Inborn errors of mannose metabolism discussed in the review are congenital disorders of glycosylation (CDGs) caused by loss of function of three enzymes in the mannose metabolism pathway: mannose phosphate isomerase (MPI, MPI-CDG), phosphomannomutase 2 (PMM2, PMM2-CDG), and ALG11 alpha-1,2-mannosyltransferase (ALG11, ALG11-CDG) (Figure 1). This evidence concerns the gene PMM2 and congenital disorder of glycosylation.