Hurler Syndrome (MPS I): Alpha-iduronidase Enzyme Analysis

Test Information

This biochemical test is a quantitative measurement of of alpha-iduronidase enzyme activity can be used as a 1st tier test for patients with a clinical suspicion of Mucopolysaccharidosis I (MPS I)/Hurler Syndrome. Demonstration of deficient alpha-iduronidase enzyme activity is considered the gold standard to confirm a diagnosis of Mucopolysaccharidosis I (MPS I)/Hurler Syndrome.

Turnaround Time

2 weeks

CPT Code(s)






Clinical Information

Mucopolysaccharidosis type I (MPSI) is caused by deficient alpha-iduronidase enzyme activity, which results in an accumulation of the glycoamnioglycan heparan sulfate and dermatan sulfate in body tissues. MPS I is a multisystem progressive disorder demonstrating wide phenotypic variability with three different MPSI subtypes described (Hurler, Hurler-Scheie, and Scheie). Hurler syndrome is considered the more severe end of the phenotypic spectrum with patients generally diagnosed before 18 months of age while Hurler-Scheie and Scheie syndromes are usually used to describe the milder phenotypes. These less severe cases, also known as attenuated MPS I, will often present between 3 and 10 years of age. Clinical features of MPS I include coarse facial features, dysostosis multiplex, short stature, hirsutism, cloudy corneas, and hepatosplenomegaly, and cardiac comlications. Developmental delay and intellectual disability is more severe in those patients with Hurler syndrome and is a distinguishing feature between the subtypes of MPS I.


This test can be used to confirm a suspected Hurler syndrome diagnosis


4-methylumbelliferyl substrate

Specimen Requirements

Enzyme activity can be measured in leukocytes, plasma, cultured fibroblasts, or dried blood spots. For leukocytes or plasma, please send 5-10 ml of whole blood in a green top (sodium heparin) tube. Plasma can also be removed from spun down sample and sent frozen. For dried blood spot collection, a minimum of three circles need to be filled in. Each circle should contain one drop of blood (about 100 microliters). See the link below for additional sample collection and handling instructions.

Transport Instructions

Whole blood should be sent over overnight at ambient temperature. Plamsa can be removed once the sample has been drawn and sent frozen on dry ice. Do not freeze whole blood. For a dried blood spot: When the sample has dried 3-4 hours, fold cover at score line, over sample, and tuck into flap. Samples can be mailed at ambient temperature.

Have Questions? Need Support?

Call our laboratory at 1-800-473-9411 or contact one of our Laboratory Genetic Counselors for assistance.
Robin Fletcher, MS, CGC
Falecia Thomas, MS, CGC
Alex Finley, MS, CGC

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