The lysosomal disorder galactosialidosis (GS) results from a mutation in the CTSA gene and from deficiency in the lysosomal carboxypeptidase protective protein/cathepsin A (PPCA) [57], leading to insufficient β-galactosidase (β-Gal) and N-acetyl-α-neuraminidase (NEU1) activities [58]. Here, CTSA is linked to Gerstmann syndrome.