How is Pompe's disease inherited?

 

Pompe disease is inherited through our genes. Genes provide the instructions for all processes in our body and therefore also for the production of the enzyme GAA. Someone with Pompe disease has a defect in his or her gene, resulting in insufficient or even no GAA production. In addition, some patients may have sufficient amounts of the enzyme, but the enzyme does not work as it should. [1]

Everyone has two copies of each of the genes that contain human DNA. One is inherited from the mother and one from the father. Now that you know that, it's easier to imagine how people with Pompe disease are born.

 

Pompe disease is transmitted from parent to child and is considered to be an autosomal recessive condition. Autosomal refers to the fact that the gene for GAA is on one of the 22 chromosome pairs called autosomes. Recessive means that in order to get the disease a person must inherit two copies of the abnormal gene, one from each parent. People who have only one copy of the abnormal gene are called carriers and usually do not show the symptoms of the disease. [1]

 

 

But it is not because both parents are carriers that every child will automatically have the disease. That is because a carrier parent has one normal gene and one abnormal gene. As a result of this genetic 'lottery' there are four possible results when two parents who have an abnormal gene father a child.

 

Four possible results when both parents are carriers

 

Four possible results when both parents are carriers

  • The child receives two abnormal copies of the gene, one from each parent.
  • The child receives one abnormal gene from the father, one normal gene from the mother.
  • The child receives one abnormal gene from the mother, one normal gene from the father.
  •  The child receives two normal copies of the gene, one from each parent.

Note: the hereditariness of Pompe disease is not sex-linked; men and women are equally affected.

When both parents are carriers, there is a 25% chance (1 in 4) of each pregnancy that the child will have two abnormal gene copies and will therefore be born with Pompe disease. But there is an equal chance that the child will get two normal genes and will not get the disease. If the child receives only one abnormal copy of the gene, it will become the carrier of the disease. There is a 50% chance (2 out of 4) that this happens. Carriers generally remain healthy since the one normal gene produces enough GAA to degrade lysosomal glycogen.

 

References

  1. 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, eds. The Metabolic and Molecular Bases of Inherited Disease. 8th Edition. New York: McGraw-Hill, 2001. 3389-3420.