We previously identified apical dendrite defects in UMNs that become diseased by mSOD1 toxicity,37, 57 lack of Alsin function,116 Profilin defects,117 and TDP‐43 pathology,32 and these cellular defects were fully recapitulated in the Betz cells—the UMNs in humans—of a broad spectrum of ALS patients, including sALS, fALS, as well as ALS/FTLD.8 Here, ALS2 is linked to amyotrophic lateral sclerosis.