Prognostic Value of Apolipoprotein E Epsilon4 Allele in Patients with Traumatic Brain Injury: A Meta-Analysis and Meta-Regression

Aims: Current scientific evidence suggests that the apolipoprotein E epsilon4 (APOE4) allele may be associated with a good prognosis for patients with traumatic brain injury (TBI); however, many existing studies have yielded inconclusive results. This meta-analysis aims to obtain a more precise estimation of the association between APOE4 allele and prognosis of TBI patients.Methods: A literature search of PubMed, Embase, Web of Science, Cochrane Library, CISCOM, CINAHL, Google Scholar, CNKI and CBM databases was conducted for articles published before July 1st, 2013. Crude odds ratios (OR) with 95% confidence intervals (CI) were calculated. Results: Thirteen cohort studies were included with a total of 662 TBI patients with APOE4 (+) and 1614 TBI patients with APOE4 (-). The meta-analysis results revealed that the APOE4 allele was associated with a poor prognosis in TBI patients (OR=0.68, 95% CI: 0.48-0.96, p=0.027). Subgroup analysis by ethnicity indicated that TBI patients with APOE4 (+) had a worse prognosis than those with APOE4 (-) in Asian populations (OR=0.46, 95% CI: 0.21-0.99, p=0.046), but not in Caucasian populations (OR=0.75, 95% CI: 0.53-1.08, p=0.120). A further subgroup analysis by TBI grade showed that the APOE4 allele was associated with poor prognosis in severe TBI patients (OR=0.43, 95% CI: 0.21-0.87, p=0.020). However, there was no evidence for any association between the APOE4 allele and poor prognosis in patients with other grades of TBI (all p>0.05). Conclusion: The current meta-analysis indicates that the APOE4 allele may be associated with a poor prognosis in severe TBI patients and in Asian populations. The APOE4 allele may be used as a biomarker in predicting the prognosis of TBI patients.