Diagnosis and Testing

Before a diagnosis is made, patients may see several specialists, since some of the early signs and symptoms of MPS I are commonly seen in many children. Because MPS I is a rare disease, physicians may not consider MPS I as a diagnosis.

To diagnose MPS I, a doctor will typically first do a urine test to look for abnormally high levels of glycosaminoglycans (GAGs). The results are compared to known reference ranges for various ages. Most individuals with MPS I have GAG levels in their urine that are higher than those of individuals without MPS I.

A urine test is only one of the first steps in diagnosing MPS I; definitive diagnosis requires a test to measure enzyme activity levels in the blood or skin cells. In healthy individuals, the tests show white blood cells, serum, and skin cells that contain normal enzyme activity. In individuals with MPS I, the enzyme activity is much lower or absent.

DNA testing can detect the specific genetic changes that code for the missing enzyme. DNA testing is substantially more costly than enzymatic testing, due to limited availability and the use of specialized lab techniques. For example, while we know that every individual with MPS I has a deficiency of alpha-L-iduronidase, the underlying DNA changes that cause that deficiency can differ among families.

Early diagnosis is critical. The earlier that MPS I is diagnosed, the sooner potential treatment options can be explored and supportive care may be initiated to prevent some of the irreversible damage caused by the disease.

Family Screening

Because MPS I is an inherited disorder, family screening is extremely important. One diagnosis of MPS I may uncover other affected siblings within a family. With early diagnosis, the disease may be better managed.

A genetic counselor can be a valuable resource to help you understand how MPS I is inherited in families. A genetic counselor may also provide guidance to families for diagnostic, medical, and support services. For more information about genetic counseling, visit the National Society of Genetic Counselors website.

Prenatal Testing

Prenatal testing allows pregnant women to find out if the baby they are carrying is affected by MPS I. There are two tests that can be used: chorionic villus sampling (taking a sample of the membrane around the developing baby) and amniocentesis (taking a sample of the amniotic fluid). A doctor may advise on specific prenatal testing options. Talking with a genetic counselor or doctor can help explore these options and their implications.

Newborn Screening

Newborn screening is the testing of newborn babies to see whether they have a genetic disorder. The goal is to help with early diagnosis and treatment. Each state makes its own decisions about which health conditions should be included in their newborn screening programs.