A 6-year-old boy

presents with special symptoms – joint stiffness, corneal opacity, heart valve abnormality,

and worsening hearing impairment. After a complex diagnosis, the final is the type I mucopolysaccharidosis. Mucopolysaccharidoses are

hereditary disorders of the activity of lysosomal enzymes, whose role in a

healthy organism is the natural breakdown of glycosaminoglycans

(mucopolysaccharides). During these diseases, glycosaminoglycans accumulate

inside these lysosomes. What are glycosaminoglycans?