The current finding of a positive correlation between exosome size and t-tau, as well as a negative correlation between exosome size and RBP-4, provides a rationale for exploring the prophylactic clinical use for concussion based on a new class of retinoid receptor modulators (RAR-Ms), exemplified by Ellorarxine, currently MHRA approved to proceed to clinical trials for ALS (www.nevrargenics.com). The gene discussed is RBP4; the disease is amyotrophic lateral sclerosis.