CSTB and progressive myoclonus epilepsy: In NCLs, EPM2 and sialidosis, neurodegeneration is caused by gene deficiency with accumulation of intracellular inclusion bodies (Haltia, 2003; Verhalen et al., 2018; Khan and Sergi, 2018), whereas in EPM1-PME, it is caused by a loss of function of the cystatin B gene, which is an inhibitor of cysteine protease, therefore the resulting symptoms are attributed to excessive proteolysis (Turk and Bode, 1991).