Differential DNA Methylation of the Brain-Derived Neurotrophic Factor Gene is Observed after Pediatric Traumatic Brain Injury Compared with Orthopedic Injury

Pediatric traumatic brain injury (TBI) triggers biological changes that may differ from those observed in non-brain injuries. Brain-derived neurotrophic factor (<i>BDNF</i>) DNA methylation (DNAm) may serve as a novel, dynamic biomarker of the brain's response and help identify TBI-specific epigenetic patterns relevant to later recovery. Therefore, the purpose of this study was to examine whether <i>BDNF</i> DNAm differed between children with TBI and those with orthopedic injury (OI, comparison group) acutely and over time. Data were derived from the Epigenetic Effects on TBI Recovery study, a prospective, longitudinal cohort study conducted at UPMC Children's Hospital of Pittsburgh. Children aged 3-18 years hospitalized at a minimum of overnight for complicated mild-to-severe TBI or OI without head trauma were enrolled. Exclusion criteria included prior hospitalization for TBI, pre-existing neurological or psychiatric conditions, or sensory or motor impairments precluding study participation. Blood samples were collected during hospitalization (mean = 31.6 h post-injury) and at 6 (mean = 216.9 days) and 12 months (mean = 405.9 days) post-injury. The primary outcome variable was DNAm assessed via pyrosequencing at five quality-controlled CpG sites in the <i>BDNF</i> gene (chromosome 11, Genome Reference Consortium Human Build 38 positions 27722033, 27722036, 27722047, 27701612, and 27701614). The primary exposure was injury type (TBI vs. OI), with severity (measured via Glasgow Coma Scale [GCS]) examined as a secondary exposure within the TBI group. Primary covariates included age, sex, and race; secondary covariates included pubertal status, age-adjusted body mass index, non-head injury severity, socioeconomic status, and psychosocial adversity. The final analysis sample included <i>n</i> = 189 participants with TBI and <i>n</i> = 105 participants with OI. Participants were 66.3% male, 83.2% White, and had a mean age of 10.6 (±4.3) years at the time of enrollment. Acutely, children with TBI showed significantly lower DNAm at three of five sites (3.17-5.83% lower; <i>p</i> = 0.0044 to 6.48E-06) while controlling for age, sex, and race. One site remained significantly lower at 12 months (8.56% lower; <i>p</i> = 0.0045); no significant differences were observed at 6 months. Observed differences remained robust across sensitivity models adjusting for secondary covariates. GCS-measured TBI severity was not associated with DNAm at any time point. These findings suggest that <i>BDNF</i> DNAm differs between children with TBI and those with OI, particularly in the acute period. <i>BDNF</i> DNAm differences may reflect early biological responses that are specific to TBI.