Prion disease exhibits a more dramatic elevation of NfL than that seen in perhaps any other neurological disorder.24-26 We and others have followed pre-symptomatic people at risk for genetic prion disease, however, and have found that plasma NfL increases in only a brief window prior to the onset of symptom,26-29 consistent with the rapid clinical course of prion disease.30 Here, we observed an NfL increase of 3.5-fold in plasma and 5.7-fold in CSF in an asymptomatic individual at risk for genetic prion disease following 6 weeks’ treatment with oral minocycline for a dermatologic indication. The gene discussed is NEFL; the disease is nervous system disorder.