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Mucopolysaccharides, also known as glycosaminoglycans (GAGs), are long, unbranched polysaccharides composed of repeating disaccharide units. Each disaccharide typically contains an amino sugar (such as N-acetylglucosamine or N-acetylgalactosamine) and an uronic sugar (such as glucuronic or iduronic acid). Many GAGs are sulfated, imparting a negative charge that attracts water and cations.

A common structural theme is that GAGs are often covalently linked to a protein core to form proteoglycans, which are major components of the extracellular matrix and cell surfaces. Hyaluronic acid is a non-sulfated GAG that exists independently of a core protein. GAGs contribute to tissue hydration, resilience, and elasticity and modulate cell signaling and matrix organization.

Biogenesis and degradation: GAGs are synthesized in the Golgi apparatus and attached to core proteins in the secretion pathway. Degradation occurs in lysosomes through specific hydrolases. Impaired breakdown leads to accumulation of GAGs in lysosomes, a hallmark of mucopolysaccharidoses.

Clinical relevance: Mucopolysaccharidoses are a group of inherited lysosomal storage disorders caused by deficiencies of enzymes required to degrade GAGs. They present with variable features, including skeletal abnormalities, organomegaly, and developmental delay. Diagnosis combines urinary GAG testing, enzyme activity assays, and genetic testing. Treatment options for some forms include enzyme replacement therapy and hematopoietic stem cell transplantation, aiming to reduce GAG storage and improve outcomes.

See also: glycosaminoglycan, proteoglycan, mucopolysaccharidosis.