AbstractThe mucopolysaccharidoses (MPS) are a group of rare, inherited lysosomal storage disorders of glycosaminoglycan (GAG) catabolism: chondroitin sulphate, dermatan sulphate, heparan sulphate, keratan sulphate, hyaluronan. The GAG accumulation results in progressive cellular damage in multiple organ systems. MPS are multisystemic progressive diseases leading to reduced life expectancy. MPS disorders are inherited in an autosomal recessive pattern, except for MPSII, that is an X-linked recessive disease. There seven different MPS disorders caused by deficiency in the activity of a single lysosomal enzyme required for GAG degradation. For each MPS, there is a continuum spectrum of clinical presentation from severe to attenuated forms. Clinical manifestations include dysmorphia, dysostosis multiplex, joint stiffness, growth impairment, hepato-splenomegaly, cognitive involvement in the severe forms, hearing loss, ocular abnormalities (corneal clouding, retinopathy, optic atrophy). Cardiac and respiratory impairment. There are two treatment options for patients with MPS that are directed at the underlying pathophysiology: haematopoietic stem cell transplantation, which is useful for selected patients, and recombinant enzyme replacement therapy, which is available for MPS I, II, IV, VI and VII. Early diagnosis and treatment can improve patient outcomes and may reduce the disease burden on patients and caregivers.The oligosaccharidoses are a group of exceedingly rare lysosomal storage diseases that affect oligosaccharides (= glycoprotein) catabolism.