To evaluate the effect of muscarinic acetylcholine receptor M2 (CHRM2) gene variants on changes in Mayer Wave (MW) amplitude and discordance in recently concussed athletes.

CHRM2 A/A homozygotes have been shown to possess an adverse cardiac autonomic profile compared to other genotypes (i.e., A/T, T/T). A growing body of evidence indicates that a transient cardiac autonomic dysfunction emerges after a concussion.  The baroreflex buffers perturbations to systolic blood pressure (SBP) through changes in efferent discharge to the heart and vasculature.  MWs appear at a frequency of 0.1Hz in the low frequency (LF) band of the heart rate (HR) and SBP power spectrum as a result of the baroreflex.

A prospective study was performed in 12 concussed college-aged athletes (gender: 9 female, 3 male; age: 20±1 years; height: 1.70±0.11 meters; weight: 74±17 kilograms). Cardiovascular autonomic function (i.e., digital electrocardiogram and continuous beat-to-beat SBP) was assessed at rest for 10 minutes in the supine position within 48 hours (48H) of concussion.  A saliva sample was obtained and a commercial laboratory identified the CHRM2 single nucleotide polymorphism (rs8191992) using PMR-array. Fast-Fourier transform was performed and power calculated from HR and SBP components for LF spectra and MW activity. The dependent variables (e.g., MWBP, MWHR) were log₁₀ transformed and a difference score was computed between the MWBP and MWHR (CMW) for each subject.  

A significantly lower CMW (p<0.01) and MWHR (p<0.05) was observed in the CHRM2 A/A [n=7; -3.50(±0.52); 4.51(±0.61)] compared to the A/T [n=3; -2.32(±0.21); 3.13(±0.44]) and T/T [n=2; -2.93(±0.47); 4.67(±0.33)] groups, but not in MWBP.