PMM2, also known as Phosphomannomutase 2, belongs to the eukaryotic PMM family. PMM2 is involved in the synthesis of the GDP-mannose and dolichol-phosphate-mannose required for a number of critical mannosyl transfer reactions. It catalyzes the isomerization of mannose 6-phosphate to mannose 1-phosphate. Mutations in PMM2 are associated with Congenital disorders of glycosylation (CDG)-Ia, an autosomal recessive disorder characterized by central nervous system dysfunction and multiorgan failure.