Morquio A syndrome (mucopolysaccharidosis (MPS) IVA; OMIM #253000) is a rare inherited lysosomal storage disorder in which deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulfatase (GALNS, EC 3.1.6.4) causes progressive accumulation of the glycosaminoglycans (GAGs) chondroitin-6-sulfate and keratan sulfate (KS) in tissues and organs. Here, GALNS is linked to mucopolysaccharidosis type 4A.