GALNS and mucopolysaccharidosis type 4A: Mucopolysaccharidosis (MPS) IVA, also known as Morquio A syndrome (OMIM #253000), is a rare, inherited lysosomal storage disorder in which deficient activity of the enzyme N-acetylgalactosamine-6-sulfatase (GALNS; EC: 3.1.6.4) causes accumulation of the glycosaminoglycans keratan sulfate and chondroitin-6-sulfate in multiple tissues and organs [1–4].