Polymorphisms in the brain-derived neurotrophic factor gene influence memory and processing speed one month after brain injury

Investigating the role of the brain-derived neurotrophic factor Val66Met polymorphism in repetitive mild traumatic brain injury outcomes in rats

BACKGROUND

Mild traumatic brain injury (mTBI) poses a significant public health concern, particularly regarding repetitive injury, with outcomes ranging from acute neurobehavioral deficits to long-term impairments. While demographic factors like age and sex influence outcomes, the understanding of genetic contributions, particularly the role of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism, remains limited. This study aimed to characterize acute effects of repetitive mTBI (rmTBI) in rats with the Val68Met SNP, the rodent equivalent of the human Val66Met, focusing on behavioral, fluid biomarker, and histological changes.

METHODS

Using a closed-head injury model, rats underwent five mTBIs over consecutive days. Behavioral assessments included sensorimotor function, anxiety-like behavior, spatial learning and memory, and nociceptive response. Plasma neurofilament light (NfL) levels served as a biomarker of axonal injury and immunohistochemistry evaluated microglial activation.

RESULTS

Sensorimotor deficits and increased anxiety-like behavior were found in rats with rmTBI, but these changes were not affected by sex or genotype. Plasma NfL levels were higher in rmTBI compared with sham rats, with levels greater in female rmTBI when compared with male rmTBI rats. Microglial activation was observed in the hypothalamus of injured rats, but was not influenced by genotype or sex.

CONCLUSIONS

While the Val68Met SNP did not significantly influence acute responses to rmTBI in this study, further investigation into alternative functional and pathophysiological outcomes, as well as long-term effects, is required.

Genetic Variants and Persistent Impairment Following Mild Traumatic Brain Injury: A Systematic Review

OBJECTIVE

The purpose of this review is to systematically assess primary research publications on known genetic variants, which modify the risk for symptoms or dysfunction persisting 30 days or more following mild traumatic brain injury (mTBI).

SUMMARY OF REVIEW

A search of PubMed and Embase from inception through June 2022 identified 42 studies that associated genetic variants with the presence of symptoms or cognitive dysfunction 30 days or more following mTBI. Risk of bias was assessed for each publication using the Newcastle Ottawa Scale (NOS). Fifteen of the 22 studies evaluating apolipoprotein E ( APOE ) ɛ4 concluded that it was associated with worse outcomes and 4 of the 8 studies investigating the brain-derived neurotrophic factor ( BDNF ) reported the Val66Met allele was associated with poorer outcomes. The review also identified 12 studies associating 28 additional variants with mTBI outcomes. Of these, 8 references associated specific variants with poorer outcomes. Aside from analyses comparing carriers and noncarriers of APOE ɛ4 and BDNF Val66Met, most of the reviewed studies were too dissimilar, particularly in terms of specific outcome measures but also in genes examined, to allow for direct comparisons of their findings. Moreover, these investigations were observational and subject to varying degrees of bias.

CONCLUSIONS

The most consistent finding across articles was that APOE ɛ4 is associated with persistent post-mTBI impairment (symptoms or cognitive dysfunction) more than 30 days after mTBI. The sparsity of other well-established and consistent findings in the mTBI literature should motivate larger, prospective studies, which characterize the risk for persistent impairment with standardized outcomes in mTBI posed by other genetic variants influencing mTBI recovery.

BDNF: New Views of an Old Player in Traumatic Brain Injury

Traumatic brain injury is a common health problem affecting millions of people each year. BDNF has been investigated in the context of traumatic brain injury due to its crucial role in maintaining brain homeostasis. Val66Met is a functional single-nucleotide polymorphism that results in a valine-to-methionine amino acid substitution at codon 66 in the BDNF prodomain, which ultimately reduces secretion of BDNF. Here, we review experimental animal models as well as clinical studies investigating the role of the Val66Met single-nucleotide polymorphism in traumatic brain injury outcomes, including cognitive function, motor function, neuropsychiatric symptoms, and nociception. We also review studies investigating the role of BDNF on traumatic brain injury pathophysiology as well as circulating BDNF as a biomarker of traumatic brain injury.

A pilot study examining BDNF Val66Met polymorphism and biological sex: Relationships with baseline cognitive functioning in adolescent athletes

The purpose of this exploratory study was to examine interactive relationships between a common brain-derived neurotrophic factor (BDNF) polymorphism (Val66Met) and biological sex on cognitive functioning in a sample of healthy adolescent athletes. Participants included 82 student athletes (age: M = 12.85 years, SD = 1.13) who were involved in a clinically-based sports-concussion management program. Athletes completed the ImPACT computerized battery at baseline and provided buccal samples for determination of their BDNF genotype. Two-way ANOVAs were used to evaluate the effect of BDNF genotype (Met+ vs. Met-) and sex (male vs. female) on cognitive functioning (subgroup n's: Female/Met+ = 12, Female/Met- = 26, Male/Met+ = 12, Male/Met- = 32). ANOVAs revealed non-significant main effects for both BDNF genotype and sex across all four cognitive composites. However, there was a significant BDNF genotype by sex interaction for the visual-motor speed composite (p = .015; ηp2 = .073), such that female Met carriers demonstrated better performance than male Met carriers. In contrast, no differences were found on visual-motor speed performance between females and males without a Met allele. Although these results will need to be replicated using larger samples, our preliminary findings lend support to the view that the Met allele may be somewhat neuroprotective in healthy adolescent females.

[Risk factors for cancer-related cognitive impairment in breast and colorectal cancer patients who undergo chemotherapy]

BACKGROUND

Our study aims to evaluate the impact of different factors on cancer-related cognitive impairment in patients who undergo chemotherapy.

METHODOLOGY

Prospective longitudinal single-centre study that included patients with breast and colon carcinoma who underwent chemotherapy as part of their treatment. Clinical and genetic characteristics of the patients (single nucleotide polymorphisms, SNPs) were collected. Patients' neurocognitive status was assessed using eleven validated tests at three time points: before chemotherapy (M0 - baseline), between one and four weeks after completing chemotherapy (M1), and between 24-30 weeks after completing chemotherapy (M2).

RESULTS

Sixty-two patients were included in this study; 82% were female, median age was 56 years (range 30-74), and 64.5% had been diagnosed with breast cancer. Overall, better cognitive results at M0 were associated with age < 55 years, higher educational level, absence of comorbidities, and the CC variant rs471692 (TOP2A). Significant decline was found between M0 to M1 in the Rey Auditory Verbal Learning Test and the Letter and Number test, with evidence of recovery in M2 compared to M0 regarding the following test: Visual Memory, Functioning Assessment Short Test (FAST), Digit Symbol Substitution and Cube. In the multivariate analysis, being =55 years of age, adjuvant chemotherapy, presence of comorbidities, tobacco and alcohol use, and GT variant rs1800795 were associated with cognitive decline between M0 and M1.

CONCLUSION

Being =55 years of age, female, presence of comorbidities and basic education level are related to a higher risk of cognitive impairment after chemotherapy.

COMT Val158Met and BDNF Val66Met Single-Nucleotide Polymorphisms Are Not Associated With Emotional Distress One Year After Moderate-Severe Traumatic Brain Injury

Emotional distress is a common, but poorly addressed, feature of moderate-severe traumatic brain injury (TBI). Previously identified sociodemographic, psychological, and injury-related factors account for only a small proportion of the variability in emotional distress post-TBI. Genetic factors may help to further understand emotional distress in this population. The catechol-O-methyltransferase (COMT) Val158 and brain-derived neurotrophic factor (BDNF) 66Met single-nucleotide polymorphisms (SNPs) have been identified as possible contributory factors to outcomes after TBI. We investigated whether the COMT Val158 and BDNF 66Met SNPs were associated with emotional distress 1 year after moderate-severe TBI, and whether these associations were moderated by age, sex, and TBI severity (as measured by the duration of post-traumatic amnesia [PTA]). Moderate-severe TBI survivors (COMT, n = 391; BDNF, n = 311) provided saliva samples after admission to a TBI rehabilitation hospital. At a follow-up interview ∼1 year after injury, participants completed a self-report measure of emotional distress (Hospital Anxiety and Depression Scale; HADS). Multiple linear regression models were constructed for each SNP to predict total scores on the HADS. Neither COMT Val158 nor BDNF 66Met carriage status (carrier vs. non-carrier) significantly predicted emotional distress (COMT, p = 0.49; BDNF, p = 0.66). Interactions of SNP × age (COMT, p = 0.90; BDNF, p = 0.93), SNP × sex (COMT, p = 0.09; BDNF, p = 0.60), SNP × injury severity (COMT, p = 0.53; BDNF, p = 0.87), and SNP × sex × age (COMT, p = 0.08; BDNF, p = 0.76) were also non-significant. Our null findings suggest that COMT Val158 and BDNF 66Met SNPs do not aid the prediction of emotional distress 1 year after moderate-severe TBI, neither in isolation nor in interaction with age, sex and injury severity. The reporting of null findings such as ours is important to avoid publication bias and prompt researchers to consider the challenges of single-gene candidate studies in understanding post-TBI outcomes. Analyses in larger samples that incorporate multiple genetic factors and their relevant moderating factors may provide a greater understanding of the role of genetics in post-TBI emotional distress.

APOE & BDNF polymorphisms interact to affect memory performance at baseline in adolescent athletes

Although several single-nucleotide polymorphisms have been associated with cognitive functioning in a variety of healthy and clinical samples, the influence of gene × gene interactions on cognition is poorly understood. The purpose of this study was to examine interactive relationships between apolipoprotein E (APOE) and brain-derived neurotrophic factor (BDNF) polymorphisms on cognitive functioning in a sample of healthy adolescent athletes. Participants of this cross-sectional study included 78 student-athletes (52.6% male; age: M = 13.31, SD = 1.23). Athletes completed the Immediate Post-Concussion and Cognitive Testing (ImPACT) computerized battery at baseline. APOE and BDNF genotypes were determined with buccal samples (APOE ε4+: n = 26; APOE ε4-: n = 52; BDNF Met+: n = 23; BDNF Met-: n = 55). Two-way analyses of variance (ANOVAs) were used to evaluate the associations among APOE (ε4+ vs. ε4-) and BDNF (Met+ vs. Met-) genotypes and the ImPACT cognitive composites and two-factor model. No main effects were observed for either APOE or BDNF genotypes across the cognitive outcomes. However, there was a significant APOE × BDNF genotype interaction for the verbal (p=.009, η_p²=.091) and visual (p = .012, η_p²=.082) memory composites and the memory factor (p = .001, η_p²=.133), such that ε4+/Met+ carriers demonstrated poorer performance relative to other allele combinations. No significant interactions were observed for the visual motor speed (p = .263, η_p²=.017) or reaction time (p = .825, η_p²=.001) composites or the speed factor (p = .205, η_p²=.022). Our findings suggest an important relationship between APOE and BDNF genotypes on verbal and visual memory performance in healthy adolescent athletes. Clinicians may use this information to offer individualized concussion management based on individual athlete characteristics related to genetics and cognition.

Interactive effects of the BDNF Val66Met polymorphism and posttraumatic stress disorder on cognition in U.S. military veterans

Posttraumatic stress disorder (PTSD) is associated with mild-to-moderate deficits in cognition. The Met allele of the brain-derived neurotrophic factor (BDNF) Val66Met gene may also be associated with deficits in cognition. However, findings are inconsistent and may be sensitive to moderating variables such as psychopathology. While emerging research suggests that PTSD and the Met allele may interact, few studies have replicated this effect or examined the interactive effect of PTSD and the Met allele on subjective cognition. To address this gap, the current study analyzed data from European-American (EA) U.S. military veterans (n = 1244) who participated in the National Health and Resilience in Veterans Study (NHRVS) to examine the main and interactive effects of BDNF Val66Met genotype and probable PTSD on objective and subjective cognition. Results revealed significant (p's < 0.001) interactions between Met allele carrier status and probable PTSD in objective and subjective cognition. Among individuals with probable PTSD (n = 131), the Met allele was associated with poorer objective (p < .001, d = 0.62) and subjective cognition (p = .001, d = 0.53). Among individuals without PTSD (n = 1113), the Met allele was not significantly associated with objective or subjective cognition. These findings suggest that PTSD may moderate the association between Met allele carrier status and cognition. Implications of these results for the mitigation of cognitive dysfunction in older veterans are discussed.

Integrative Neuroinformatics for Precision Prognostication and Personalized Therapeutics in Moderate and Severe Traumatic Brain Injury

Despite changes in guideline-based management of moderate/severe traumatic brain injury (TBI) over the preceding decades, little impact on mortality and morbidity have been seen. This argues against the "one-treatment fits all" approach to such management strategies. With this, some preliminary advances in the area of personalized medicine in TBI care have displayed promising results. However, to continue transitioning toward individually-tailored care, we require integration of complex "-omics" data sets. The past few decades have seen dramatic increases in the volume of complex multi-modal data in moderate and severe TBI care. Such data includes serial high-fidelity multi-modal characterization of the cerebral physiome, serum/cerebrospinal fluid proteomics, admission genetic profiles, and serial advanced neuroimaging modalities. Integrating these complex and serially obtained data sets, with patient baseline demographics, treatment information and clinical outcomes over time, can be a daunting task for the treating clinician. Within this review, we highlight the current status of such multi-modal omics data sets in moderate/severe TBI, current limitations to the utilization of such data, and a potential path forward through employing integrative neuroinformatic approaches, which are applied in other neuropathologies. Such advances are positioned to facilitate the transition to precision prognostication and inform a top-down approach to the development of personalized therapeutics in moderate/severe TBI.

Moderators of gene-outcome associations following traumatic brain injury

The field of genomics is the principal avenue in the ongoing development of precision/personalised medicine for a variety of health conditions. However, relating genes to outcomes is notoriously complex, especially when considering that other variables can change, or moderate, gene-outcome associations. Here, we comprehensively discuss moderation of gene-outcome associations in the context of traumatic brain injury (TBI), a common, chronically debilitating, and costly neurological condition that is under complex polygenic influence. We focus our narrative review on single nucleotide polymorphisms (SNPs) of three of the most studied genes (apolipoprotein E, brain-derived neurotrophic factor, and catechol-O-methyltransferase) and on three demographic variables believed to moderate associations between these SNPs and TBI outcomes (age, biological sex, and ethnicity). We speculate on the mechanisms which may underlie these moderating effects, drawing widely from biomolecular and behavioural research (n = 175 scientific reports) within the TBI population (n = 72) and other neurological, healthy, ageing, and psychiatric populations (n = 103). We conclude with methodological recommendations for improved exploration of moderators in future genetics research in TBI and other populations.

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.

The Role of BDNF in Experimental and Clinical Traumatic Brain Injury

Traumatic brain injury is one of the leading causes of mortality and morbidity in the world with no current pharmacological treatment. The role of BDNF in neural repair and regeneration is well established and has also been the focus of TBI research. Here, we review experimental animal models assessing BDNF expression following injury as well as clinical studies in humans including the role of BDNF polymorphism in TBI. There is a large heterogeneity in experimental setups and hence the results with different regional and temporal changes in BDNF expression. Several studies have also assessed different interventions to affect the BDNF expression following injury. Clinical studies highlight the importance of BDNF polymorphism in the outcome and indicate a protective role of BDNF polymorphism following injury. Considering the possibility of affecting the BDNF pathway with available substances, we discuss future studies using transgenic mice as well as iPSC in order to understand the underlying mechanism of BDNF polymorphism in TBI and develop a possible pharmacological treatment.

Genetic Variation and Impact on Outcome in Traumatic Brain Injury: an Overview of Recent Discoveries

PURPOSE OF REVIEW

Traumatic brain injury (TBI) has a significant burden of disease worldwide and outcomes vary widely. Current prognostic tools fail to fully account for this variability despite incorporating clinical, radiographic, and biochemical data. This variance could possibly be explained by genotypic differences in the patient population. In this review, we explore single nucleotide polymorphism (SNP) TBI outcome association studies.

RECENT FINDINGS

In recent years, SNP association studies in TBI have focused on global, neurocognitive/neuropsychiatric, and physiologic outcomes. While the APOE gene has been the most extensively studied, other genes associated with neural repair, cell death, the blood-brain barrier, cerebral edema, neurotransmitters, mitochondria, and inflammatory cytokines have all been examined for their association with various outcomes following TBI. The results have been mixed across studies and even within genes. SNP association studies provide insight into mechanisms by which outcomes may vary following TBI. Their individual clinical utility, however, is often limited by small sample sizes and poor reproducibility. In the future, they may serve as hypothesis generating for future therapeutic targets.

Brain-Derived Neurotrophic Factor Polymorphism Influences Response to Single-Pulse Transcranial Magnetic Stimulation at Rest

OBJECTIVES

The ability of noninvasive brain stimulation to modulate corticospinal excitability and plasticity is influenced by genetic predilections such as the coding for brain-derived neurotrophic factor (BDNF). Otherwise healthy individuals presenting with BDNF Val66Met (Val/Met) polymorphism are less susceptible to changes in excitability in response to repetitive transcranial magnetic stimulation (TMS) and paired associative stimulation paradigms, reflecting reduced neuroplasticity, compared to Val homozygotes (Val/Val). In the current study, we investigated whether BDNF polymorphism influences "baseline" excitability under TMS conditions that are not repetitive or plasticity-inducing. Cross-sectional BDNF levels could predict TMS response more generally because of the ongoing plasticity processes.

MATERIALS AND METHODS

Forty-five healthy individuals (23 females; age: 25.3 ± 7.0 years) participated in the study, comprising two groups. Motor evoked potentials (MEP) were collected using single-pulse TMS paradigms at fixed stimulation intensities at 110% of the resting motor threshold in one group, and individually-derived intensities based on MEP sizes of 1 mV in the second group. Functional variant Val66Met (rs6265) was genotyped from saliva samples by a technician blinded to the identity of DNA samples.

RESULTS

Twenty-seven participants (60.0%) were identified with Val/Val, sixteen (35.5%) with Val/Met genotype, and two with Met/Met genotype. MEP amplitudes were significantly diminished in the Val/Met than Val/Val individuals. These results held independent of the single-pulse TMS paradigm of choice (p = 0.017110% group; p = 0.035 1 mV group), age, and scalp-to-coil distances.

CONCLUSIONS

The findings should be further substantiated in larger-scale studies. If validated, intrinsic differences by BDNF polymorphism status could index response to TMS prior to implementing plasticity-inducing protocols.

Dissociation of BDNF Val66Met polymorphism on neurocognitive functioning in military veterans with and without a history of remote mild traumatic brain injury

OBJECTIVE

Since neurocognitive functioning following mild traumatic brain injury (mTBI) may be influenced by genetic factors that mediate synaptic survival and repair, we examined the influence of a common brain-derived neurotrophic factor (BDNF) polymorphism (Val66Met) on cognition using a well-defined sample of military Veterans with and without a history of mTBI.

METHOD

Participants included 138 Veterans (mTBI = 75; military controls [MCs] = 63) who underwent neuropsychological testing, including completion of self-report measures assessing psychiatric distress, and BDNF genotyping. The mTBI group was tested roughly 66.7 months following their most recent mTBI. Veterans were divided into two groups-Met+ (Met/Met and Met/Val; n = 49) and Met- (Val/Val; n = 89) and compared on domain-specific cognitive composite scores representing memory, executive functioning, and visuospatial speed.

RESULTS

ANCOVAs adjusting for psychiatric distress, sex, years of education, and ethnicity/race revealed a significant group (mTBI vs. MC) by BDNF genotype (Met + vs. Met-) interaction for the memory (p = .024; η_p ² = .039) and executive functioning (p = .010; η_p ² = .050) composites, such that Met+ mTBI Veterans demonstrated better performance than Met- mTBI Veterans on the cognitive measures, whereas Met+ MCs demonstrated worse performance relative to Met- MCs on the cognitive measures. No significant interaction was observed for the visuospatial speed composite (p = .938; η_p ² < .001).

CONCLUSIONS

These findings offer preliminary evidence to suggest that the Met allele may be protective in the context of remote mTBI. Findings need to be replicated using larger samples, and future studies are necessary to elucidate the precise mechanisms and neural underpinnings of this interaction.

Genetic drivers of cerebral blood flow dysfunction in TBI: a speculative synthesis

Cerebral autoregulatory dysfunction after traumatic brain injury (TBI) is strongly linked to poor global outcome in patients at 6 months after injury. However, our understanding of the drivers of this dysfunction is limited. Genetic variation among individuals within a population gives rise to single-nucleotide polymorphisms (SNPs) that have the potential to influence a given patient's cerebrovascular response to an injury. Associations have been reported between a variety of genetic polymorphisms and global outcome in patients with TBI, but few studies have explored the association between genetic variants and cerebrovascular function after injury. In this Review, we explore polymorphisms that might play an important part in cerebral autoregulatory capacity after TBI. We outline a variety of SNPs, their biological substrates and their potential role in mediating cerebrovascular reactivity. A number of candidate polymorphisms exist in genes that are involved in myogenic, endothelial, metabolic and neurogenic vascular responses to injury. Furthermore, polymorphisms in genes involved in inflammation, the central autonomic response and cortical spreading depression might drive cerebrovascular reactivity. Identification of candidate genes involved in cerebral autoregulation after TBI provides a platform and rationale for further prospective investigation of the link between genetic polymorphisms and autoregulatory function.

Genetic Background Influences Acute Response to TBI in Kindling-Susceptible, Kindling-Resistant, and Outbred Rats

We hypothesized that the acute response to traumatic brain injury (TBI) shares mechanisms with brain plasticity in the kindling model. Utilizing two unique, complementary strains of inbred rats, selected to be either susceptible or resistant to seizure-induced plasticity evoked by kindling of the perforant path, we examined acute electrophysiological alterations and differences in brain-derived neurotrophic factor (BDNF) protein concentrations after a moderate-to-severe brain injury. At baseline, limited strain-dependent differences in acute electrophysiological activity were found, and no differences in BDNF. Following injury, pronounced strain-dependent differences in electrophysiologic activity were noted at 0.5 min. However, the divergence is transient, with diminished differences at 5 min after injury and no differences at 10 and 15 min after injury. Strain-specific differences in BDNF protein concentration were noted 4 h after injury. A simple risk score model generated by machine learning and based solely on post-injury electrophysiologic activity at the 0.5-min timepoint distinguished perforant path kindling susceptible (PPKS) rats from non-plasticity-susceptible strains. The findings demonstrate that genetic background which affects brain circuit plasticity also affects acute response to TBI. An improved understanding of the effect of genetic background on the cellular, molecular, and circuit plasticity mechanisms activated in response to TBI and their timecourse is key in developing much-needed novel therapeutic approaches.

BDNF Val66Met Positive Players Demonstrate Diffusion Tensor Imaging Consistent With Impaired Myelination Associated With High Levels of Soccer Heading: Indication of a Potential Gene-Environment Interaction Mechanism

The purpose of this study was to examine the potential effect modifying role of the BDNF Val66Met polymorphism on the association of soccer heading with white matter microstructure. We studied 312 players enrolled in the ongoing Einstein Soccer Study, a longitudinal study of amateur soccer player in New York City and surrounding areas. At enrollment and 2 years later, total heading in the prior 12 months (12-mo.) was estimated using an established self-report instrument and diffusion tensor imaging (DTI) was performed. Generalized Estimating Equations (GEE) logistic regression models were employed to test effect modification by the BDNF Val66Met polymorphism on the association between 12-mo. heading exposure and DTI. We identified a significant interaction of 12-mo heading*BDNF Val66Met genotype on the presence of low Radial Diffusivity, a DTI marker associated with myelination. Only Met (+) players demonstrated significantly reduced odds of low RD [OR (95 % CI): -2.36 (-3.53, -1.19)] associated with the highest vs. lowest quartile of 12-mo heading exposure. BDNF Val66Met (+) soccer players with long-term exposure to high levels of heading exhibit less low Radial Diffusivity, suggesting impaired re-myelination may be a substrate of the previously reported association between heading and poor functional outcomes in soccer players.

BDNF Val66Met Genetic Polymorphism Results in Poor Recovery Following Repeated Mild Traumatic Brain Injury in a Mouse Model and Treatment With AAV-BDNF Improves Outcomes

Clinicians have long noticed that some Traumatic Brain Injury (TBI) patients have worse symptoms and take a longer time to recover than others, for reasons unexplained by known factors. Identifying what makes some individuals more susceptible is critical to understanding the underlying mechanisms through which TBI causes deleterious effects. We have sought to determine the effect of a single nucleotide polymorphism (SNP) in Brain-derived neurotrophic factor (BDNF) at amino acid 66 (rs6265) on recovery after TBI. There is controversy from human studies as to whether the BDNF Val66Val or Val66Met allele is the risk factor for worse outcomes after brain trauma. We therefore investigated cellular and behavioral outcomes in genetically engineered mice following repeated mild TBI (rmTBI) using a lateral fluid percussion (LFP) injury model. We found that relative to injured Val66Val carriers, injured Val66Met carriers had a larger inflammation volume and increased levels of neurodegeneration, apoptosis, p-tau, activated microglia, and gliosis in the cortex and/or hippocampus at 1 and/or 21 days post-injury (DPI). We therefore concluded that the Val66Met genetic polymorphism is a risk factor for poor outcomes after rmTBI. In order to determine the mechanism for these differences, we investigated levels of the apoptotic-inducing pro BDNF and survival-inducing mature BDNF isoforms and found that Met carriers had less total BDNF in the cortex and a higher pro/mature ratio of BDNF in the hippocampus. We then developed a personalized approach to treating genetically susceptible individuals by overexpressing wildtype BDNF in injured Val66Met mice using an AAV-BDNF virus. This intervention improved cellular, motor, and cognitive behavior outcomes at 21 DPI and increased levels of mature BDNF and phosphorylation of mature BDNF's receptor trkB. This study lays the groundwork for further investigation into the genetics that play a role in the extent of injury after rmTBI and highlights how personalized therapeutics may be targeted for recovery in susceptible individuals.

Blast-Related Traumatic Brain Injury: Current Concepts and Research Considerations

Traumatic brain injury (TBI) is a well-known consequence of participation in activities such as military combat or collision sports. But the wide variability in eliciting circumstances and injury severities makes the study of TBI as a uniform disease state impossible. Military Service members are under additional, unique threats such as exposure to explosive blast and its unique effects on the body. This review is aimed toward TBI researchers, as it covers important concepts and considerations for studying blast-induced head trauma. These include the comparability of blast-induced head trauma to other mechanisms of TBI, whether blast overpressure induces measureable biomarkers, and whether a biodosimeter can link blast exposure to health outcomes, using acute radiation exposure as a corollary. This examination is contextualized by the understanding of concussive events and their psychological effects throughout the past century's wars, as well as the variables that predict sustaining a TBI and those that precipitate or exacerbate psychological conditions. Disclaimer: The views expressed in this article are solely the views of the authors and not those of the Department of Defense Blast Injury Research Coordinating Office, US Army Medical Research and Development Command, US Army Futures Command, US Army, or the Department of Defense.

The Influence of the Val66Met Polymorphism of Brain-Derived Neurotrophic Factor on Neurological Function after Traumatic Brain Injury

Functional outcomes after traumatic brain injury (TBI) vary widely across patients with apparently similar injuries. This variability hinders prognosis, therapy, and clinical innovation. Recently, single nucleotide polymorphism (SNPs) that influence outcome after TBI have been identified. These discoveries create opportunities to personalize therapy and stratify clinical trials. Both of these changes would propel clinical innovation in the field. This review focuses on one of most well-characterized of these SNPs, the Val66Met SNP in the brain-derived neurotrophic factor (BDNF) gene. This SNP influences neurological function in healthy subjects as well as TBI patients and patients with similar acute insults to the central nervous system. A host of other patient-specific factors including ethnicity, age, gender, injury severity, and post-injury time point modulate this influence. These interactions confound efforts to define a simple relationship between this SNP and TBI outcomes. The opportunities and challenges associated with personalizing TBI therapy around this SNP and other similar SNPs are discussed in light of these results.

Genetic Influences on Patient-Oriented Outcomes in Traumatic Brain Injury: A Living Systematic Review of Non-Apolipoprotein E Single-Nucleotide Polymorphisms

There is a growing literature on the impact of genetic variation on outcome in traumatic brain injury (TBI). Whereas a substantial proportion of these publications have focused on the apolipoprotein E (APOE) gene, several have explored the influence of other polymorphisms. We undertook a systematic review of the impact of single-nucleotide polymorphisms (SNPs) in non–apolipoprotein E (non-APOE) genes associated with patient outcomes in adult TBI). We searched EMBASE, MEDLINE, CINAHL, and gray literature from inception to the beginning of August 2017 for studies of genetic variance in relation to patient outcomes in adult TBI. Sixty-eight articles were deemed eligible for inclusion into the systematic review. The SNPs described were in the following categories: neurotransmitter (NT) in 23, cytokine in nine, brain-derived neurotrophic factor (BDNF) in 12, mitochondrial genes in three, and miscellaneous SNPs in 21. All studies were based on small patient cohorts and suffered from potential bias. A range of SNPs associated with genes coding for monoamine NTs, BDNF, cytokines, and mitochondrial proteins have been reported to be associated with variation in global, neuropsychiatric, and behavioral outcomes. An analysis of the tissue, cellular, and subcellular location of the genes that harbored the SNPs studied showed that they could be clustered into blood–brain barrier associated, neuroprotective/regulatory, and neuropsychiatric/degenerative groups. Several small studies report that various NT, cytokine, and BDNF-related SNPs are associated with variations in global outcome at 6–12 months post-TBI. The association of these SNPs with neuropsychiatric and behavioral outcomes is less clear. A definitive assessment of role and effect size of genetic variation in these genes on outcome remains uncertain, but could be clarified by an adequately powered genome-wide association study with appropriate recording of outcomes.

Genetic factors associated with the predisposition to late onset Alzheimer's disease

BACKGROUND

Alzheimer's disease is a progressive, irreversible neurodegenerative disorder characterized by loss of memory and cognitive skills. More than 90% of cases are sporadic and have later age of onset. Many studies have shown a genetic predisposition for late onset Alzheimer's disease (LOAD). The most studied genetic predisposition factor is apolipoprotein E gene besides other susceptibility genes involved in vascular pathologies, homocysteine metabolism, and neuronal growth and differentiation such as methylenetetrahydrofolate reductase (MTHFR), angiotensin-converting enzyme (ACE), APOB and brain derived neurotrophic factor (BDNF).

METHODS

In this study Factor V Leiden (G1691A) and H1299R, prothrombin G20210A, Factor XIII V34L, B-fibrinogen -455G>A, PAI-1 5G/4G, HPA1 b/a, MTHFR C677T, MTHFR A1298C, APOE, ACE I/D, BDNF C270T and G196A polymorphisms were evaluated in 100 LOAD patients and 100 age matched healthy controls.

RESULTS

APOE4 allele, MTHFR CC^A1298C and BDNF TT^C270T genotypes were significantly higher in LOAD patients compared to the control group (p < 0.001, p = 0.04, p = 0.03, respectively). There were no significant associations between other genotypes and allele frequencies. Mini-Mental State Examination (MMSE) scores and age at onset of the patients were also evaluated for each and combined genotypes. Age at onset was significantly lowered by about approximately 4 and 5 years in patients carrying BDNF TT^C270T and MTHFR TT^C677T genotypes, respectively.

CONCLUSION

APOE, MTHFR A1298C and BDNF C270T polymorphisms may be associated with LOAD and BDNF and MTHFR alleles may play a role in the age at onset of the LOAD.

The neurobiological effects of repetitive head impacts in collision sports

It is now recognized that repetitive head impacts (RHI) in sport have the potential for long-term neurological impairments. In order to identify targets for intervention and/or pharmacological treatment, it is necessary to characterize the neurobiological mechanisms associated with RHI. This review aims to summarize animal and human studies that specifically address Blood Brain Barrier (BBB) dysfunction, abnormal neuro-metabolic and neuro-inflammatory processes as well as Tau aggregation associated with RHI in collision sports. Additionally, we examine the influence of physical activity and genetics on outcomes of RHI, discuss methodological considerations, and provide suggestions for future directions of this burgeoning area of research.

Impact of brain-derived neurotrophic factor genetic polymorphism on cognition: A systematic review

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) has an important role in the neurogenesis and neuroplasticity of the brain. This systematic review was designed to examine the association between BDNF Val66Met (rs6265) polymorphism and four cognitive domains-attention and concentration, executive function, verbal fluency, and memory, respectively.

METHODOLOGY

Primary literature search was performed using search engines such as PubMed and Scopus. Observational studies that evaluated the neurocognitive performances in relation to BDNF polymorphism within human subjects were included in this review, while animal studies, overlapping studies, and meta-analysis were excluded.

RESULTS

Forty of 82 reviewed studies (48.8%) reported an association between Val66Met polymorphism and neurocognitive domains. The proportion of the studies showing positive findings in cognitive performances between Val/Val homozygotes and Met carriers was comparable, at 30.5% and 18.3%, respectively. The highest percentage of positive association between Val66Met polymorphism and neurocognition was reported under the memory domain, with 26 of 63 studies (41.3%), followed by 18 of 47 studies (38.3%) under the executive function domain and four of 23 studies (17.4%) under the attention and concentration domain. There were no studies showing an association between Val66Met polymorphism and verbal fluency. In particular, Val/Val homozygotes performed better in tasks related to the memory domain, while Met carriers performed better in terms of executive function, in both healthy individuals and clinical populations.

CONCLUSION

While numerous studies report an association between Val66Met polymorphism and neurocognitive changes in executive function and memory domains, the effect of Met allele has not been clearly established.

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.

Copolymer-1 enhances cognitive performance in young adult rats

Cognitive impairment is a dysfunction observed as a sequel of various neurodegenerative diseases, as well as a concomitant element in the elderly stages of life. In clinical settings, this malfunction is identified as mild cognitive impairment. Previous studies have suggested that cognitive impairment could be the result of a reduction in the expression of brain-derived neurotrophic factor (BDNF) and/or immune dysfunction. Copolymer-1 (Cop-1) is an FDA-approved synthetic peptide capable of inducing the activation of Th2/3 cells, which are able to release BDNF, as well as to migrate and accumulate in the brain. In this study, we evaluated the effect of Cop-1 immunization on improvement of cognition in adult rats. For this purpose, we performed four experiments. We evaluated the effect of Cop-1 immunization on learning/memory using the Morris water maze for spatial memory and autoshaping for associative memory in 3- or 6-month-old rats. BDNF concentrations at the hippocampus were determined by ELISA. Cop-1 immunization induced a significant improvement of spatial memory and associative memory in 6-month-old rats. Likewise, Cop-1 improved spatial memory and associative memory when animals were immunized at 3 months and evaluated at 6 months old. Additionally, Cop-1 induced a significant increase in BDNF levels at the hippocampus. To our knowledge, the present investigation reports the first instance of Cop-1 treatment enhancing cognitive function in normal young adult rats, suggesting that Cop-1 may be a practical therapeutic strategy potentially useful for age- or disease-related cognitive impairment.

The association between BDNF Val66Met polymorphism and emotional symptoms after mild traumatic brain injury

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is one of the most abundant neurotrophins in the adult brain, and it plays important roles in modulating synaptic plasticity and synaptogenesis. This study attempted to elucidate the role of the BDNF variant rs6265 in emotional symptoms following mild traumatic brain injury (mTBI).

METHODS

To investigate the association between BDNF Val66Met polymorphism (rs6265) and emotional symptoms in mTBI patients, we recruited 192 mTBI patients and evaluated their Beck Anxiety Inventory (BAI) and Beck Depression Inventory (BDI) scores in the first and sixth week after mTBI.

RESULTS

The patients carrying the T allele of rs6265 had significantly higher BAI scores in the first week following mTBI. In addition, the patients carrying the T allele also showed higher scores of BDI in the first week. In the gender-specific subgroup analysis, the male patients carrying the T allele of rs6265 had higher scores of both BAI and BDI in the first and sixth week. Meanwhile, female patients carrying the T allele also had significantly higher scores of BDI in the first week following mTBI.

CONCLUSIONS

This study provides evidence for the association between the BDNF variant rs6265 and emotional symptoms following mTBI.

BDNF genotype is associated with hippocampal volume in mild traumatic brain injury

The negative long-term effects of mild traumatic brain injury (mTBI) have been a growing concern in recent years, with accumulating evidence suggesting that mTBI combined with additional vulnerability factors may induce neurodegenerative-type changes in the brain. However, the factors instantiating risk for neurodegenerative disease following mTBI are unknown. This study examined the link between mTBI and brain-derived neurotrophic factor (BDNF) genotype, which has previously been shown to regulate processes involved in neurodegeneration including synaptic plasticity and facilitation of neural survival through its expression. Specifically, we examined nine BDNF single-nucleotide polymorphisms (SNPs; rs908867, rs11030094, rs6265, rs10501087, rs1157659, rs1491850, rs11030107, rs7127507 and rs12273363) previously associated with brain atrophy or memory deficits in mTBI. Participants were 165 white, non-Hispanic Iraq and Afghanistan war veterans between the ages of 19 and 58, 110 of whom had at least one mTBI in their lifetime. Results showed that the BDNF SNP rs1157659 interacted with mTBI to predict hippocampal volume. Furthermore, exploratory analysis of functional resting state data showed that rs1157659 minor allele homozygotes with a history of mTBI had reduced functional connectivity in the default mode network compared to major allele homozygotes and heterozygotes. Apolipoprotein E (APOE) was not a significant predictor of hippocampal volume or functional connectivity. These results suggest that rs1157659 minor allele homozygotes may be at greater risk for neurodegeneration after exposure to mTBI and provide further evidence for a potential role for BDNF in regulating neural processes following mTBI.

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.

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.

Pathological vascular and inflammatory biomarkers of acute- and chronic-phase traumatic brain injury

Given the demand for developing objective methods for characterizing traumatic brain injury (TBI), research dedicated to evaluating putative biomarkers has burgeoned over the past decade. Since it is critical to elucidate the underlying pathological processes that underlie the higher diverse outcomes that follow neurotrauma, considerable efforts have been aimed at identifying biomarkers of both the acute- and chronic-phase TBI. Such information is not only critical for helping to elucidate the pathological changes that lead to poor long-term outcomes following TBI but it may also assist in the identification of possible prevention and interventions for individuals who sustain head trauma. In the current review, we discuss the potential role of vascular dysfunction and chronic inflammation in both acute- and chronic-phase TBI, and we also highlight existing studies that have investigated inflammation biomarkers associated with poorer injury outcome.

Behavioral and inflammatory response in animals exposed to a low-pressure blast wave and supplemented with β-alanine

This study investigated the benefit of β-alanine (BA) supplementation on behavioral and cognitive responses relating to mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD) in rats exposed to a low-pressure blast wave. Animals were fed a normal diet with or without (PL) BA supplementation (100 mg kg⁻¹) for 30-day, prior to being exposed to a low-pressure blast wave. A third group of animals served as a control (CTL). These animals were fed a normal diet, but were not exposed to the blast. Validated cognitive-behavioral paradigms were used to assess both mTBI and PTSD-like behavior on days 7–14 following the blast. Brain-derived neurotrophic factor (BDNF), neuropeptide Y, glial fibrillary acidic protein (GFAP) and tau protein expressions were analyzed a day later. In addition, brain carnosine and histidine content was assessed as well. The prevalence of animals exhibiting mTBI-like behavior was significantly lower (p = 0.044) in BA than PL (26.5 and 46%, respectively), but no difference (p = 0.930) was noted in PTSD-like behavior between the groups (10.2 and 12.0%, respectively). Carnosine content in the cerebral cortex was higher (p = 0.048) for BA compared to PL, while a trend towards a difference was seen in the hippocampus (p = 0.058) and amygdala (p = 0.061). BDNF expression in the CA1 subregion of PL was lower than BA (p = 0.009) and CTL (p < 0.001), while GFAP expression in CA1 (p = 0.003) and CA3 (p = 0.040) subregions were higher in PL than other groups. Results indicated that BA supplementation for 30-day increased resiliency to mTBI in animals exposed to a low-pressure blast wave.

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.

Post-concussion symptoms and chronic pain after mild traumatic brain injury are modulated by multiple locus effect in the BDNF gene through the expression of antisense: A pilot prospective control study

Background: Mild traumatic brain injury (mTBI) often results in post-concussion symptoms, chronic pain, and sleepiness. Genetic factors are thought to play an important role in poor prognosis.

Aims: The aims of this study are to (1) document the prevalence of pain and post-concussion symptoms in mTBI patients in acute and chronic phases (2) determine whether candidate genes predispose to post-concussive symptoms and pain.

Methods: Posttraumatic symptoms, evaluated using the Rivermead Post-Concussion Symptoms Questionnaire, and pain were assessed in 94 mTBI patients in the acute phase as well as in 22 healthy controls. Assessment was repeated in 36 patients after one year who agreed to participate in the follow-up visit. Gene polymorphisms and expression were assessed in mTBI patients and healthy controls.

Results: In the acute phase, mTBI patients with pain (69%) presented more psychological symptoms and sleepiness and were less able to return to work than those without pain. At one year, 19% of mTBI patients had persistent pain and psychological distress. Two haplotypes (H2 and H3) in the brain-derived neurotrophic factor (BDNF) gene were shown to be respectively deleterious and protective against post-concussion symptoms and pain in both acute and chronic phases. Protective haplotype H3 was associated with a decreased expression of the anti-sense of BDNF (BDNF-AS). Deleterious haplotype H2 predicted the development of chronic pain at one year, whereas H3 was protective.

Conclusions: This pilot study suggests a protective mechanism of a multilocus effect in BDNF, through BDNF-AS, against post-concussion symptoms and pain in the acute phase and possibly chronic pain at one year post-mTBI. The role of antisense RNA should be validated in larger cohorts.

COMT, BDNF, and DTNBP1 polymorphisms and cognitive functions in patients with brain tumors

BACKGROUND

Cognitive dysfunction is common among patients with brain tumors and can be associated with the disease and treatment with radiotherapy and chemotherapy. However, little is known about genetic risk factors that may moderate the vulnerability for developing cognitive dysfunction. In this study, we examined the association of single nucleotide polymorphisms (SNPs) in the catechol-O-methyl transferase (COMT), brain-derived neurotrophic factor (BDNF), and dystrobrevin-binding protein 1 (DTNBP1) genes with cognitive functions and neuroimaging outcomes in patients with brain tumors.

METHODS

One hundred and fifty patients with brain tumors completed neuropsychological tests of attention, executive functions, and memory and were genotyped for polymorphisms in the COMT, BDNF, and DTNBP1 genes. Ratings of white matter (WM) abnormalities on magnetic resonance imaging scans were performed.

RESULTS

Multivariate regression shrinkage analyses, adjusted for age, education, treatment type, time since treatment completion, and tumor location, indicated a significant association between the COMT SNP rs4680 (Val158Met) and memory with lower scores in delayed recall (P < .01) among homozygotes (valine/valine). Additional COMT, BDNF and DTNBP1 SNPs were significantly associated with attention, executive functions, and memory scores.

CONCLUSION

This is the first study to suggest that known and newly described polymorphisms in genes associated with executive and memory functions in healthy individuals and other clinical populations may modulate cognitive outcome in patients with brain tumors.

Alpha-synuclein (SNCA) polymorphisms exert protective effects on memory after mild traumatic brain injury

Problems with attention and short-term learning and memory are commonly reported after mild traumatic brain injury (mTBI). Due to the known relationships between α-synuclein (SNCA), dopaminergic transmission, and neurologic deficits, we hypothesized that SNCA polymorphisms might be associated with cognitive outcome after mTBI. A cohort of 91 mTBI patients one month after injury and 86 healthy controls completed a series of cognitive tests assessing baseline intellectual function, attentional function, and memory, and was genotyped at 13 common single nucleotide polymorphisms (SNPs) in the SNCA gene. Significant differences in two memory measures (p=0.001 and 0.002), but not baseline intellectual function or attentional function tasks, were found between the mTBI group and controls. A highly significant protective association between memory performance and SNCA promoter SNP rs1372525 was observed in the mTBI patients (p=0.006 and 0.029 for the long and short delay conditions of the California Verbal Learning Tests, respectively), where the presence of at least one copy of the A (minor) allele was protective after mTBI. These results may help elucidate the pathophysiology of cognitive alterations after mTBI, and thus warrant further investigation.

Missense Mutation of Brain Derived Neurotrophic Factor (BDNF) Alters Neurocognitive Performance in Patients with Mild Traumatic Brain Injury: A Longitudinal Study

The predictability of neurocognitive outcomes in patients with traumatic brain injury is not straightforward. The extent and nature of recovery in patients with mild traumatic brain injury (mTBI) are usually heterogeneous and not substantially explained by the commonly known demographic and injury-related prognostic factors despite having sustained similar injuries or injury severity. Hence, this study evaluated the effects and association of the Brain Derived Neurotrophic Factor (BDNF) missense mutations in relation to neurocognitive performance among patients with mTBI. 48 patients with mTBI were prospectively recruited and MRI scans of the brain were performed within an average 10.1 (SD 4.2) hours post trauma with assessment of their neuropsychological performance post full Glasgow Coma Scale (GCS) recovery. Neurocognitive assessments were repeated again at 6 months follow-up. The paired t-test, Cohen's d effect size and repeated measure ANOVA were performed to delineate statistically significant differences between the groups [wildtype G allele (Val homozygotes) vs. minor A allele (Met carriers)] and their neuropsychological performance across the time point (T1 = baseline/ admission vs. T2 = 6th month follow-up). Minor A allele carriers in this study generally performed more poorly on neuropsychological testing in comparison wildtype G allele group at both time points. Significant mean differences were observed among the wildtype group in the domains of memory (M = -11.44, SD = 10.0, p = .01, d = 1.22), executive function (M = -11.56, SD = 11.7, p = .02, d = 1.05) and overall performance (M = -6.89 SD = 5.3, p = .00, d = 1.39), while the minor A allele carriers showed significant mean differences in the domains of attention (M = -11.0, SD = 13.1, p = .00, d = .86) and overall cognitive performance (M = -5.25, SD = 8.1, p = .01, d = .66).The minor A allele carriers in comparison to the wildtype G allele group, showed considerably lower scores at admission and remained impaired in most domains across the timepoints, although delayed signs of recovery were noted to be significant in the domains attention and overall cognition. In conclusion, the current study has demonstrated the role of the BDNF rs6265 Val66Met polymorphism in influencing specific neurocognitive outcomes in patients with mTBI. Findings were more detrimentally profound among Met allele carriers.

Genetics of structural connectivity and information processing in the brain

Understanding the genetic factors underlying brain structural connectivity is a major challenge in imaging genetics. Here, we present results from genome-wide association studies (GWASs) of whole-brain white matter (WM) fractional anisotropy (FA), an index of microstructural coherence measured using diffusion tensor imaging. Data from independent GWASs of 355 Swedish and 250 Norwegian healthy adults were integrated by meta-analysis to enhance power. Complementary GWASs on behavioral data reflecting processing speed, which is related to microstructural properties of WM pathways, were performed and integrated with WM FA results via multimodal analysis to identify shared genetic associations. One locus on chromosome 17 (rs145994492) showed genome-wide significant association with WM FA (meta P value = 1.87 × 10^-08). Suggestive associations (Meta P value <1 × 10^-06) were observed for 12 loci, including one containing ZFPM2 (lowest meta P value = 7.44 × 10^-08). This locus was also implicated in multimodal analysis of WM FA and processing speed (lowest Fisher P value = 8.56 × 10^-07). ZFPM2 is relevant in specification of corticothalamic neurons during brain development. Analysis of SNPs associated with processing speed revealed association with a locus that included SSPO (lowest meta P value = 4.37 × 10^-08), which has been linked to commissural axon growth. An intergenic SNP (rs183854424) 14 kb downstream of CSMD1, which is implicated in schizophrenia, showed suggestive evidence of association in the WM FA meta-analysis (meta P value = 1.43 × 10^-07) and the multimodal analysis (Fisher P value = 1 × 10^-07). These findings provide novel data on the genetics of WM pathways and processing speed, and highlight a role of ZFPM2 and CSMD1 in information processing in the brain.

Impact of traumatic brain injury on sleep structure, electrocorticographic activity and transcriptome in mice

Traumatic brain injury (TBI), including mild TBI (mTBI), is importantly associated with vigilance and sleep complaints. Because sleep is required for learning, plasticity and recovery, we here evaluated the bidirectional relationship between mTBI and sleep with two specific objectives: (1) Test that mTBI rapidly impairs sleep-wake architecture and the dynamics of the electrophysiological marker of sleep homeostasis (i.e., non-rapid eye movement sleep delta (1-4Hz) activity); (2) evaluate the impact of sleep loss following mTBI on the expression of plasticity markers that have been linked to sleep homeostasis and on genome-wide gene expression. A closed-head injury model was used to perform a 48h electrocorticographic (ECoG) recording in mice submitted to mTBI or Sham surgery. mTBI was found to immediately decrease the capacity to sustain long bouts of wakefulness as well as the amplitude of the time course of ECoG delta activity during wakefulness. Significant changes in ECoG spectral activity during wakefulness, non-rapid eye movement and rapid eye movement sleep were observed mainly on the second recorded day. A second experiment was performed to measure gene expression in the cerebral cortex and hippocampus after a mTBI followed either by two consecutive days of 6h sleep deprivation (SD) or of undisturbed behavior (quantitative PCR and next-generation sequencing). mTBI modified the expression of genes involved in immunity, inflammation and glial function (e.g., chemokines, glial markers) and SD changed that of genes linked to circadian rhythms, synaptic activity/neuronal plasticity, neuroprotection and cell death and survival. SD appeared to affect gene expression in the cerebral cortex more importantly after mTBI than Sham surgery including that of the astrocytic marker Gfap, which was proposed as a marker of clinical outcome after TBI. Interestingly, SD impacted the hippocampal expression of the plasticity elements Arc and EfnA3 only after mTBI. Overall, our findings reveal alterations in spectral signature across all vigilance states in the first days after mTBI, and show that sleep loss post-mTBI reprograms the transcriptome in a brain area-specific manner and in a way that could be deleterious to brain recovery.

Brain arteriovenous malformations

An arteriovenous malformation is a tangle of dysplastic vessels (nidus) fed by arteries and drained by veins without intervening capillaries, forming a high-flow, low-resistance shunt between the arterial and venous systems. Arteriovenous malformations in the brain have a low estimated prevalence but are an important cause of intracerebral haemorrhage in young adults. For previously unruptured malformations, bleeding rates are approximately 1% per year. Once ruptured, the subsequent risk increases fivefold, depending on associated aneurysms, deep locations, deep drainage and increasing age. Recent findings from novel animal models and genetic studies suggest that arteriovenous malformations, which were long considered congenital, arise from aberrant vasculogenesis, genetic mutations and/or angiogenesis after injury. The phenotypical characteristics of arteriovenous malformations differ among age groups, with fistulous lesions in children and nidal lesions in adults. Diagnosis mainly involves imaging techniques, including CT, MRI and angiography. Management includes observation, microsurgical resection, endovascular embolization and stereotactic radiosurgery, alone or in any combination. There is little consensus on how to manage patients with unruptured malformations; recent studies have shown that patients managed medically fared better than those with intervention at short-term follow-up. By contrast, interventional treatment is preferred following a ruptured malformation to prevent rehaemorrhage. Management continues to evolve as new mechanistic discoveries and reliable animal models raise the possibility of developing drugs that might prevent the formation of arteriovenous malformations, induce obliteration and/or stabilize vessels to reduce rupture risk. For an illustrated summary of this Primer, visit: http://go.nature.com/TMoAdn.

Expert consensus document: Mind the gaps—advancing research into short-term and long-term neuropsychological outcomes of youth sports-related concussions

Sports-related concussions and repetitive subconcussive exposure are increasingly recognized as potential dangers to paediatric populations, but much remains unknown about the short-term and long-term consequences of these events, including potential cognitive impairment and risk of later-life dementia. This Expert Consensus Document is the result of a 1-day meeting convened by Safe Kids Worldwide, the Alzheimer's Drug Discovery Foundation, and the Andrews Institute for Orthopaedics and Sports Medicine. The goal is to highlight knowledge gaps and areas of critically needed research in the areas of concussion science, dementia, genetics, diagnostic and prognostic biomarkers, neuroimaging, sports injury surveillance, and information sharing. For each of these areas, we propose clear and achievable paths to improve the understanding, treatment and prevention of youth sports-related concussions.

Impact of repetitive transcranial magnetic stimulation on post-stroke dysmnesia and the role of BDNF Val66Met SNP

Background

Little is known about the effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) on dysmnesia and the impact of brain nucleotide neurotrophic factor (BDNF) Val66Met single-nucleotide polymorphism (SNP). This study investigated the impact of low-frequency rTMS on post-stroke dysmnesia and the impact of BDNF Val66Met SNP.

Material/Methods

Forty patients with post-stroke dysmnesia were prospectively randomized into the rTMS and sham groups. BDNF Val66Met SNP was determined using restriction fragment length polymorphism. Montreal Cognitive Assessment (MoCA), Loewenstein Occupational Therapy of Cognitive Assessment (LOTCA), and Rivermead Behavior Memory Test (RBMT) scores, as well as plasma BDNF concentrations, were measured at baseline and at 3 days and 2 months post-treatment.

Results

MoCA, LOTCA, and RBMT scores were higher after rTMS. Three days after treatment, BDNF decreased in the rTMS group but it increased in the sham group (P<0.05). Two months after treatment, RMBT scores in the rTMS group were higher than in the sham group, but not MoCA and LOTCA scores.

Conclusions

Low-frequency rTMS may improve after-stoke memory through various pathways, which may involve polymorphisms and several neural genes, but not through an increase in BDNF levels.

Genetic predictors of outcome following traumatic brain injury

The nature of traumatic brain injury (TBI) has acute and chronic outcomes for those who survive. Over time, the chronic process of injury impacts multiple organ systems that may lead to disease. We discuss possible mechanisms and methodological issues in the context of candidate gene association studies using TBI patient populations. Because study population sizes have been generally limited, we discussed results on genes that have been the focus of independent studies. We also present a justification for testing more speculative candidate genes in recovery from TBI, such as those involved in circadian rhythm, to outline the importance of prioritizing functional variants in genes that may modulate recovery or provide neuroprotection from TBI. Finally, we provide a perspective on how future research will integrate population level genetic findings with the biological basis of disease in order to create a resource of predictive outcome measures for individual patients.

Outcome prediction after mild and complicated mild traumatic brain injury: external validation of existing models and identification of new predictors using the TRACK-TBI pilot study

Although the majority of patients with mild traumatic brain injury (mTBI) recover completely, some still suffer from disabling ailments at 3 or 6 months. We validated existing prognostic models for mTBI and explored predictors of poor outcome after mTBI. We selected patients with mTBI from TRACK-TBI Pilot, an unselected observational cohort of TBI patients from three centers in the United States. We validated two prognostic models for the Glasgow Outcome Scale Extended (GOS-E) at 6 months after injury. One model was based on the CRASH study data and another from Nijmegen, The Netherlands. Possible predictors of 3- and 6-month GOS-E were analyzed with univariate and multi-variable proportional odds regression models. Of the 386 of 485 patients included in the study (median age, 44 years; interquartile range, 27-58), 75% (n=290) presented with a Glasgow Coma Score (GCS) of 15. In this mTBI population, both previously developed models had a poor performance (area under the receiver operating characteristic curve, 0.49-0.56). In multivariable analyses, the strongest predictors of lower 3- and 6-month GOS-E were older age, pre-existing psychiatric conditions, and lower education. Injury caused by assault, extracranial injuries, and lower GCS were also predictive of lower GOS-E. Existing models for mTBI performed unsatisfactorily. Our study shows that, for mTBI, different predictors are relevant as for moderate and severe TBI. These include age, pre-existing psychiatric conditions, and lower education. Development of a valid prediction model for mTBI patients requires further research efforts.