A new doctor at the Department of Paediatrics

and Inherited Metabolic Disorders gets acquainted with very rare syndromes. He

did not learn much about them in medical school, and because of their rarity,

they are mainly dealt with only by this department. These include rare

congenital disorders of glycosylation. These are diseases whose cause lies in

defects in the enzymes involved in the synthesis of the oligosaccharide chains

of glycoproteins. Glycoproteins are proteins that have oligosaccharide chains

covalently linked to a central protein chain. It is one of the

post-translational modifications of proteins. Most types of these diseases are

associated with neurological disorders, growth retardation, blood clotting

disorders, liver and gastrointestinal tract disease and typically manifest in

the neonatal or infant period. Where do these post-translational modifications

of proteins within the cell most commonly occur?