patients with this condition.

The allelic modulation of apolipoprotein E expression by oestrogen: potential relevance for Alzheimer's disease

BACKGROUND

The epsilon4 allele of the apolipoprotein E (APOE) gene is a major genetic risk factor for Alzheimer's disease but appears to be associated with greater risk in women than in men. Some studies suggest that the level of APOE may of its own modulate the risk for Alzheimer's disease. Sex differences and an apparent benefit of oestrogen therapy suggest a role for oestrogen. APOE expression is influenced by oestrogen and oestrogen therapy may not benefit women bearing an APOE epsilon4 allele. These findings suggest an interaction between oestrogen and APOE in the Alzheimer's disease process.

AIM

To explore the hypothesis that APOE expression is regulated by a genomic mechanism and is modified by the polymorphisms in APOE associated with risk for Alzheimer's disease.

METHODS

In vitro binding studies were undertaken between oestrogen receptors and fragments of the human APOE gene. APOE gene expression was studied to investigate a possible functional interaction.

RESULTS

APOE epsilon2/epsilon3/epsilon4 coding and -219 G/T promoter polymorphisms influenced binding to the oestrogen receptor and altered transcriptional activity in response to oestrogen.

CONCLUSIONS

An allele dependent modulation of oestrogen induced regulation of APOE might be involved in the increased risk for Alzheimer's disease in women bearing an epsilon4 allele.