Galactosialidosis (GS, OMIM #256540) is an autosomal recessive lysosomal storage disorder (LSD) caused by a primary defect of protective protein/cathepsin A (PPCA) and/or a secondary defect of components of the lysosomal multienzyme complex (LMC), which includes the two glycosidases, β-galactosidase (β-Gal) and neuraminidase-1 (NEU1)1,2. The gene discussed is CTSA; the disease is lysosomal storage disease.