Glycosaminoglycans and Mucopolysaccharidoses

Key points

• • Glycosaminoglycans (GAGs) are long chains of repeating sugar units; most are covalently linked to a core protein to form proteoglycans (hyaluronic acid is an exception), and they hold water and cushion tissues.
• • They are a major part of the jelly-like ground substance of connective tissue and of cartilage, where they resist compression.
• • Examples include hyaluronic acid (in joint fluid and the eye), chondroitin sulfate (in cartilage) and heparin (stored in mast cells and used pharmacologically as an anticoagulant).
• • Heparan sulfate and others sit on cell surfaces and in basement membranes, where they help cells stick together and signal.
• • The mucopolysaccharidoses are inherited diseases in which a missing enzyme lets GAGs build up in the lysosomes, damaging many organs.
• • Hurler syndrome causes coarse facial features, an enlarged liver and spleen, clouding of the cornea and learning difficulty; Hunter syndrome is an X-linked form in which corneal clouding is typically absent, an important distinguishing feature, though its severity varies.