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Test ID: MPS2Z    
Hunter Syndrome, Full Gene Analysis, Varies

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Useful For Suggests clinical disorders or settings where the test may be helpful

Confirmation of a diagnosis of mucopolysaccharidosis type II (Hunter syndrome)

 

Carrier testing when there is a family history of mucopolysaccharidosis type II (Hunter syndrome), but disease-causing variants have not been previously identified

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

Testing includes full gene sequencing of the IDS gene.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

If a skin biopsy is received, fibroblast culture and cryopreservation for biochemical studies will be performed at an additional charge.

 

See Lysosomal Storage Disorders Diagnostic Algorithm, Part 1 in Special Instructions.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Mucopolysaccharidosis type II (MPS-II), also known as Hunter syndrome, is a rare X-linked condition caused by variants in the IDS gene. MPS-II is characterized by reduced or absent activity of the iduronate 2-sulfatase enzyme.

 

The clinical features and severity of symptoms of MPS-II are widely variable, ranging from severe disease to an attenuated form, which generally presents at a later onset with a milder clinical presentation. In general, symptoms may include coarse facies, short stature, enlarged liver and spleen, joint contractures, cardiac disease, and profound neurologic involvement leading to developmental delays and regression. Female carriers are usually asymptomatic.

 

The IDS gene is located on the X chromosome and has 9 exons and is the only known gene to be associated with MPS-II. The recommended first-tier test for mucopolysaccharidosis type II is biochemical testing that measures iduronate 2-sulfatase enzyme activity in blood: I2SW / Iduronate-2-Sulfatase, Whole Blood or blood spots: I2SBS / Iduronate-2-Sulfatase, Blood Spot.

 

Individuals with decreased or absent enzyme activity are more likely to have a variant in the IDS gene identifiable by molecular genetic testing. However, enzymatic testing is not reliable to detect carriers. Additionally, measurement of mucopolysaccharides in blood can aid in diagnosis and ongoing therapeutic monitoring (MPSBS / Mucopolysaccharidosis, Blood Spot).

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation Provides information to assist in interpretation of the test results

All detected alterations are evaluated according to American College of Medical Genetics and Genomics (ACMG) recommendations.(1) Variants are classified based on known, predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or known significance.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

A small percentage of individuals who are carriers or have a diagnosis of mucopolysaccharidosis type II (MPS-II) may have a variant that is not identified by this method (eg, large genomic deletions, promoter alterations). The absence of a variant, therefore, does not eliminate the possibility of positive carrier status or the diagnosis of MPS-II. The preferred approach to carrier testing is to first document the presence of an IDS gene variant in an affected family member.

 

In some cases, DNA alterations of undetermined significance may be identified.

 

Rare alterations exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.

 

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in the interpretation of results may occur if information given is inaccurate or incomplete.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Richards S, Aziz N, Bale S, et al: Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med. 2015 May;17(5):405-424

2. Martin R, Beck M, Eng C, et al: Recognition and diagnosis of mucopolysaccharidosis II (Hunter syndrome). Pediatrics. 2008;121(2):e377-386

3. Wraith JE, Scarpa M, Beck M, et al: Mucopolysaccharidosis type II (Hunter syndrome): a clinical review and recommendations for treatment in the era of enzyme replacement therapy. Eur J Pediatr. 2008;167(3):267-277

Special Instructions Library of PDFs including pertinent information and forms related to the test