NEU1 and sialidosis: This finding is crucial as it indicates that NEU1 mutations affecting its activity may exist in the absence of characteristic features of sialidosis (Chen et al., 2006; Canafoglia et al., 2014; d’Azzo et al., 2015; Muona et al., 2015; Mohammad et al., 2018; Bou Ghannam et al., 2019).