Pathophysiology

The mucopolysaccharidoses are lysosomal storage disorders due to a lack of enzymes that normally degrade glycosaminoglycans. They are characterized by the intracellular accumulation and urinary excretion of glycosaminoglycans (i.e., mucopolysaccharides). The seven types of mucopolysaccharidoses are each distinguished by an excess of a particular urinary mucopolysaccharide.74

Clinical presentation

Inheritance is autosomal dominant, except for type II, which is x-linked.

Clinical features vary but generally include a characteristic coarse facies (i.e., thickened lips and open mouth), short height, bony abnormalities, mental retardation, corneal opacities, and hepatosplenomegaly.

Type III (Sanfilippo's syndrome) is the most common mucopolysaccharidosis. It has four subtypes. The onset of symptoms is usually after 2 years of age, followed by rapidly progressive neurologic and cognitive deterioration. Seizures occur in nearly half of patients.

Evaluation

The EEG shows nonspecific abnormalities, and neuroimaging studies reveal cortical atrophy and ventricular dilatation.

Laboratory studies confirm abnormalities on urine screening tests for glycosaminoglycans. Sophisticated cell culture or serum assays are available to evaluate patients for specific enzyme deficiencies.

Treatment

Treatment is symptomatic. Enzyme replacement by bone marrow transplantation has produced systemic improvement in selected patients but has not prevented neurologic deterioration.

Adapted from: Schachter SC and Lopez MR. Metabolic disorders. In: Ettinger AB and Devinsky O, eds. Managing epilepsy and co-existing disorders. Boston: Butterworth-Heinemann; 2002;195–208. 
With permission from Elsevier (www.elsevier.com). 

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Reviewed By: 
Steven C. Schachter, MD
on: 
Wednesday, March 31, 2004