Test ID: IDST
Alpha-L-Iduronidase, Fibroblasts

Diagnosis of mucopolysaccharidosis I (MPS I), Hurler syndrome (MPS IH), MPS IS (Scheie syndrome (MPS IS), and Hurler-Scheie syndrome (MPS IH/S)

Diagnostic testing. Not recommended for carrier detection.

Fibroblasts are the preferred specimen since testing for other mucopolysaccharide storage diseases may be necessary.

When this test is ordered, a fibroblast culture and cryopreservation for biochemical studies will always be performed at an additional charge. However, for multiple lysosomal enzyme assays on a patient utilizing fibroblast culture, only 1 culture is required regardless of the number of enzyme assays ordered. If viable cells are not obtained within 10 days, client will be notified.

• Informed Consent for Genetic Testing

IDST/8780: Fluorometric Enzyme Assay

CRYOB/88832: Fibroblast Subculture Followed by Cryopreservation and Storage

This test is not recommended for prenatal testing.

Forms:

1.   1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.

2.   2. If not ordering electronically, submit a Biochemical Genetics Request Form (Supply T439) with the specimen.

Submit only 1 of the following specimens:

Specimen Type: Cultured fibroblasts

Container/Tube: T-75 or T-25 flask

Specimen Volume: 1 full T-75 flask or 2 full T-25 flasks

Specimen Stability Information: Ambient (preferred)/Refrigerated <24 hours

Specimen Type: Skin biopsy

Container/Tube: Sterile container with any standard cell culture media (eg, minimal essential media, RPMI 1640). The solution should be supplemented with 1% penicillin and streptomycin. Tubes can be supplied upon request (Eagle's minimum essential medium with 1% penicillin and streptomycin [Supply T115]).

Specimen Volume: 4-mm punch

Specimen Stability Information: Refrigerated (preferred)/Ambient

The mucopolysaccharidoses are a group of lysosomal storage disorders caused by the deficiency of any of the enzymes involved in the stepwise degradation of glycosaminoglycans (GAG). Accumulation of GAG (previously called mucopolysaccharides) in lysosomes interferes with normal functioning of cells, tissues, and organs.

Mucopolysaccharidosis I (MPS I) is an autosomal recessive disorder caused by a reduced or absent activity of the alpha-L-iduronidase enzyme. Deficiency of the alpha-L-iduronidase enzyme can result in a wide range of phenotypes further categorized into 3 syndromes: MPS IH (Hurler syndrome), MPS IS (Scheie syndrome), and MPS IH/S (Hurler-Scheie syndrome). 

Clinical features and severity of symptoms of MPS I are widely variable, ranging from severe disease to an attenuated form that generally presents at a later onset with a milder clinical presentation. Symptoms typically include coarse facies, progressive dysostosis multiplex, hepatosplenomegaly, corneal clouding, hearing loss, mental retardation or learning difficulties, and cardiac valvular disease. The incidence of MPS I is approximately 1 in 100,000 live births. Treatment options include hematopoietic stem cell transplantation and enzyme replacement therapy.

A diagnostic workup in an individual with MPS I typically demonstrates elevated levels of urinary GAG and increased amounts of both dermatan and heparan sulfate detected on thin-layer chromatography. Reduced or absent activity of alpha L-iduronidase is diagnostic of MPS I; however, enzymatic testing is not reliable to detect carriers. Molecular sequence analysis of the IDUA gene allows for detection of the disease-causing mutation in affected patients and subsequent carrier detection in relatives. Currently, no clear genotype-phenotype correlations have been established.

0.44-1.04 U/g of cellular protein

Mucopolysaccharidosis I is characterized by very low or absent activity of alpha-L-iduronidase; differentiation between Hurler syndrome (MPS IH), MPS IS (Scheie syndrome (MPS IS), and Hurler-Scheie syndrome (MPS IH/S) is based on clinical findings.

This test cannot reliably determine carrier status for mucopolysaccharidosis I (MPS I).

The presence of a pseudodeficiency allele may cause reduced activity of alpha-L-iduronidase with the use of artificial substrate, which is used in this assay. This can result in values below the normal reference range, but will typically be greater than levels found in patients with MPS I.

Interfering factors include lack of viable cells, bacterial contamination, failure to transport tissue in an appropriate media, excessive transport time, and exposure of the specimen to temperature extremes (freezing or >30 degrees C).

1. Martins AM, Dualibi AP, Norato D, et al: Guidelines for the management of mucopolysaccharidosis type I. J Pediatr 2009 Oct:155(4 Suppl):S32-S46

2. Neufeld EF, Muenzer J: The mucopolysaccharidoses. In The Metabolic and Molecular Basis of Inherited Disease. Vol 3. Eighth edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company, 2001, pp 3427-3435

Incubation of 4-methylumbelliferyl alpha-L-iduronide with whole-cell homogenates prepared from cultured skin fibroblasts yields 4-methylumbelliferone, which is fluorometrically measured. The inclusion of inhibitor of glucuronidase is necessary because the iduronide substrate is not 100% pure and contains some 4-methylumbelliferyl glucuronide. (Hopwood JJ, Muller V, Smithson A, Baggett N: A fluorometric assay using 4-methylumbelliferyl alpha-L-iduronide for the estimation of alpha-L-iduronidase activity and the detection of Hurler and Scheie syndromes. Clin Chim Acta 1979;92:257-265)

Varies

82657-Alpha-L-iduronidase

88233-Fibroblast culture

88240-Cryopreservation for biochemical studies