GALNS and mucopolysaccharidosis type 4A: Mucopolysaccharidosis (MPS) IVA (Morquio A syndrome, OMIM #253000) is an autosomal recessive lysosomal storage disorder caused by a mutation in GALNS, which encodes the enzyme N-acetylgalactosamine-6-sulfatase (EC 3.1.6.4, GALNS) [1].