Galactosialidosis (GS, OMIM #256540) is a rare metabolic disorder resulting from mutations in the protective protein/cathepsin A (PPCA) or CTSA gene, which is characterized by malfunction of the lysosomal glycoprotein degradation and subsequent intra-lysosomal accumulation of sialyloligosaccharides and glycopeptides. The gene discussed is CTSA; the disease is metabolic disease.