How is Pompe disease inherited?
Pompe disease is caused by a change (also called a mutation or a variant) in the GAA gene which causes the gene to not work correctly. The GAA gene carries the instructions for making the alpha-glucosidase enzyme, also called acid maltase, which is important for breaking down glycogen in the body. We normally have two working copies of GAA in our cells and we inherit one copy from our biological mother and the other from our biological father. In order to develop symptoms of Pompe disease, both copies of GAA are not working properly. This is also called autosomal recessive inheritance, which means that both parents of someone with Pompe disease are carriers of one working and one non-working copy of the GAA gene. Since each parent has one working copy, they don't have symptoms of Pompe disease themselves. However, when they have children, they each have a 1 in 2 or 50% chance of passing on the non-working copy to their child. When both parents are carriers, there is a 1 in 4 or 25% chance of both of them passing on the non-working copy and having a child with Pompe disease. Even if a couple already has one child with Pompe disease, it is important to know that they can have another affected child because the chances are 1 in 4 for each pregnancy.
Genetic Alliance; "How Do I Talk To My Family About Pompe?"
Pompe Disease - Inheriting Pompe Disease https://www.pompe.com/en/patients/inheriting-pompe.aspx