GALNS and mucopolysaccharidosis type 4A: Mucopolysaccharidosis (MPS) IVA (OMIM: 253000) is a genetic lysosomal storage disease (LSD) caused by a deficiency in the N-acetylgalactosamine-6-sulfatase (GALNS) enzyme that leads to the lysosomal accumulation of the glycosaminoglycans (GAGs) keratan sulfate (KS) and chondroitin 6-sulfate (C6S) [1,2,3,4,5,6].