Despite this clinical heterogeneity, a unifying pathological feature seen in the majority of ALS and FTD patients is the presence of the 43 kDa Tar‐DNA binding protein (TDP‐43), whose pathological misfolding and accumulation is observed in the brains and spinal cord of the majority of ALS patients with the notable exception of ALS cases caused by SOD1 mutation 4. This evidence concerns the gene SOD1 and amyotrophic lateral sclerosis.