Mild traumatic brain injury (mTBI) results in variable clinical trajectories and outcomes. The source of variability remains unclear, but may involve genetic variations, such as single nucleotide polymorphisms (SNPs). A SNP in catechol-o-methyltransferase (COMT) is suggested to influence development of post-traumatic stress disorder (PTSD), but its role in TBI remains unclear. Here, we utilize the Transforming Research and Clinical Knowledge in Traumatic Brain Injury Pilot (TRACK-TBI Pilot) study to investigate whether the COMT Val¹⁵⁸Met polymorphism is associated with PTSD and global functional outcome as measured by the PTSD Checklist - Civilian Version and Glasgow Outcome Scale Extended (GOSE), respectively. Results in 93 predominately Caucasian subjects with mTBI show that the COMT Met¹⁵⁸ allele is associated with lower incidence of PTSD (univariate odds ratio (OR) of 0.25, 95% CI [0.09-0.69]) and higher GOSE scores (univariate OR 2.87, 95% CI [1.20-6.86]) 6-months following injury. The COMT Val¹⁵⁸Met genotype and PTSD association persists after controlling for race (multivariable OR of 0.29, 95% CI [0.10-0.83]) and pre-existing psychiatric disorders/substance abuse (multivariable OR of 0.32, 95% CI [0.11-0.97]). PTSD emerged as a strong predictor of poorer outcome on GOSE (multivariable OR 0.09, 95% CI [0.03-0.26]), which persists after controlling for age, GCS, and race. When accounting for PTSD in multivariable analysis, the association of COMT genotype and GOSE did not remain significant (multivariable OR 1.73, 95% CI [0.69-4.35]). Whether COMT genotype indirectly influences global functional outcome through PTSD remains to be determined and larger studies in more diverse populations are needed to confirm these findings.

Background

Brain volumes in regions such as the hippocampus and amygdala have been associated with risk for the development of posttraumatic stress disorder (PTSD). The objective of this study was to determine whether a set of regional brain volumes, measured by magnetic resonance imaging at 2 weeks following mild traumatic brain injury, were predictive of PTSD at 3 and 6 months after injury.

Methods

Using data from TRACK-TBI (Transforming Research and Clinical Knowledge in TBI), we included patients (N = 421) with Glasgow Coma Scale scores 13-15 assessed after evaluation in the emergency department and at 2 weeks, 3 months, and 6 months after injury. Probable PTSD diagnosis (PTSD Checklist for DSM-5 score, ≥33) was the outcome. FreeSurfer 6.0 was used to perform volumetric analysis of three-dimensional T1-weighted magnetic resonance images at 3T obtained 2 weeks post injury. Brain regions selected a priori for volumetric analyses were insula, hippocampus, amygdala, superior frontal cortex, rostral and caudal anterior cingulate, and lateral and medial orbitofrontal cortices.

Results

Overall, 77 (18.3%) and 70 (16.6%) patients had probable PTSD at 3 and 6 months. A composite volume derived as the first principal component incorporating 73.8% of the variance in insula, superior frontal cortex, and rostral and caudal cingulate contributed to the prediction of 3-month (but not 6-month) PTSD in multivariable models incorporating other established risk factors.

Conclusions

Results, while needing replication, provide support for a brain reserve hypothesis of PTSD and proof of principle for how prediction of at-risk individuals might be accomplished to enhance prognostic accuracy and enrich clinical prevention trials for individuals at the highest risk of PTSD following mild traumatic brain injury.