How MPS VI is Diagnosed

Because MPS VI is a progressive disease, it is important to diagnose the disease as early as possible. Early diagnosis increases the chance that a person with MPS VI will receive appropriate medical care soon enough to avoid preventable complications, such as loss of hearing caused by repeated ear infections.

The key to early diagnosis is seeing a doctor who specializes in lysosomal storage disorders and MPS disorders. This is usually a geneticist or a metabolic specialist. Once a person has been referred to an appropriate specialist, the diagnosis of MPS VI is confirmed by laboratory tests. The section below describes the types of tests that a doctor may order to diagnose MPS VI. Having this information will help you to communicate effectively with your doctor or your friend or family member's doctor.

Testing for MPS VI - What to Expect

Urine GAG Measurement

A doctor looking for possible MPS VI may order a urine test that measures the amount or type of GAG in the urine. Since GAGs build up in the bodies of people with MPS VI and other MPS disorders, a high GAG level in the urine means that MPS VI or another MPS disorder is likely. Urine tests aren't always specific or accurate—they may only reveal that a person has MPS, without revealing the specific type—so they should be followed up by an enzyme measurement test.¹

Enzyme Measurement

A doctor may also order a test to measure enzyme levels. An enzyme test provides a definite diagnosis of MPS VI, because these tests specifically measure the amount of arylsulfatase B (ASB) in a person's cells (using either skin cells or blood cells). Since people with MPS VI are deficient in the ASB enzyme, a low reading on this test confirms the diagnosis of MPS VI.¹

Prenatal Tests

For parents who are known to be carriers (parents who have already had a child with MPS VI), prenatal diagnosis is available for subsequent pregnancies. In this test, ASB enzyme is measured in fetal cells collected by either chorionic villus sampling (CVS) or amniocentesis.^1,2

Carrier Tests

Unaffected siblings of MPS VI individuals may want to know if they are carriers, particularly when they begin to plan to have their own families. The most accurate method of carrier testing is a genetic test that checks to see if one of their copies of the ASB gene is a nonworking copy (see How MPS VI Is Inherited—A Primer for Parents for a complete explanation). Sometimes gene tests aren't possible. In this case carrier testing can be attempted by measuring the amount of ASB enzyme in their blood cells or skin cells. However, this method is often uninformative due to the overlap in enzyme levels between carriers and noncarriers.¹

Specialized MPS Testing Laboratories

All of the tests described here are highly specialized, and therefore should be carried out in an experienced laboratory under the direction of a physician specialist in medical genetics or metabolic diseases.

1. Neufeld EF, Muenzer J. The mucopolysaccharidoses. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The Metabolic and Molecular Bases of Inherited Disease. Vol 3. 8th ed. New York, NY: McGraw- Hill; 2001:3421-3452.
2. Muenzer J. The mucopolysaccharidoses: a heterogeneous group of disorders with variable pediatric presentations. J Pediatr. 2004;144(5 Suppl):S27-S34. Review.