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Test ID: I2SW Iduronate-2-Sulfatase, Blood

Useful For

Diagnosis of mucopolysaccharidosis II (MPS II, Hunter syndrome) in whole blood specimens

 

This test is not useful for determining carrier status for MPS II.

Reporting Name

Iduronate-2-sulfatase, B

Specimen Type

Whole blood


Necessary Information


Provide a reason for testing with each specimen.



Specimen Required


Container/Tube:

Preferred: Lavender top (EDTA)

Acceptable: Yellow top (ACD)

Specimen Volume: 2 mL


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole blood Ambient (preferred) 7 days
  Refrigerated  7 days

Clinical Information

The mucopolysaccharidoses are a group of disorders caused by the deficiency of any of the enzymes involved in the stepwise degradation of dermatan sulfate, heparan sulfate, keratan sulfate, or chondroitin sulfate, also known as glycosaminoglycans (GAG). Accumulation of GAG in the lysosomes interferes with normal functioning of cells, tissues, and organs. Mucopolysaccharidosis II (MPS II, Hunter syndrome) is an X-linked lysosomal storage disorder caused by the deficiency of iduronate sulfatase (IDS) enzyme and gives rise to the physical manifestations of the disease.

 

Clinical features and severity of symptoms are widely variable ranging from severe infantile onset disease to an attenuated form, which generally has a later onset with a milder clinical presentation. Symptoms may include coarse facies, short stature, enlarged liver and spleen, hoarse voice, stiff joints, cardiac disease, and profound neurologic involvement leading to developmental delays and regression. As an X-linked disorder, MPS II occurs primarily in male patients with an estimated incidence of 1 in 120,000 male births, although symptomatic carrier females have been reported. Treatment availability, including hematopoietic stem cell transplantation and enzyme replacement therapy, makes early diagnosis desirable, as early initiation of treatment has been shown to improve clinical outcomes. Newborn screening for MPS II has been implemented in some states.

 

A diagnostic workup in an individual with MPS II typically demonstrates elevated levels of urinary GAG and increased amounts of both dermatan sulfate and heparan sulfate (see MPSQU / Mucopolysaccharides Quantitative, Random, Urine and MPSBS / Mucopolysaccharides, Blood Spot). Reduced or absent activity of IDS can confirm a diagnosis of MPS II but may also be deficient in individuals with multiple sulfatase deficiency. Enzymatic testing is not reliable to detect carriers. Molecular genetic testing of the IDS gene allows for detection of the disease-causing variant in affected individuals and subsequent carrier detection in female relatives (see MPS2Z / Hunter Syndrome, Full Gene Analysis, Varies). Currently, no clear genotype-phenotype correlations have been established.(1)

Reference Values

≥1.5 nmol/hour/mL

Interpretation

Specimens with results below 1.5 nmol/hour/mL in properly submitted specimens are consistent with iduronate-2-sulfatase deficiency (mucopolysaccharidosis II: MPS II). If clinically indicated, consider further confirmation by molecular genetic analysis of the IDS gene. Note that this enzyme's activity can also be reduced in multiple sulfatase deficiency (MSD).(2) If clinically indicated, consider biochemical genetic testing of other sulfatases or molecular genetic testing of the SUMF1 gene to exclude MSD.

 

Normal results (≥1.5 nmol/hour/mL) are not consistent with iduronate-2-sulfatase deficiency.

Clinical Reference

1. D’Avanzo F, Rigon L, Zanetti A, Tomanin R: Mucopolysaccharidosis type II: One hundred years of research, diagnosis, and treatment. Int J Mol Sci. 2020 Feb;21(4):1258. doi: 10.3390/ijms21041258 2. Hopwood JJ, Ballabio A. Multiple sulfatase deficiency and the nature of the sulfatase family. In: Valle D, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019. Accessed February 11, 2021. https://ommbid.mhmedical.com/content.aspx?bookid=2709&sectionid=225546905

3. Neufeld EF, Muenzer J: The Mucopolysaccharidoses. In: Valle D, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019. Accessed April 9, 2021. Available at https://ommbid.mhmedical.com/content.aspx?bookId=2709&sectionId=225544161

4. Scarpa M: Mucopolysaccharidosis Type II. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 2007. Updated October 4, 2018. Accessed February 11, 2021. Available at www.ncbi.nlm.nih.gov/books/NBK1274/

Day(s) Performed

Varies

Report Available

8 to 15 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

82657

LOINC Code Information

Test ID Test Order Name Order LOINC Value
I2SW Iduronate-2-sulfatase, B 79462-8

 

Result ID Test Result Name Result LOINC Value
61902 Iduronate-2-sulfatase, B 79462-8
35211 Reviewed By 18771-6
35212 Interpretation (I2SW) 59462-2

Method Name

Fluorometric Enzyme Assay

Forms

1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Biochemical Genetics Patient Information (T602) in Special Instructions.

3. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.

Testing Algorithm

The following algorithms are available in Special Instructions:

-Lysosomal Storage Disorders Diagnostic Algorithm, Part 1

-Lysosomal Storage Disorders Diagnostic Algorithm, Part 2

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

mml-biochemical