GALNS and mucopolysaccharidosis type 4A: Morquio A syndrome, or mucopolysaccharidosis IVA (MPS IVA), is an autosomal recessive lysosomal storage disorder caused by defective activity of N-acetyl-galactosamine-6-sulfatase (GALNS), an enzyme that catabolizes the glycosaminoglycans keratan sulfate and chondroitin-6-sulfate.