CTSA and glycoprotein storage disease: Galactosialidosis is a glycoprotein storage disease caused by an inherited deficiency of the lysosomal protective protein/cathepsin A (PPCA) which is associated in a complex with both, α-neuraminidase (sialidase, NEU1, EC 3.2.1.18) and acid β-galatosidase (β-Gal, EC 3.2.1.23).