AIM: We investigated serum DNA methylation patterns in genomic repetitive 
elements, LINE-1 and Alu, for post-traumatic stress disorder (PTSD) cases and 
controls who were US military service members recently deployed to Afghanistan 
or Iraq.
METHODS: Cases (n = 75) had a postdeployment diagnosis of PTSD. Controls (n = 
75) were randomly selected service members with no postdeployment PTSD 
diagnosis. Pre- and post-deployment sera were accessed, DNA was extracted and 
DNA methylation (percentage 5-methyl cytosine) was quantified via 
pyrosequencing. Conditional and unconditional logistic regressions were used to 
compare: cases post- to pre-deployment; controls post- to pre-deployment; cases 
to controls predeployment; cases to controls postdeployment.
RESULTS: LINE-1 was hypermethylated in controls post- versus pre-deployment 
(odds ratio [OR]: 1.33; 95% CI: 1.06-1.65) and hypomethylated in cases versus 
controls postdeployment (OR: 0.82; 95% CI: 0.67-1.01). Alu was hypermethylated 
for cases versus controls predeployment (OR: 1.46; 95% CI: 1.08-1.97).
CONCLUSION: Patterns of hypermethylation of LINE-1 in controls postdeployment 
and of Alu in cases postdeployment are intriguing and may suggest resilience or 
vulnerability factors.