MPS IV, also referred to as Morquio syndrome, presents two subtypes: MPS IVA and MPS IVB, caused by the lack of N-acetylgalactosamine-6-sulfate sulfatase (GALNS; MIM 253,000) and β-galactosidase (GLB1; MIM 253,010) respectively. The gene discussed is GALNS; the disease is mucopolysaccharidosis type 4B.