NEU1 and sialidosis type 2: Sialidosis or mucolipidosis I (OMIM# 256550) and galactosialidosis (GS, OMIM# 256540) are two related disorders belonging to the glycoproteinosis subgroup of over 70 other lysosomal storage diseases.1 Sialidosis is a recessive disease resulting from mutations in the NEU1 gene, which encodes neuraminidase 1 (NEU1).