Mucopolysaccharidoses are caused by defective breakdown of glycosaminoglycans (GAGs)

What are these glycosaminoglycans? They are huge molecules, they are really macromolecules. This is on the electron microscopy, where these proteins can be seen.  It is a protein core with all kinds of long disaccharide molecules  attached to this protein. So this is a protein glycan and these parts are the true glycosaminoglycans.