What is Pompe?
Pompe is a glycogen storage disorder caused by the buildup of glycogen in the body’s cells. This happens because people with this disorder lack an enzyme known as alpha glucosidase. Alpha glucosidase is primarily responsible for breaking down glycogen in the body. Since there is a lack of this enzyme, glycogen buildup occurs in the body’s cells, tissues, muscles and organs.
Pompe is also known as:
- Acid maltase deficiency (AMD)
- GAA deficiency
- Glycogen storage disease type II
Across the globe, Pompe affects 1 in every 40,000 persons. Pompe occurs equally among males and females.
Types of Pompe
There are three major types of Pompe based on the severity and age of onset:
- Classic form - of Pompe is seen within a few months of birth. Infants begin to experience poor muscle tone (hypotonia), enlarged liver (hepatomegaly), cardiac defects and muscle weakness (myopathy). Babies usually present with respiratory issues and this can even lead to pneumonia and fatality if untreated.
- Non-classic form - of Pompe usually presents around the age of 1. Babies usually have difficulties with motor skills. They may not be able to sit up on their own, crawl or walk. Muscle weakness is progressive coupled with degenerating heart and respiratory issues. Untreated children with Pompe may not make it beyond the age of 5.
- Late onset - is the mildest form of Pompe. It may not appear until late childhood, adolescence or even adulthood. Most people with this type of Pompe experience weakness in the lower limbs. Progressive muscle weakness can ultimately lead to cardiac and respiratory issues.
Patterns of Inheritance
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Pompe is an autosomal recessive disorder which means both parents have the carrier gene with 25% chance of each child having the disease. Pompe is caused by various mutations in the acid alpha-glucosidase (GAA) gene. A child with Pompe inherits two copies of the mutated GAA gene from each parent and hence expresses the disease.
Signs and Symptoms
Signs and symptoms of Pompe vary depending on the type. These include:
- Progressive muscle weakness (floppy babies)
- Low muscle tone (hypotonia)
- Breathing issues
- Cardiomyopathy (abnormal thickening of the walls of the heart)
- Failure to achieve milestones like turning over, crawling, sitting up, walking
- Legs rest in frog position
- Infants present with a large protruding tongue
- Liver enlargement
- Feeding and swallowing difficulties
- Non-classic Pompe patients may experience weakness in lower limbs
- Scoliosis or curvature of the spine is common in adolescent Pompe
If the pediatrician suspects Pompe, he/she will usually take a family history and history of the child’s symptoms along with a detailed clinical examination of the child. Some of the tests that are used to diagnose MD include:
- biochemical tests - to measure the activity level of the enzyme GAA. Individuals with Gaucher will have low levels of this enzyme activity. Other tests like Creatinine Phosphokinase (CPK) may also be done. An electrocardiogram may be done to see if the heart is enlarged.
- molecular test - DNA tests like Next Generation Sequencing (NGS) to locate the exact mutation causing the form of Pompe. This test is basically a DNA analysis of the GAA gene.
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Treatment and Management
Currently, no permanent cure is available for Pompe. Treatment is aimed at preventing complications and enabling independent living. An interdisciplinary team of doctors including pediatricians, neurologists, orthopedicians, pulmonologist, cardiologist and physiotherapists will be required to take care of the clinical needs of the child/adult. In the early stages when just diagnosed, it is important to immediately start ERT treatment to prevent further deterioration and prevent organ damage.
ERT involves balancing low levels of GAA with external enzymes like recombinant human acid α-glucosidase. This is an intravenous (IV) infusion every 2 weeks which can even be taken at home. ERT helps in reducing symptoms like hepatosplenomegaly, bone weakness and low platelet counts. Currently, the enzyme is manufactured and marketed by Sanofi Genzyme under the name Myozyme in India. The company has a charity access program under which many children’s lives have been saved by supplying free ERT.
Supportive treatment may include respiratory support like bipap or ventilators if needed. Physiotherapy is highly recommended to preserve muscle strength. Wheelchairs may be required in some cases. Orthopedic surgeries for scoliosis may become necessary at some point in time. Some children also required feeding and nutritional support with the aid of a feeding tube and special high-calorie supplements.
Investigational therapies like gene therapy and gene editing are in the clinical research stage and proving to be exciting. Gene therapy involves transducing a functional GAA gene in the liver cells in vivo or ex vivo through bone marrow transplants. It may not be far when patients with Pompe may be able to access such permanent curatives.
Living with Pompe
Children and adults with Pompe must be encouraged to participate in all life activities and must be encouraged to go to regular schools, colleges and participate in social activities. Genetic counselling and psychosocial counselling must be made available whenever required with other supportive measures.Look up our list of patient organizations in India for help and support
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Prenatal Testing and Pompe
If there is a known case of Pompe in the family, it is absolutely essential for closest female relatives like siblings, uncles, aunts and cousins to test for carrier status.
If a woman with a carrier status is pregnant, prenatal test is essential to determine if the fetus has the disease mutation.
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