N-METHYL-D-ASPARTIC ACID RECEPTOR SUBUNIT NR2A REPEAT

Abstract

During a concussion, mechanical forces cause neuron cell strain that initiates dysfunction through the indiscriminate movement of ions through protein channels. Extracellular glutamate binds with cell membrane proteins (e.g. NR2A), which exacerbates the Ca2+ ion influx and prolongs neuron dysfunction. Genetic variation may be a factor in regulating glutamate binding and therefore cell recovery time. The NR2A subunit of NMDA contains a variable (GT)n nucleotide tandem repeat (VNTR) within GRIN2A promoter region. This VNTR has been shown to regulate transcription levels in a length dependent manner, where longer repeat decreases transcription of the NR2A subunit. The purpose of this study was to determine the association of the GRIN2A VNTR and recovery (days) as well as concussion severity scores within concussed athletes. The independent variable was VNTR (long allele vs. short allele). The primary dependent variable, recovery time, was defined as injury date to return to play (RTP) clearance date as determined by the physician. Participant RTP time was categorized as normal ( 20 days). Secondary dependent variables were assessed at the initial evaluation and included vestibular ocular score, Balance Error Scoring System (BESS) score, and Immediate Post Concussion and Cognitive Testing (ImPACT) module scores. All 51 participants were athletes, comprised of 38 males and 13 females with a mean age of 18.69  6.65. Participants were evaluated at a university concussion center. The standardized concussion evaluation consisted of cranial nerve, vestibular ocular tests, balance (Balance Error Scoring System), signs and symptoms (s/s), and neurocognitive (ImPACT) testing. Each participant was genotyped via saliva sample for the GRIN2A (GT)n repeat polymorphism (rs3219790). Data analysis consisted of descriptive and inferential statistics. Chi-squares were used to assess the association between VNTR (long allele versus short allele) and concussion recovery (prolonged versus normal). Regression analyses were used to estimate extent to which non-genetic factors and genotype contributed to concussion recovery group assignment. One-way ANOVAs were used to identify any significant differences in vestibular ocular, BESS, and ImPACT module scores between long and short alleles. Primary potential non-genetic contributing factors were age, race, sex, concussion history, dizziness at time of injury, history of migraines, and history of ADHD. The alpha level was set at p ≤ .05. There were no differences between demographic or health history within the VNTR or recovery groups. There was a significant association (x2 = 4.01, p = 0.045) between the VNTR group (dominant model: LL versus SS + LS) and recovery, where the chance of prolonged recovery was 4.3 times greater for carriers of the homozygous long allele. There were no differences in concussion severity scores between VNTR group and concussion severity scores. This was the first study to investigate the association of the (GT)n VNTR within GRIN2A. We established a DNA collection, estimation, and genotyping protocol of the (GT)n VNTR for 96 samples and demonstrated accuracy of this genotyping method. Clinically, athletes carrying the long allele genotype may be predisposed to prolonged recovery following a concussive injury.