Family Testing

Although Pompe disease is very rare, it can run in families because it is inherited, meaning that it gets passed on to people through their parents. If someone is diagnosed with the disease, there is a risk that relatives may also have the disease or be carriers. It is particularly important to test siblings of an affected child.

Find out more about how Pompe disease is inherited 

The symptoms of Pompe disease can emerge very slowly and at any age, so it is possible for someone to have it even if they are not experiencing any apparent problems. Because early diagnosis is so important in managing the disease, families with a history of it may want to consider several testing options.

Identifying Affected Family Members

The standard test for conclusively diagnosing Pompe disease is an enzyme assay, which measures the person’s levels of the GAA enzyme activity. People affected by the disease have lower than normal enzyme activity, usually in the range of 1-40% of normal levels[1], [2] (and sometimes none at all).

Learn more about enzyme assays to confirm a diagnosis 

Analyzing Genes

If a person’s enzyme levels are at the higher end of the range, it may sometimes be difficult to conclude whether they are affected by the disease—especially if they have no apparent symptoms. In this case, mutation analysis (also called genotyping) can be useful.[1] It involves analyzing a DNA sample from a person to see if their GAA gene has the mutation, or defect, that causes Pompe disease.

Carriers & Inheritance Risks

Like all genes in the body, the GAA gene comes in a pair of two copies—one inherited from each parent. If both genes in the pair have a mutation, the person has Pompe disease. If only one gene has the mutation, the person is considered a carrier.

Mutation analysis is the only way to identify carriers, who do not have the disease, but “carry” the gene defect and may pass it on to their own children—so it’s particularly important to identify carriers within families with a history of the disease.

Figure 1. Autosomal Recessive Inheritance 

 

Pompe disease is inherited in an autosomal recessive manner. Thus, both parents of a child with the disease must be carriers of a mutant gene for GAA, and each child born to them has a 25% chance of having the disease, a 50% chance of being a carrier, and a 25% chance of neither having the disease nor being a carrier.

Testing Children & Babies

Parents who have Pompe disease, or who are carriers, or who have a family history of the disease are likely to have concerns about their own children.

  • Enzyme assays and mutation analysis can be performed on children of any age, including newborn infants, since they require only a very tiny blood sample.
  • Prenatal testing is also available using a tissue sample taken from the amniotic fluid. The test can be performed as early as the 12th week of pregnancy and can provide results as quickly as a few days.[1], [3]

Take Note: Genetic Counseling

A diagnosis of Pompe disease can be overwhelming and raise many questions. Genetic counselors are health care professionals specially trained to educate families on the disease’s inheritance patterns and risks, as well as support them through testing and family-planning decisions.

Find out more about how genetic counseling can help families 

References

  1. Kishnani PS, Steiner RD, Bali D et al. Pompe disease diagnosis and management guideline. Genet Med 2006 8:267-88.
  2. Hirschhorn, Rochelle and Arnold J. J. Reuser. Glycogen Storage Disease Type II: Acid Alpha-glucosidase (Acid Maltase) Deficiency. In: Scriver C, Beaudet A, Sly W, Valle D, editors. The Metabolic and Molecular Bases of Inherited Disease. 8th Edition. New York: McGraw-Hill, 2001. 3389-3420.
  3. Lake BD, Young EP, Winchester BG. Prenatal diagnosis of lysosomal storage diseases. Brain Pathol 1998 8:133-49.

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