Chapter 6 state of the science of pediatric traumatic brain injury: biomarkers and gene association studies

A study protocol for risk stratification in children with concussion (RSiCC): Theoretical framework, design, and methods

Research shows that one in five children will experience a concussion by age 16. Compared to adults, children experience longer and more severe postconcussive symptoms (PCS), with severity and duration varying considerably among children and complicating management of these patients. Persistent PCS can result in increased school absenteeism, social isolation, and psychological distress. Although early PCS diagnosis and access to evidence-based interventions are strongly linked to positive health and academic outcomes, symptom severity and duration are not fully explained by acute post-injury symptoms. Prior research has focused on the role of neuroinflammation in mediating PCS and associated fatigue; however relationship between inflammatory biomarkers and PCS severity, has not examined longitudinally. To identify which children are at high risk for persistent PCS and poor health, academic, and social outcomes, research tracking PCS trajectories and describing school-based impacts across the entire first year postinjury is critically needed. This study will 1) define novel PCS trajectory typologies in a racially/ethnically diverse population of 500 children with concussion (11-17 years, near equal distribution by sex), 2) identify associations between these typologies and patterns of inflammatory biomarkers and genetic variants, 3) develop a risk stratification model to identify children at risk for persistent PCS; and 4) gain unique insights and describe PCS impact, including fatigue, on longer-term academic and social outcomes. We will be the first to use NIH's symptom science model and patient-reported outcomes to explore the patterns of fatigue and other physical, cognitive, psychological, emotional and academic responses to concussion in children over a full year. Our model will enable clinicians and educators to identify children most at risk for poor long-term health, social, and academic outcomes after concussion. This work is critical to meeting our long-term goal of developing personalized concussion symptom-management strategies to improve outcomes and reduce disparities in the health and quality of life of children.

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.

Association between Day-to-Day Pulsatility Index Change and Neurocognitive Outcomes in Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) remains a significant cause of morbidity and mortality in children despite advances in prevention and mitigation strategies. Transcranial Doppler (TCD) ultrasound measures cerebral arterial circulation and allows for the calculation of pulsatility indices (PIs), which provides an assessment of cerebral blood flow changes. Yet, the use of PIs in children with TBI is not well understood. In this study, we defined the day-to-day (DTD) PI change of the anterior cerebral circulation and describe its relationship with injury characteristics and neurocognitive outcomes in children with TBI. A prospective observational parent study of 42 children, 2 months to 15 years of age, with mild or moderate-severe TBI who had serial TCDs provided data for this analysis. Both the mean and variation of DTD PI change were evaluated in the context of injury severity, injury sidedness, and neurocognitive outcome. In those with a unilateral injury, a larger mean DTD PI change in both the injured and uninjured side was found in those with a worse Glasgow Outcome Scale-Extended Pediatrics score at discharge. A larger variation in PI was associated with a worse neurocognitive outcome, irrespective of injury severity. Therefore, the mean and variation of DTD PI change may serve as a potential cerebral vascular biomarker of ongoing secondary injury. The use of PI measurements in the monitoring of children with TBI may provide clinicians with new diagnostic and prognostic insights to inform therapeutic interventions and recovery strategies. However, a larger prospective study is needed to confirm these findings and elucidate potential mechanistic links between DTD PI and clinical outcome measures. To our knowledge, this study is the first of its kind to evaluate the use of PI changes in cerebral vasculature in pediatric TBI patients admitted to the hospital.

Pediatric Traumatic Brain Injury: An Update on Preclinical Models, Clinical Biomarkers, and the Implications of Cerebrovascular Dysfunction

Traumatic brain injury (TBI) is a leading cause of pediatric morbidity and mortality. Recent studies suggest that children and adolescents have worse post-TBI outcomes and take longer to recover than adults. However, the pathophysiology and progression of TBI in the pediatric population are studied to a far lesser extent compared to the adult population. Common causes of TBI in children are falls, sports/recreation-related injuries, non-accidental trauma, and motor vehicle-related injuries. A fundamental understanding of TBI pathophysiology is crucial in preventing long-term brain injury sequelae. Animal models of TBI have played an essential role in addressing the knowledge gaps relating to pTBI pathophysiology. Moreover, a better understanding of clinical biomarkers is crucial to diagnose pTBI and accurately predict long-term outcomes. This review examines the current preclinical models of pTBI, the implications of pTBI on the brain’s vasculature, and clinical pTBI biomarkers. Finally, we conclude the review by speculating on the emerging role of the gut-brain axis in pTBI pathophysiology.

Ultrasound-Mediated Blood-Brain Barrier Opening Improves Whole Brain Gene Delivery in Mice

Gene therapy represents a powerful therapeutic tool to treat diseased tissues and provide a durable and effective correction. The central nervous system (CNS) is the target of many gene therapy protocols, but its high complexity makes it one of the most difficult organs to reach, in part due to the blood-brain barrier that protects it from external threats. Focused ultrasound (FUS) coupled with microbubbles appears as a technological breakthrough to deliver therapeutic agents into the CNS. While most studies focus on a specific targeted area of the brain, the present work proposes to permeabilize the entire brain for gene therapy in several pathologies. Our results show that, after i.v. administration and FUS sonication in a raster scan manner, a self-complementary AAV9-CMV-GFP vector strongly and safely infected the whole brain of mice. An increase in vector DNA (19.8 times), GFP mRNA (16.4 times), and GFP protein levels (17.4 times) was measured in whole brain extracts of FUS-treated GFP injected mice compared to non-FUS GFP injected mice. In addition to this increase in GFP levels, on average, a 7.3-fold increase of infected cells in the cortex, hippocampus, and striatum was observed. No side effects were detected in the brain of treated mice. The combining of FUS and AAV-based gene delivery represents a significant improvement in the treatment of neurological genetic diseases.

Day-to-Day Change in Pulsatility Index Describes Anterior Cerebral Circulation Disturbance and Functional Outcomes in Pediatric Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) is a significant source of morbidity and mortality in children. Transcranial Doppler (TCD) ultrasound measures the cerebral arterial circulation allowing for the calculation of pulsatility indices (PIs) that provide an assessment of cerebral blood flow alterations. However, the use of PI in children with TBI is poorly understood and may be an important measure for the nursing care of children.

OBJECTIVES

The purpose of this article is to define day-to-day PI change and to describe its relationship to injury characteristics and functional outcomes in children with TBI.

METHOD

We performed a secondary analysis of a prospective observational parent study of 40 children aged 2 months to 15 years with mild or moderate-severe TBI who had serial TCDs. Sequential TCD PI measurements of day-to-day change revealed several consistencies among the TBI severity groups.

RESULTS

Day-to-day PI change was higher in children with a moderate-severe injury (40%) when compared with those with a mild injury (21%). Greater day-to-day PI change was seen in children whose Glasgow Outcome Scale-Extended Pediatrics scores worsened (25%) compared with those who had an improved (19%) or unchanged (23%) scores.

DISCUSSION

This study is the first to report day-to-day PI change in children with TBI and provides early insights into anterior cerebral artery circulation alterations of children with TBI. Although further research is needed, this study provides early evidence that TCD may be a valuable noninvasive neuromonitoring option in the management of children with TBI.

Best Practices for Obtaining Genomic Consent in Pediatric Traumatic Brain Injury Research

BACKGROUND

Precision health relies on large sample sizes to ensure adequate power, generalizability, and replicability; however, a critical first step to any study is the successful recruitment of participants.

OBJECTIVES

This study seeks to explore how the enrollment strategies used in a parent study contributed to the high consent rates, establish current best practices that can be used in future studies, and identify additional factors that contribute to consent into pediatric traumatic brain injury biobanks.

METHODS

Retrospective secondary analysis of data from a parent study with high consent rates was examined to explore factors affecting consent into biobanking studies.

RESULTS

Of the 76 subjects who were approached, met the eligibility criteria, and reviewed the consent form, only 16 (21.1%) declined to participate. The consented group (n = 60) represents 64.5% of those who met the eligibility criteria upon initial screening (n = 93) and 78.9% of those with confirmed eligibility (n = 76). Analysis of screening data suggested there were no major barriers to consenting individuals into this pediatric traumatic brain injury biobank.

DISCUSSION

There were no demographic or research-related characteristics that significantly explained enrollment. Ethically, to obtain true informed consent, parents need to understand only their child's diagnosis, prognosis, and medical care, as well as the purpose of the proposed research and its risks and benefits. Researchers need to implement best practices, including a comprehensive review of census data to identify eligible participants to approach, a prescreening protocol, and effective consenting process to obtain informed consent so that precision care initiatives can be pursued.

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

BACKGROUND

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

OBJECTIVE

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

METHOD

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

RESULTS

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

CONCLUSION

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

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

BACKGROUND/AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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