GALNS and mucopolysaccharidosis type 4A: Mucopolysaccharidosis IVA (MPS IVA; OMIM 253000, Morquio A disease) is an autosomal recessive disorder caused by a deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulfatase (GALNS, EC 3.1.6.4), which catalyzes a step in the catabolism of glycosaminoglycans (GAGs), keratan sulfate (KS) and chondroitin-6-sulfate (C6S).