Carbohydrate-deficient glycoprotein syndromes: inborn errors of protein glycosylation

The carbohydrate-deficient glycoprotein (CDG) syndromes (CDGS) are a series of autosomal recessive enzyme deficiencies which result in incomplete glyc osylation of plasma proteins. CDGS types Ia and Ib have been related to def iciencies of phosphomannomutase and phosphomannose isomerase, respectively, while CDGS type II results from a deficiency of N-acetylglucosaminyltransf erase II. Secondary CDG syndromes are associated with galactosaemia and her editary fructose intolerance. The diagnosis of CDGS is most easily made by studying the glycoforms of suitable marker proteins using either electropho resis or isoelectric focusing. This paper reviews the structure of the glyc an chains of proteins and structural alterations in CDGS. It also outlines analytical techniques which are useful in the laboratory study of protein g lycoforms and the diagnosis of CDGS.