Pompe disease is a progressive and rare condition that mainly affects muscles. It’s caused by a deficiency in the acid alpha-glucosidase enzyme, which is responsible for the breakdown of a complex sugar molecule called glycogen inside cells.

The genetics of Pompe disease

Mutations in the GAA gene, which contains instructions for making the acid alpha-glucosidase enzyme, are responsible for causing the disease.

So far, 500 different mutations have been identified in the GAA gene in families with Pompe disease. These mutations can cause no functional alpha-glucosidase enzyme to be produced or only partially functional enzyme to be made. This in turn causes glycogen to accumulate inside cells to toxic levels eventually killing them.

The onset and course of Pompe disease depends on the severity of functional defects the GAA mutations cause in the acid alpha-glucosidase enzyme.

Late-onset Pompe disease patients may have up to 40 percent of normal levels of functional enzyme, which may be sufficient for them to lead a symptom-free life for decades. On the other hand, patients with classic-onset Pompe disease may have as little as 1 percent functional enzyme and are severely affected by the disease, often not surviving past their first birthday.

How is Pompe disease inherited?

Patients inherit Pompe disease from their parents. Everybody receives two copies of each gene, one from each parent. Pompe is a genetic disease that is inherited in an autosomal recessive pattern, meaning that a person develops the disease only if both copies of the GAA gene they inherit are faulty.

People with one mutated copy of the gene are called carriers. They do not show any symptoms, but they can pass the mutated gene on to their children. When both parents are carriers, each of their children has a 25 percent risk of developing Pompe disease.

If one of the parents has Pompe and the other does not, all of the children will be carriers and will have a risk of passing the disease on to their own children.

Who gets Pompe disease?

Women and men have the same risk of inheriting disease-causing mutations, because the GAA gene is located in one of the autosomal chromosomes, and not in the sex chromosomes.

On average, one in 40,000 newborns have Pompe disease. But the incidence varies among geographical regions and ethnic groups. African-Americans and people from southern China and Taiwan appear to be more likely to have Pompe disease, with Pompe affecting up to one in 14,000 people in these regions and ethnicities.

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