Pompe disease (also known as acid maltase deficiency or glycogen storage disease type II) is caused by a mutation in the GAA gene, which encodes for the enzyme acid alpha-glucosidase or acid maltase. This enzyme is necessary for breaking down glycogen, a complex sugar, in the body.
The mutation causes the enzyme not to work as it should, so patients accumulate glycogen, especially in the smooth muscles, skeletal muscles, and heart muscles. As such, muscle weakness is the predominant symptom of Pompe disease.
Types of Pompe disease
Symptoms of Pompe disease can manifest shortly after birth, in which case the condition is called classic infantile Pompe disease. They can also appear by the first year of life (non-classic form of Pompe disease) or can begin later in life, anywhere from childhood to adulthood, in which case the disease is called late-onset Pompe.
Generally, symptoms tend to be more severe and the disease tends to run a more aggressive course the earlier the symptoms first start to appear.
Symptoms of classic infantile Pompe disease
Infants with this form of Pompe disease experience rapidly progressing muscle weakness and poor muscle tone (floppy infant syndrome). These infants may never be able to sit up, crawl, or stand. They may have difficulty breathing, as the muscles required for respiration are weak. Heart muscles also are abnormally thick and bulky, leading to a condition called hypertrophic cardiomyopathy, which can result in heart failure.
Babies with this type of Pompe disease often have difficulties with feeding, and may not be able to grow and gain weight at normal rates (a condition known as failure to thrive). They may also have an unusually large, protruding tongue (macroglossia), hearing problems, and may rest their legs in a “frog position,” a characteristic sign of this disease.
If untreated, babies with classic infantile Pompe disease often succumb to heart failure within the first year of life.
Symptoms of non-classic infantile Pompe disease
This type of Pompe disease is marked by babies not achieving developmental milestones such as rolling over or sitting. Although these babies may have a larger than normal heart, they do not typically develop heart failure. But muscle weakness is also a predominant feature in this form of Pompe disease, and serious breathing problems may develop.
Children with non-classic infantile Pompe often survive until early childhood.
Symptoms of late-onset Pompe disease
Children and adults with late-onset Pompe experience muscle weakness, primarily affecting muscles such as the shoulder muscles, and the muscles of the upper arms and legs, with the legs being affected more than the arms.
The weakening of the face and throat muscles can cause droopy eyelids and problems with eating and swallowing, leading to a gradual weight loss.
Weak muscles surrounding the spine can also cause abnormal curvature of the spine (scoliosis).
Varying degrees of breathing problems and frequent chest infections may occur due to the weakness of the muscles involved in breathing.
Given the progressive nature of the muscle weakness, it is not uncommon for patients to require a wheelchair or ventilator (a machine that supports breathing).
Patients with late-onset Pompe usually do not have heart problems as serious as those who have infantile Pompe, but they may develop heart conduction problems that lead to abnormal heart rhythms (arrhythmias).
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