Apolipoprotein E epsilon4 associated with chronic traumatic brain injury in boxing.
Level 4 - case-series / case-control
Cross-sectional observational study
What was done
Thirty professional boxers (24 volunteers and 6 clinical referrals, aged 23 to 76 years) underwent neurologic and behavioral assessments and APOE genotyping. Severity of traumatic encephalopathy was measured using a 10-point Chronic Brain Injury (CBI) scale (0–9) and analyzed according to boxing exposure (high exposure defined as ≥12 professional bouts vs low exposure) and APOE genotype.
What was found
Among the 30 boxers, 11 scored 0 (normal), 12 scored 1–2 (mild deficits), 4 scored 3–4 (moderately impaired), and 3 scored >4 (severe impairment). High-exposure boxers had significantly higher CBI scores (mean [SD], 2.6 [1.9]) than low-exposure boxers (mean [SD], 0.3 [0.7]) (P < .001). Low-exposure boxers averaged 0.33 regardless of APOE status. Among high-exposure boxers, those with an APOE epsilon4 allele had significantly higher CBI scores (mean [SD], 3.9 [2.3]) than those without epsilon4 (mean [SD], 1.8 [1.2]) (P = .04). All boxers with severe impairment possessed at least one APOE epsilon4 allele (P < .001 for the combined effect of high exposure and epsilon4).
Why it matters
This study provides early preliminary evidence that genetic variation, specifically the APOE epsilon4 allele, may increase vulnerability to chronic neurologic deficits following repetitive head trauma in contact sports.
Limits
The study sample was small (n = 30) with only 3 severely impaired individuals. The cross-sectional design prevents establishing longitudinal progression or causality, and combining volunteer and clinical referral subjects introduces potential selection bias.
Cited by
- contradicts Boxers carrying the APOE e4 gene show cognitive impairment after an average of 11 fights, whereas non-carriers do not show cognitive impairment until after approximately 30 fights.