Congenital disorders of glycosylation is a group of very rare inherited metabolic disorder where defective carbohydrate compounds are attached to glycoproteins and thus impairing glycoprotein function. Type 4 is caused by a genetic defect which involves the gene for a particular enzyme (dolichyl-P-mannose:Man-5-GlcNAc-2-PP-dolichyl-mannosyltransferase).
* Small head * Severe epilepsy * Severely impaired psychomotor development * Vision problems * Skeletal abnormalities * Partial sialic acid deficiency
The association of neurological signs, pigmentary retinitis, cutaneous signs and hepatodigestive signs (cytolysis, fibrosis) is highly suggestive of a CDG syndrome. The diagnosis is based on the demonstration of serum N-glycoprotein glycosylation anomalies (isoelectrofocalization of serum transferrin or Western blot of different serum glycoproteins) and dosage of the responsible cellular (leukocytes or fibroblasts) enzymes, and the search for the corresponding mutations. Congenital galactosemia and fructose intolerance are considered to be secondary CDG syndromes since the serum glycoproteins present the same glycosylation anomalies.