Effect of angiotensin-converting enzyme tag single nucleotide polymorphisms on the outcome of patients with traumatic brain injury

Candidate neuroinflammatory markers of cerebral autoregulation dysfunction in human acute brain injury

The loss of cerebral autoregulation (CA) is a common and detrimental secondary injury mechanism following acute brain injury and has been associated with worse morbidity and mortality. However patient outcomes have not as yet been conclusively proven to have improved as a result of CA-directed therapy. While CA monitoring has been used to modify CPP targets, this approach cannot work if the impairment of CA is not simply related to CPP but involves other underlying mechanisms and triggers, which at present are largely unknown. Neuroinflammation, particularly inflammation affecting the cerebral vasculature, is an important cascade that occurs following acute injury. We hypothesise that disturbances to the cerebral vasculature can affect the regulation of CBF, and hence the vascular inflammatory pathways could be a putative mechanism that causes CA dysfunction. This review provides a brief overview of CA, and its impairment following brain injury. We discuss candidate vascular and endothelial markers and what is known about their link to disturbance of the CBF and autoregulation. We focus on human traumatic brain injury (TBI) and subarachnoid haemorrhage (SAH), with supporting evidence from animal work and applicability to wider neurologic diseases.

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.

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.

Genetics of Chronic Traumatic Encephalopathy

Although chronic traumatic encephalopathy (CTE) garners substantial attention in the media and there have been marked scientific advances in the last few years, much remains unclear about the role of genetic risk in CTE. Two athletes with comparable contact-sport exposure may have varying amounts of CTE neuropathology, suggesting that other factors, including genetics, may contribute to CTE risk and severity. In this review, we explore reasons why genetics may be important for CTE, concepts in genetic study design for CTE (including choosing controls, endophenotypes, gene by environment interaction, and epigenetics), implicated genes in CTE (including APOE, MAPT, and TMEM106B), and whether predictive genetic testing for CTE should be considered.

Cumulative Influence of Inflammatory Response Genetic Variation on Long-Term Neurobehavioral Outcomes after Pediatric Traumatic Brain Injury Relative to Orthopedic Injury: An Exploratory Polygenic Risk Score

The addition of genetic factors to prognostic models of neurobehavioral recovery following pediatric traumatic brain injury (TBI) may account for unexplained heterogeneity in outcomes. The present study examined the cumulative influence of candidate genes involved in the inflammatory response on long-term neurobehavioral recovery in children with early childhood TBI relative to children with orthopedic injuries (OI). Participants were drawn from a prospective, longitudinal study evaluating outcomes of children who sustained TBI (n = 67) or OI (n = 68) between the ages of 3 and 7 years. Parents completed ratings of child executive function and behavior at an average of 6.8 years after injury. Exploratory unweighted and weighted polygenic risk scores (PRS) were constructed from single nucleotide polymorphisms (SNPs) across candidate inflammatory response genes (i.e., angiotensin converting enzyme [ACE], brain-derived neurotrophic factor [BDNF], interleukin-1 receptor antagonist [IL1RN], and 5'-ectonucleotidase [NT5E]) that showed nominal (p ≤ 0.20) associations with outcomes in the TBI group. Linear regression models tested the PRS × injury group (TBI vs. OI) interaction term and post-hoc analyses examined the effect of PRS within each injury group. Higher inflammatory response PRS were associated with more executive dysfunction and behavior problems in children with TBI but not in children with OI. The cumulative influence of inflammatory response genes as measured by PRS explained additional variance in long-term neurobehavioral outcomes, over and above well-established predictors and single candidate SNPs tested individually. The results suggest that some of the unexplained heterogeneity in long-term neurobehavioral outcomes following pediatric TBI may be attributable to a child's genetic predisposition to a greater or lesser inflammatory response to TBI.

Assessment of TREM2 rs75932628 variant's association with Parkinson's disease in a Greek population and Meta-analysis of current data

BACKGROUND

Α number of genetic variants are considered to confer susceptibility to Parkinson's disease (PD). Rs75392628 (R47H), a rare variant of TREM2 gene, has been linked to PD, although its role on PD remains conflicting.

OBJECTIVE

Detection of a possible contribution of rs75392628 variant of TREM2 gene to PD risk.

METHODS

A total of 358 PD patients and 358 healthy controls genotyped for rs75392628. In addition, a meta-analysis was performed by merging our results with those from previous studies.

RESULTS

The rare variant of rs75932628 (47H) of TREM2 gene was not detected on cohort. Meta-analysis of a total of 9271 PD cases and 9777 controls across 14 independent PD data sets from 9 studies, including the present study, did not show any statistically significant effect of rs75392628 on PD risk (OR_FE:1.54 95% CI:0.87-2.73. OR_RE: 1.54, 95%CI: 0.71-3.32).

CONCLUSIONS

Rs75392628 TREM2 variant is rather unlikely to be a major genetic risk contributor of PD.

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 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.

Effect of integrin AV and B8 gene polymorphisms in patients with traumatic brain injury

Background: Α few genetic variants are associated with the outcome after traumatic brain injury (TBI). Integrins are glycoprotein receptors that play an important role in the integrity of microvasculature of the brain. Objective: To examine the role of integrin-AV (ITGAV) and integrin-B8 (ITGB8) tag single nucleotide polymorphisms (SNPs) on the outcome of patients with TBI. Methods: 363 participants were included and genotyped for 11 SNPs for ITGAV and 11 for ITGB8 gene. SNPs were tested for associations with the 6-month outcome after TBI, the presence of a hemorrhagic event after TBI, and the initial TBI severity after adjustment for TBI's main predictors. Results: The ITGAV rs3911239 CC and rs7596996 GG genotypes were associated with an unfavorable outcome after TBI, compared to the TT and AA genotypes, respectively. The ITGB8 rs10239099 CC and rs3757727 CC genotypes were associated with increased risk of any cerebral hemorrhagic event after TBI compared to GG and TT respectively. The ITGAV rs7589470 and rs7565633 were associated with the TBI's initial severity. Conclusions: ITGAV gene SNPs may be implicated in the outcome after TBI, as well as in the initial TBI severity, and also of ITGB8 gene SNPs in the risk of hemorrhagic event after a TBI.

ERCC6L2 rs591486 polymorphism and risk for amyotrophic lateral sclerosis in Greek population

BACKGROUND

Α number of genetic variants have been associated with amyotrophic lateral sclerosis (ALS). A recent study supports that rs591486 across the ERCC6L2 gene and exposure to pesticides seem to have a joint effect on the development of Parkinson's disease, a disease which shares a few common characteristics with ALS.

OBJECTIVE

To detect a possible contribution of rs591486 ERCC6L2 to ALS.

METHODS

A total of 155 patients with ALS and 155 healthy controls were included in the study and genotyped for rs591486. Using logistic regression analyses (crude and adjusted for age and sex), rs591486 was tested for association with ALS risk. Subgroup analysis based on ALS site of onset was also performed. Cox regression analysis was applied in order for the effect of ERCC6L2 rs591486 on ALS age of onset to be tested.

RESULTS

Adjusted analysis showed that ERCC6L2 rs591486 was associated with an increased risk of ALS development, in dominant [odds ratio, OR (95% confidence interval, CI) 2.15 (1.04-4.46), p = 0.037] and over-dominant [OR (95%CI) = 1.91 (1.01-3.60), p = 0.043], modes. Subgroup analysis based on ALS site of onset revealed an association between ERCC6L2 rs591486 and ALS with limb onset. Results for Cox regression analysis indicated that G/A carriers had a lower age of ALS limb onset when compared to G/G carriers.

CONCLUSIONS

The current study provides preliminary indication for an implication of ERCC6L2 rs591486 in ALS development, as a possible genetic risk factor. These results possibly suggest that oxidative stress may be the main contributor in the pathophysiology of ALS.

Lack of Association of the rs11655081 ARSG Gene with Blepharospasm

Blepharospasm (BSP) is a sub-phenotype of focal dystonia. A few genetic risk factors are considered to be implicated in the risk of developing BSP. There is recent evidence, based on results from GWAS and meta-analyses, to suggest that arylsulfatase G (ARSG), and more specifically rs11655081, is implicated in focal dystonia. The aim of the present study was to evaluate the effect of rs11655081 ARSG on BSP. A Greek cohort, which consisted of 206 BSP patients and an equal number of healthy controls, was genotyped for rs11655081. Only a marginal trend for the association between rs11655081 and the risk of BSP was found in the over-dominant model of inheritance [odds ratio, OR (95% confidence interval, CI): 0.64 (0.38-1.07), p = 0.088]. It is rather unlikely that rs11655081 across ARSG is a major genetic risk contributor for BSP.

AQP4 tag SNPs in patients with intracerebral hemorrhage in Greek and Polish population

BACKROUND

A relatively small number of genetic variants are implicated to pathophysiology of intracerebral hemorrhage (ICH). Aquaporin-4 (AQP4) has been reported to be implicated in the pathophysiological processes of ICH development.

OBJECTIVE

To examine the role of AQP4 gene region polymorphisms on the ICH risk.

METHODS

A total of 250 Greek and 193 Polish patients with primary ICH and 250 and 322 respective controls were enrolled, forming two independent cohorts in order to validate any significant effect. With logistic regression analyses, 7 AQP4 tag single nucleotide polymorphisms (SNPs) were examined for association with ICH risk, lobar/non-lobar ICH risk, and 6-month disability after ICH. Cox regression analysis was applied in order to the effect of AQP4 SNPs on ICH age of onset be tested. Correction for multiple comparisons was applied.

RESULTS

Multivariate logistic regression analysis showed that rs3875089 in the Greek cohort and rs3763043, rs335931 in the Polish cohort had a significant influence on the risk of ICH, lobar and non-lobar ICH. Regarding the age of onset, rs3875089 in the Greek cohort and rs3763043, rs11661256 in the Polish cohort were found to significantly alter the age of onset of ICH and its subtypes. However, all of the above associations did not survive the Bonferroni correction (p-value >0.007). Finally, AQP4 tag SNPs were not found to have any significant effect on long-term disability after ICH.

CONCLUSIONS

In conclusion, the present study provides an indication that AQP4 gene variants may affect susceptibility to primary ICH and may influence the ICH age of onset.

CpG Island Methylation Patterns in Relapsing-Remitting Multiple Sclerosis

DNA methylation may predispose to multiple sclerosis (MS), as aberrant methylation in the promoter regions across the genome seems to underlie several processes of MS. We have currently determined the methylation status of eight genes in relapsing-remitting MS patients. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) was used to determine the status of 31 CpG islands, located across eight genes, in 33 healthy individuals and 66 MS patients (33 in relapse and 33 in remission). The methylation levels in the examined sites ranged from 0 to 31%. Methylation positivity for RUNX3 and CDKN2A differed significantly between MS patients and healthy controls. Maximum methylation in RUNX3, CDKN2A, SOCS1, and NEUROG1 genes was significantly different between patients and controls. Roc curves demonstrated that the appropriate cut-offs to distinguish patients from healthy controls were 2% for RUNX3 (OR 3.316, CI 1.207-9.107, p = 0.024) and 3% for CDKN2A (OR 3.077, CI 1.281-7.39, p = 0.018). No difference in methylation was observed between patients in relapse and patients in remission, in any of the genes examined. Methylation patterns of RUNX3 and CDKN2A may be able to distinguish between MS patients and healthy controls, but not between MS patients in relapse and in remission. Graphical Abstract Methylation patterns of RUNX3 and CDKN2A may be able to discriminate healthy individuals from MS patients.

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.

Integrins AV and B8 Gene Polymorphisms and Risk for Intracerebral Hemorrhage in Greek and Polish Populations

Α limited number of genetic variants have been linked to the development of intracerebral hemorrhage (ICH). Ιntegrin AV and/or B8-deficient mice were found to develop ICH. The present candidate gene association study was designed to investigate possible influence of integrin AV (ITGAV) and integrin B8 (ITGB8) gene region polymorphisms on the risk of ICH. 1015 participants (250 Greek and 193 Polish patients with primary ICH and 250 Greek and 322 Polish controls) were included in the study. Using logistic regression analyses, 11 tag single nucleotide polymorphisms (SNPs) for ITGAV and 11 for ITGB8 gene were tested for associations with ICH risk, lobar ICH risk and non-lobar ICH after adjustment for age, gender, history of hypertension and country of origin. Linear regression models were used to test the effect of tag SNPs on the ICH age of onset. Correction for multiple comparisons was carried out. The rs7565633 tag SNP of the ITGAV gene was independently associated with the risk of lobar ICH in the codominant model of inheritance [odds ratio (95 % confidence interval (CI)) 0.56 (0.36-0.86), p = 0.0013]. Furthermore, heterozygous individuals of the rs10251386 and the rs10239099 of the ITGB8 gene had significantly lower age of ICH onset compared to the wild-type genotypes [regression coefficient (b) -3.884 (95 % CI -6.519, -1.249), p = 0.0039 and b = -4.502 (95 % CI -7.159, -1.845), p = 0.0009, respectively]. The present study provides preliminary indication for an influence of ITGAV gene tag SNP in the development of lobar ICH and of ITGB8 gene variants in the age of ICH onset.