Mucopolysaccharidosis IVA (MPS IVA, Morquio A disease, OMIM 253000) is a rare autosomal-recessive disease characterized by the deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS, EC 3.1.6.4) with an estimated incidence of 1:200,000 born alive1, 2. The gene discussed is GALNS; the disease is mucopolysaccharidosis type 4.