Associations of Apolipoprotein E ε4 Genotype and Ball Heading With Verbal Memory in Amateur Soccer Players

Soccer (football) and brain health

Soccer is one of the most popular sports worldwide, played by over 270 million people and followed by many more. Several brain health benefits are promoted by practising soccer and physical exercise at large, which helps contrast the cognitive decline associated with ageing by enhancing neurogenesis processes. However, sport-related concussions have been increasingly recognised as a pressing public health concern, not only due to their acute impact but also, more importantly, due to mounting evidence indicating an elevated risk for the development of neurological sequelae following recurrent head traumas, especially chronic traumatic encephalopathy (CTE). While soccer players experience less frequent concussions compared with other contact or combat sports, such as American football or boxing, it stands alone in its purposeful use of the head to hit the ball (headings), setting its players apart as the only athletes exposed to intentional, sub-concussive head impacts. Additionally, an association between soccer and amyotrophic lateral sclerosis has been consistently observed, suggesting a potential "soccer-specific" risk factor. In this review, we discuss the neurological sequelae related to soccer playing, the emerging evidence of a detrimental effect related to recurrent headings, and the need for implementation of comprehensive strategies aimed at preventing and managing the burden of head impact in soccer.

Chronic Traumatic Encephalopathy in Soccer Players: Review of 14 Cases

OBJECTIVE

Exposure to repetitive sports-related concussions or (sub)concussive head trauma may lead to chronic traumatic encephalopathy (CTE). Which impact (heading or concussion) poses the greatest risk of CTE development in soccer players?

DESIGN

Narrative review.

SETTING

Teaching hospital and University of Applied sciences.

PATIENTS

A literature search (PubMed) was conducted for neuropathologic studies in the period 2005-December 2022, investigating soccer players with dementia and a CTE diagnosis, limited to English language publications. 210 papers were selected for final inclusion, of which 7 papers described 14 soccer players.

ASSESSMENT

Magnetic resonance imaging studies in soccer players show that lifetime estimates of heading numbers are inversely correlated with cortical thickness, grey matter volume, and density of the anterior temporal cortex. Using diffusion tensor imaging-magnetic resonance imaging, higher frequency of headings-particularly with rotational accelerations-are associated with impaired white matter integrity. Serum neurofilament light protein is elevated after heading.

MAIN OUTCOME MEASURES

Chronic traumatic encephalopathy pathology, history of concussion, heading frequency.

RESULTS

In 10 of 14 soccer players, CTE was the primary diagnosis. In 4 cases, other dementia types formed the primary diagnosis and CTE pathology was a concomitant finding. Remarkably, 6 of the 14 cases had no history of concussion, suggesting that frequent heading may be a risk for CTE in patients without symptomatic concussion. Rule changes in heading duels, management of concussion during the game, and limiting the number of high force headers during training are discussed.

CONCLUSIONS

Data suggest that heading frequency and concussions are associated with higher risk of developing CTE in (retired) soccer players. However based on this review of only 14 players, questions persist as to whether or not heading is a risk factor for CTE or long-term cognitive decline.

The brain's weakness in the face of trauma: How head trauma causes the destruction of the brain

Of all our organs, the brain is perhaps the best protected from trauma. The skull has evolved to enclose it and, within the skull, the brain floats in a protective bath of cerebrospinal fluid. It is becoming evident, however, that head trauma experienced in young adult life can cause a dementia that appears decades later. The level of trauma that induces such destruction is still being assessed but includes levels well below that which cracks the skull or causes unconsciousness or concussion. Clinically this damage appears as dementia, in people who played body-contact sports in their youth or have survived accidents or the blasts of combat; and appears also, we argue, in old age, without a history of head trauma. The dementias have been given different names, including dementia pugilistica (affecting boxers), chronic traumatic encephalopathy (following certain sports, particularly football), traumatic brain injury (following accidents, combat) and Alzheimer's (following decades of life). They share common features of clinical presentation and neuropathology, and this conceptual analysis seeks to identify features common to these forms of brain injury and to identify where in the brain the damage common to them occurs; and how it occurs, despite the protection provided by the skull and cerebrospinal fluid. The analysis suggests that the brain's weak point in the face of trauma is its capillary bed, which is torn by the shock of trauma. This identification in turn allows discussion of ways of delaying, avoiding and even treating these trauma-induced degenerations.

Age of first exposure to soccer heading: Associations with cognitive, clinical, and imaging outcomes in the Einstein Soccer Study

Introduction

The objective of this study is to assess the role of age at first exposure (AFE) to soccer heading as a predictor of known adverse associations of recent and longer-term heading with brain microstructure, cognitive, and behavioral features among adult amateur soccer players.

Methods

The sample included 276 active amateur soccer players (196 male and 81 female) aged 18-53 years old. AFE to soccer heading was treated as a binary variable, dichotomized at ≤ 10 years vs. >10 years old, based on a recently promulgated US Soccer policy, which bans heading for athletes ages 10 and under.

Results

We found that soccer players who began heading at age 10 or younger performed better on tests of working memory (p = 0.03) and verbal learning (p = 0.02), while accounting for duration of heading exposure, education, sex, and verbal intelligence. No difference in brain microstructure or behavioral measures was observed between the two exposure groups.

Discussion

The findings indicate that, among adult amateur soccer players, AFE to heading before age 10 compared to later start of heading, is not associated with adverse outcomes, and may be associated with better cognitive performance in young adulthood. Cumulative heading exposure across the lifespan, rather than early life exposure, may drive risk for adverse effects and should be the focus of future longitudinal studies to inform approaches to enhance player safety.

Football (Soccer) as a Probable Cause of Long-Term Neurological Impairment and Neurodegeneration: A Narrative Review of the Debate

Football (soccer) is the most widely played sport across the globe. Due to some recent high-profile cases and epidemiological studies suggesting football can lead to neurodegeneration, scientific and public interest has been piqued. This has resulted in research into whether an association between football participation and neurodegeneration or neurological impairment is present. It has been theorised that a combination of repeated sub-concussive and concussive injuries, due to ball-heading and head collisions, may lead to neurodegeneration. However, evidence remains conflicting. Due to the popularity of the sport, and the serious conditions it has been linked to, it is important to determine whether repeated head impacts during football participation can play a causative role in neurodegenerative disease. To answer this question, a review of the current literature was carried out. Epidemiological evidence showed a higher incidence of amyotrophic lateral sclerosis amongst amateur and professional footballers and that footballers in positions that involve less contact and heading, e.g., goalkeepers lead significantly longer lives. Additionally, imaging studies reach a similar conclusion, reporting changes in brain structure, blood flow, and inflammatory markers in footballers when compared to controls. However, studies looking at an association between heading frequency and cognition show a lack of consensus on whether a higher heading exposure results in reduced cognition. Similarly, in neuropathological studies, signs of chronic traumatic encephalopathy (CTE) have been found in some former players, with contrasting studies suggesting low levels of CTE-type pathology are found in the general population, regardless of exposure to head trauma. The majority of studies suggest a link between football and neurodegenerative disease. However, the high prevalence of retrospective cohort and cross-sectional studies, often plagued by recall bias, undermine the conclusions drawn. Therefore, until larger prospective cohort studies are conducted, concrete conclusions cannot be made. However, caution can be exercised to limit head impacts.

Cerebral blood flow regulation is not acutely altered after a typical number of headers in women footballers

BACKGROUND

The repeated act of heading has been implicated in the link between football participation and risk of neurodegenerative disease, and acutely alters cerebrovascular outcomes in men. This study assessed whether exposure to a realistic number of headers acutely influences indices of cerebral blood flow regulation in female footballers.

METHODS

Nineteen female players completed a heading trial and seated control trial on two separate days. The heading trial involved six headers in 1 h (one every 10 min), with the ball traveling at 40 ± 5 km/h. Cerebrovascular reactivity to hypercapnia and hypocapnia was determined using serial breath holding and hyperventilation attempts. Dynamic cerebral autoregulation (dCA) was assessed by scrutinizing the relationship between cerebral blood flow and mean arterial blood pressure during 5 min of squat stand maneuvers at 0.05 Hz. Neurovascular coupling (NVC) was quantified as the posterior cerebral artery blood velocity response to a visual search task. These outcomes were assessed before and 1 h after the heading or control trial.

RESULTS

No significant time by trial interaction was present for the hypercapnic (P = 0.48,η p 2 = 0.05) and hypocapnic (P = 0.47,η p 2 = 0.06) challenge. Similarly, no significant interaction effect was present for any metric of dCA (P > 0.12,η p 2 < 0.16 for all) or NVC (P > 0.14,η p 2 < 0.15 for all).

CONCLUSION

The cerebral blood flow response to changes in carbon dioxide, blood pressure and a visual search task were not altered following six headers in female footballers. Further study is needed to observe whether changes are apparent after more prolonged exposure.

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.

Apolipoprotein e (APOE) ε4 genotype influences memory performance following remote traumatic brain injury in U.S. military service members and veterans

The purpose of this study was to examine the association between the apolipoprotein E (APOE) ε4 allele and neurocognitive functioning following traumatic brain injury (TBI) in military service members and veterans (SMVs). Participants included 176 SMVs with a history of remote TBI (≥1 year post-injury), categorized into mild (n = 100), moderate (n = 40), and severe (n = 36) TBI groups. Participants completed a neuropsychological assessment and APOE genotyping (n = 46 ε4+, n = 130 ε4-). Neurocognitive composite scores representing memory, executive functioning, and visual processing speed were computed. ANCOVAs adjusting for race, education, combat exposure, and PTSD symptom severity showed a significant main effect of ε4 on the memory composite, such that ε4+ SMVs exhibited poorer memory performance than ε4- SMVs. When ε2 allele carriers were removed from the analyses, associations with memory were strengthened, demonstrating a possible protective effect of the ε2 allele. No main effect of TBI group was identified on any cognitive composite, nor were there any significant TBI group × ε4 status interactions for any cognitive composite. Future studies with larger samples are needed to verify these findings, but our results suggest an important relationship between ε4 status and memory functioning following remote TBI of all severities.

APOE Genotype and Alzheimer's Disease: The Influence of Lifestyle and Environmental Factors

Alzheimer's disease (AD) is the most common neurodegenerative disorder with obscure pathogenesis and no disease-modifying therapy to date. AD is multifactorial disease that develops from the complex interplay of genetic factors and environmental exposures. The E4 allele of the gene encoding apolipoprotein E (APOE) is the most common genetic risk factor for AD, whereas the E2 allele acts in a protective manner. A growing amount of epidemiological evidence suggests that several lifestyle habits and environmental factors may interact with APOE alleles to synergistically affect the risk of AD development. Among them, physical exercise, dietary habits including fat intake and ketogenic diet, higher education, traumatic brain injury, cigarette smoking, coffee consumption, alcohol intake, and exposure to pesticides and sunlight have gained increasing attention. Although the current evidence is inconsistent, it seems that younger APOE4 carriers in preclinical stages may benefit mostly from preventive lifestyle interventions, whereas older APOE4 noncarriers with dementia may show the most pronounced effects. The large discrepancies between the epidemiological studies may be attributed to differences in the sample sizes, the demographic characteristics of the participants, including age and sex, the methodological design, and potential related exposures and comorbidities as possible cofounding factors. In this Review, we aim to discuss available evidence of the prominent APOE genotype-environment interactions in regard to cognitive decline with a focus on AD, providing an overview of the current landscape in this field and suggesting future directions.

On the prevention and treatment of Alzheimer's disease: Control the promoters and look beyond the brain

Alzheimer's disease (AD) is a progressive incurable neurodegenerative disease of the brain afflicting a third of the population aged 85 and older. Pathologic hallmarks include extracellular plaques of amyloid-beta (Aß), intraneuronal neurofibrillary tangles of hyperphosphorylated tau protein, synaptic destruction, neuronal death, and brain atrophy. Neuroinflammation, mediated by microglia, is a central component of the disease, and is intricately connected with peripheral inflammation. The clinical manifestations include progressive memory loss and eventual death. The present treatment of AD is largely ineffective. Nearly all AD is late-onset and presents age 65 or older, and the most common genetic risk factor is carriage of an apolipoprotein (APO) E4 allele, seen in about 25% of the general population. Individuals carrying an APOE4 allele produce more Aß and clear it less efficiently from the brain throughout life. There has been accumulating pathologic and clinical evidence that microbes, particularly the herpes simplex virus (HSV), is a causative factor for AD, most notable in carriers of the APOE4 allele. Eighty percent of the adult population harbors HSV and it resides in the trigeminal ganglion in latent state throughout life, but periodically reactivates, traveling antegrade resulting in herpes labialis and traveling retrograde into the brain leading to neuroinflammation. Functioning as an antimicrobial peptide, Aß inactivates HSV and the recurring process culminates in a buildup of Aß plaque and other hallmarks of AD over time. Periodontal disease exists in 20-50% of the adult population and is also a causative factor for AD. Accordingly, bacteria causing periodontal disease and their byproducts can enter the brain directly via the trigeminal nerve or indirectly through the bloodstream, resulting in AD pathology over time. There are many other promoters of AD, particularly inflammatory conditions outside of the brain, that can be mitigated. Small trials are finally in progress testing antimicrobial drugs for the prevention and treatment of AD. In the meantime, a more proactive approach to the prevention and treatment of AD is posited, with an emphasis on prevention, since the pathologic underpinnings of the disease start decades before the clinical manifestations. Individuals can be stratified in risk categories using family history, periodontal disease presence, APOE4 carriage, and HSV IgG positivity. Moderate- and high-risk individuals can be treated safely with various preventive measures and appropriate antimicrobial agents as discussed. Importantly, the proposed treatments are concordant with the accepted practice of medicine, and if utilized, could significantly decrease AD prevalence.

Impaired cerebral blood flow regulation and cognition in male football players

Football players are at increased risk of neurodegeneration, the likely consequence of repetitive mechanical trauma caused by heading the ball. However, to what extent a history of heading the ball affects cerebral blood flow (CBF) regulation and its potential relationship to cognitive impairment is unknown. To address this, we recruited 16 concussion-free male amateur football players (age: 25 ± 6 y) with a history of heading the ball (18 ± 6 y) and 18 sex, age, education, and activity-matched controls with no prior history of contact sport participation or concussion. Cerebral perfusion was measured at rest and in response to both hyper/hypocapnia to determine cerebrovascular reactivity to carbon dioxide (CVR_{CO2HYPER/HYPO} ) using transcranial Doppler ultrasound and capnography, with the sum reflecting the cerebral vasomotor range. Cognition and visuomotor coordination were assessed using the Montreal cognitive assessment (MoCA) and the Grooved Pegboard Dexterity Test (GPD), respectively. While no differences in cerebral perfusion were observed (p = 0.938), CVR_{CO2HYPER/HYPO} (p = 0.038/p = 0.025), cerebral vasomotor range (p = 0.002), MoCA (p = 0.027), and GPD performance (dominant hand, P ≤ 0.001) were consistently lower in the players compared to controls. These findings are the first to demonstrate that CBF regulation and cognition are collectively impaired in male football players with history of heading the ball, which may contribute to neurodegeneration.

Environmental Risk Factors for Early-Onset Alzheimer's Dementia and Frontotemporal Dementia: A Case-Control Study in Northern Italy

Background: Early-onset dementia (EOD) is defined as dementia with symptom onset before 65 years. The role of environmental risk factors in the etiology of EOD is still undefined. We aimed at assessing the role of environmental risk factors in EOD etiology, taking into account its different clinical types. Methods: Using a case-control study, we recruited all EOD cases referred to Modena hospitals from 2016 to 2019, while the referent population was drawn from cases' caregivers. We investigated residential history, occupational and environmental exposures to chemicals and lifestyle behaviors through a self-administered questionnaire. We computed the odds ratios of EOD risk (overall and restricting to the Alzheimer's dementia (AD) or frontotemporal dementia (FTD) diagnoses) and the corresponding 95% confidence intervals using an unconditional logistic regression model. Results: Fifty-eight EOD patients (19 FTD and 32 AD) and 54 controls agreed to participate. Most of the investigated exposures, such as occupational exposure to aluminum, pesticides, dyes, paints or thinners, were associated with an increased odds ratio (OR) for FTD but not for AD. Long-term use of selenium-containing dietary supplements was associated with increased OR for EOD and, particularly, for FTD. For both EOD forms, smoking and playing football showed an increased odds ratio, while cycling was associated with increased risk only in FTD. Overall sports practice appeared to be a protective factor for both types. Conclusions: Our results suggest a role of environmental and behavioral risk factors such as some chemical exposures and professional sports in EOD etiology, in particular with reference to FTD. Overall sports practice may be associated with a reduced EOD risk.

Heading in the Right Direction: A Critical Review of Studies Examining the Effects of Heading in Soccer Players

The practice of heading in soccer has become a public concern because of the potential for subconcussive impacts to cause cumulative concussive-like effects; however, experimental evidence for this hypothesis has been mixed. This systematic review used pre-defined search parameters to assess primary literature that examined changes in cognitive, behavioral, structural, and/or biological processes after acute heading exposure in youth and young adult soccer players. The findings were synthesized into a concise and comprehensive summary of the research following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) format, and suggestions for standardization of acute heading protocols are described. A total of 1189 articles were considered for this review, with 19 articles meeting all of the inclusion criteria for full analysis. An attempt was made to identify methods with significant sensitivity and reliability by grouping studies based on their outcome measures. Because of lack of standardization across intervention types and data collection protocols, no sensitive and reliable methods could be identified conclusively to assess the effects of acute heading exposure in soccer players. Based on this review, there is not enough evidence to either support or refute the potential of effects of subconcussive events from acute soccer heading exposure. Recommendations for standardization of acute heading exposure studies based on the included literature are discussed. Standardization is required to better understand the impact of acute heading exposure in soccer players, while allowing for the development of guidelines that mitigate any potential risks and allowing athletes to remain active and develop their skills.

Sex Differences in Circulating T-Tau Trajectories After Sports-Concussion and Correlation With Outcome

Sex differences in molecular biomarkers after sports-related concussion (SRC) could steadily advance our understanding of injury heterogeneity and complexity, and help capture phenotypic characteristics, by unveiling sex-dependent pathobiological processes and disease mechanisms. Such knowledge will help improve diagnosis, clinical management, and prognosis. Total-tau (t-tau) has recently emerged as a promising blood marker showing sex-associated differences in neurodegenerative diseases. Nonetheless, to date, little is known about the potential influence of sex on its injury-related concentration and dynamics after SRC. We hypothesized that measurements of circulating levels of t-tau over time would reflect a differential vulnerability signature, providing insights into the sex-related phenotypes and their relationship with clinical outcomes. To test this hypothesis, plasma levels of t-tau were measured using an ultrasensitive immunoassay up to 7 days after injury, in 46 concussed athletes (20 males, 26 females). We used trajectory analysis to generate two distinct temporal profiles of t-tau, which were then compared with gender and return to play (RTP). The majority of subjects (~63%) started with low t-tau concentrations that further declined within the first 48 h; while the remaining (“maximal decliners”) started with concentrations comparable to the baseline levels that also fell over time, but persisting markedly higher compared with the first profile. The maximal decliner group was primarily composed of female subjects (p = 0.007) and was significantly associated with poor outcome (RTP ≥ 10 days after concussion) (p = 0.011). Taken together, our data provide evidence for the existence of sex-related biosignatures following sports-related concussions, possibly indicating a differential effect as a result of distinct brain vulnerability and inherent injury response. Future studies will be required to further elucidate underlying sex-based biological and pathophysiological mechanisms, and determine the value of t-tau signatures for management and therapeutic decision-making in sports-related concussions.