When calpain, 150/145 kDa α-fodrin and calpastatin were analyzed in protein extracts of 6 days differentiated MNs, we observed the following results: (i) 150/145 kDa α-fodrin degradation product was significantly increased in SMA samples (1.29 ± 0.10, p = 0.0278) compared to the Control condition; (ii) calpain protein level was significantly reduced in SMA samples (0.68 ± 0.06, p = 0.0010) compared to the Control condition; and (iii) calpastatin protein levels were not significantly different between SMA and Control conditions (p = 0.720) (Fig. 3c). Here, CAST is linked to proximal spinal muscular atrophy.