S100B and spinal muscular atrophy, type 1: In this study, we performed a follow‐up study of 26 spinal muscular atrophy types 1–3 patients treated with nusinersen between 2017 and 2021 to determine if measured concentrations of total tau, neurofilament light chain, and S100B proteins in cerebrospinal fluid correlate with the duration of nusinersen treatment and with scores obtained using functional scales of motor abilities.