GALNS and mucopolysaccharidosis type 4A: Mucopolysaccharidosis IVA (MPS IVA, Morquio syndrome A, OMIM #253000) is a rare genetic disease caused by impaired N-acetylgalactosamine-6-sulfatase (GALNS, E.C.3.1.6.4) activity, which led to the lysosomal accumulation of keratan sulfate (KS) and chondroitin 6-sulfate (C6S)1,2.