Mucopolysaccharidosis IVA (MPS IVA, Morquio A syndrome) is a rare lysosomal storage disorder caused by mutations in the GALNS gene, resulting in N-acetylgalactosamine-6-sulfatase (GALNS) deficiency and accumulation of keratan sulfate and chondroitin-6-sulfate. Here, GALNS is linked to mucopolysaccharidosis type 4A.