TARDBP and amyotrophic lateral sclerosis: In a separate biomarker validation cohort of ante-mortem skin biopsies taken from people who went on to develop ALS, we establish skin TDP-43 pathology as a potential pre-symptomatic ALS biomarker, occurring at very high incidences, across a wide-range of anatomical sites, from up to 26.5 years prior to ALS symptom onset.