Enzyme replacement therapy (ERT) is the only effective treatment for Pompe disease. In this therapy, acid alpha-glucosidase, the enzyme that is deficient in Pompe disease, is given via an injection. This allows patients to break down the glycogen stored up in their tissues into the more usable glucose.
How ERT works
ERT is used to treat genetic diseases in which an insufficient amount of enzyme is produced or the enzyme that is produced is not working properly. For the treatment, the functional enzyme usually is produced in the laboratory by cells that have been genetically modified. The cells are then harvested and the enzyme is purified before being given to the patient.
ERT for Pompe disease
In Pompe disease the enzyme that is given, acid alpha-glucosidase, breaks down glycogen into glucose, reducing its buildup inside cells and giving cells the energy they need. This reduces the muscle wasting and heart problems that the disease can cause.
ERT should be started as early as possible in infants with Pompe disease, and as soon as symptoms appear in adults. Once started, patients need to be on the therapy for their entire lives in order to prevent the glycogen from building up again. The treatment usually is not stopped or interrupted even if negative side effects occur.
Lumizyme is an ERT for Pompe disease produced by Sanofi Genzyme, which is the only ERT currently available in the U.S. The company also produces a similar ERT, marketed under the brand name Myozyme, in Europe.
ERT leads to greater survival rates and improved strength and energy levels. However, due to the difficulties in getting the enzyme across the blood-brain barrier, ERT is not able to correct the neurological symptoms of Pompe disease.
Current research into ERT for Pompe disease
- The use of exercise and low-carbohydrate high-protein diets along with ERT to improve metabolism. Aerobic exercises in combination with ERT can help fight muscle wasting by boosting cellular metabolism. High-protein diets allow muscle cells to repair themselves after exercise and grow stronger. Protein also can be used as an alternate source of energy by the cells.
- The use of medicines that reduce the activity of the immune system, such as methotrexate and rituximab. A clinical trial (NCT01451879), results of which were published in the Journal of Pediatrics, also looked at the effects of sirolimus and mycophenolate in patients who were actively using or were about to begin using ERT. These medications appeared to reduce or eliminate adverse side effects associated with ERT.
- The use of pharmacologic chaperones, molecules that help enzymes keep their shape. Research has shown that, when used alongside ERT, chaperones ensure the injected enzyme does not get broken down too early. They also encourage the production of functional enzymes by the body by helping the enzymes fold properly; this reduces the dose of enzyme the patient will need, which reduces the risk of side effects.
Side effects of ERT
ERT has several side effects. Many of these are due to the body reacting to the needle and fluids involved in the intravenous delivery of the enzyme. The influx of fluid can cause electrolyte problems, and the body may respond with swelling and irritation around the injection site or a more general fever.
Other side effects involve an allergic immune reaction to the enzyme itself. Their immune system marks the enzyme as a foreign substance and attacks it, which can lead to problems as severe as anaphylaxis, a life-threatening allergic reaction that requires immediate treatment.
Other side effects may include:
- Allergy symptoms, including hives, a rash, fever, or life-threatening anaphylaxis
- Flushed skin, feelings of excessive heat or cold, and chills
- Low oxygen in the blood, resulting in pale, bluish, or purple skin
- Quickened heart rate and rapid breathing
- Headache, dizziness, or fainting
- Chest discomfort
- High or low blood pressure
- Muscle tremors, pain, or fatigue
- Nausea and vomiting
In Pompe disease, higher doses of alpha-glucosidase enzyme may be needed compared to other diseases, increasing the risks of these side effects.
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