Inborn errors of glycosylation or other specified protein modification

**Definition:** Congenital Disorders of Glycosylation (CDG) syndromes are a group of glycoprotein synthesis disorders characterised by neurological manifestations that can be associated with multivisceral involvement. The CDG syndromes are associated with different enzymatic deficits.

**Long definition:** Carbohydrate-deficient glycoprotein (CDG) syndromes are a group of glycoprotein synthesis disorders characterized by neurological manifestations that can be associated with multivisceral involvement. The frequency is estimated to be between 1/50,000 and 1/100,000. The CDG syndromes are associated with different enzymatic deficits of which the most common, CDG Ia, results from a deficit in phosphomannomutase and represents 70% of CDG cases. Psychomotor retardation is the most constant sign. Other more variable signs include lipocutaneous abnormalities (peau d'orange), olivopontocerebellar atrophy, skeletal anomalies, inverted nipples, coagulation disorders, and hepatic cytolysis and fibrosis. The biological diagnosis is based on the demonstration of abnormal glycosylation of serum glycoproteins, measurement of leukocyte enzyme activities and the search for mutations in the corresponding genes. Prenatal diagnosis of CDG syndrome is feasible once the diagnosis has been confirmed in an index case.