MAPT and young-onset Parkinson disease: Since post-concussive increase of CSF t-tau augments with age (Taghdiri et al. 2019), and CSF t-tau levels could be higher in LOPD than in YOPD patients (Schirinzi et al. 2020b), we may presume that HTs contribute to YOPD by precipitating the genetic vulnerability through mechanisms different from tau-mediation.