MAPT and amyotrophic lateral sclerosis: To determine the diagnostic and prognostic significance of neurofilament light chain (NfL), TAR DNA‐binding protein 43 (TDP‐43), and total tau (t‐tau) in cerebrospinal fluid (CSF) and plasma of patients with amyotrophic lateral sclerosis (ALS) and to investigate whether the combined use of those biomarker candidates can improve their diagnostic performance.