• Overview
• Inheritance
• Symptoms
  • Growth, Bones and Joints
  • Brain and Nerves
  • Physical Appearance
  • Ear, Nose, Throat and Chest
  • Heart
  • Liver, Spleen and Abdomen
  • Eyes
• Testing
• Treatment
• Resources
• Aldurazyme Update

Enzyme Testing

Diagnosis
The most accurate diagnosis of Hurler syndrome is made based on the results of a blood test that measures the level of alpha-L-iduronidase enzyme activity. In people with Hurler syndrome, the amount of enzyme activity is much lower than normal. This testing can also be used to diagnose Hurler-Scheie and Scheie syndromes. The results of enzyme testing often cannot reliably predict which form of MPS type I a person has and/or how severe their disease will be.

Carrier testing
Enzyme testing is not as reliable for detecting Hurler carriers, since some carriers have an alpha-L-iduronidase level in the normal range. However, this testing can provide definite information on carrier status for some people.

DNA testing
DNA testing, also done on the blood, can detect alpha-L-iduronidase gene mutations that cause Hurler syndrome (or Hurler-Scheie syndrome or Scheie syndrome). DNA testing is not generally done to diagnose Hurler syndrome; however, it may be useful to confirm a diagnosis made by enzyme testing. DNA test results do not necessarily relate to a person's form of MPS type I, the severity of their disease, or their specific symptoms, and the test result will not change medical treatment.

Identifying which Hurler gene mutations are present in an affected person may also be helpful to other family members who wish to know if they are a carrier of one of those mutations. Carrier testing by DNA analysis may be available to relatives of people with Hurler syndrome and to partners of Hurler carriers. Carrier testing by enzyme analysis may also be helpful in this situation.

Prenatal diagnosis of Hurler syndrome may be available in pregnancies involving a fetus known to be at risk.

DNA testing for Hurler syndrome is performed only in some specialized genetics laboratories. Generally, people who have DNA testing first meet with a genetic counselor, who can explain the testing in more detail and answer any questions. The genetic counselor can also help explain the test results, once they are available. Cindy Morgan, MS is a genetic counselor at the Center; she is available to meet with patients to discuss DNA testing and other genetic issues.