TARDBP and amyotrophic lateral sclerosis: A further complicating factor in the interpretation of many of these studies is the need to account for the neurotoxicity not only of the full length TDP-43 protein, which could retain functional activity, but also of the non-functional N-terminally truncated 25 kDa fragment of TDP-43 that is found specifically in the brains of patients affected with ALS and FTLD-U [3].