Urinary GAG testing

The level of urinary glycosaminoglycans (GAGs) is increased in patients with any MPS syndrome, so detection of excessive urinary GAGs is usually the first diagnostic indicator (unless a strong family history allows this stage to be bypassed).1,2

Urine samples should be analyzed via chromatography or electrophoresis to identify abnormal GAG patterns even if their levels are not elevated.1 A negative GAG test does not necessarily rule out Hunter syndrome (MPS II) as a diagnosis.1,2

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Enzyme testing

Testing for absent or very low iduronate-2-sulfatase (I2S) activity is diagnostic for Hunter syndrome. Enzyme activity can be measured in cultured fibroblasts, leukocytes, plasma or serum, or dried blood spots.1,2

Second sulfatase testing

A second sulfatase should be measured to rule out multiple sulfatase deficiency, and confirm the diagnosis of Hunter syndrome. 1,2

Genetic testing

Over 330 alterations in the I2S gene have been reported in Hunter syndrome patients. Once a likely disease-causing mutation has been identified, all family members may be tested to identify carriers or those at risk, and counseling should be provided.1,2

Suspect? Refer.

If you suspect Hunter syndrome, refer your patient to a medical geneticist for an accurate diagnosis.

References:  1. Burton BK, Giugliani R Eur J Pediatr 2012; 171(4): 631–639.  2. Scarpa M et al. Orphanet J Rare Dis 2011; 6: 72.

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