Whether or not a person has Pompe disease comes down to the genes that they have received from their parents.
In people with Pompe disease, the gene responsible for telling cells to make GAA is faulty, so not enough GAA is produced, or in some cases virtually no GAA is produced. As explained earlier, this results in a build‐up of a substance called glycogen in muscles, which causes the health problems that can occur with Pompe disease (see ‘What causes Pompe disease?’ section]. There’s nothing that a person with Pompe disease could have done to stop themselves from having the condition; it’s caused by the faulty ‘GAA genes’ they inherited from their parents. This is not something that parents have any control over.
How is Pompe disease passed on in families?
- If both ‘GAA genes’ in the pair are normal, the person will not have Pompe disease
- If both ‘GAA genes’ in the pair are faulty, the person will have Pompe disease
- If one ‘GAA gene’ is normal and the other is faulty, the person will be a ‘carrier’ of Pompe disease
Carriers do not have Pompe disease themselves, but they do have a faulty ‘GAA gene’ and may pass this on to their children. Although Pompe disease carriers have one faulty ‘GAA gene’, their other normal ‘GAA gene’ enables production of GAA, so harmful build-up of glycogen doesn’t happen. Even though the amount of GAA that they make is usually lower than normal, carriers have no symptoms of Pompe disease.
The odds of passing Pompe disease to children
- There is a 1 in 4 (i.e. 25%) chance that the child will inherit 2 faulty ‘GAA genes’ and thus have Pompe disease
- There is a 2 in 4 (i.e. 50%) chance that the child will inherit 1 faulty ‘GAA gene’ and thus be a carrier of Pompe disease (but not have Pompe disease themselves)
- There is a 1 in 4 (i.e. 25%) chance that the child will inherit 2 normal ‘GAA genes’ and thus be completed unaffected (won’t be a sufferer or carrier of Pompe disease)
The above situation, in which both parents are carriers of Pompe disease, is the most common scenario. But what if both parents actually have Pompe disease?
In this instance, every child that they have together is certain to have Pompe disease too. If one parent has Pompe disease and the other is a carrier, each child that they have together has a 1 in 2 (i.e. 50%) chance of having Pompe disease and a 100% chance of being a carrier. In other words, even if the child does not have Pompe disease, they are certain to be a carrier of it.
Inheritance possibilities when ‘Pompe carriers’ have a child together