Late-onset Pompe Disease
What causes someone to have late-onset Pompe disease?
Pompe disease is a disorder caused by having too little of an enzyme, acid alpha-glucosidase (GAA). GAA is responsible for breaking down glycogen (a carbohydrate) in a compartment of the cell called a lysosome. Once the glycogen is broken down, it can be used by the body. In Pompe disease, an affected individual has no or very little GAA, causing glycogen to build up in the lysosome. With time, more and more glycogen builds up in the lysosomes in various body tissues. The progressive build-up of glycogen causes the symptoms seen in individuals with late-onset Pompe disease.
Late-onset Pompe disease is also known as glycogen storage disease type II (GSD-II) or acid maltase deficiency (AMD).
Are there different types of Pompe disease? How do the types differ?
Most sources say there are two types of Pompe disease: the infantile-onset form and the late-onset form. In the infantile-onset form, babies show their first symptoms during the first months of life. Babies with the infantile-onset form of Pompe disease have enlarged hearts and profound muscle weakness, which affects their ability to feed, breathe and learn motor skills.
Sometimes late-onset Pompe disease is divided into "juvenile-onset" and "adult-onset," based on the severity of the childhood symptoms.
How common is late-onset Pompe disease?
A 1999 study reported that about 1 in every 140,000 newborns will have infantile onset Pompe disease. The late-onset form of Pompe disease is more common, with 1 in every 60,000 people affected. There may be as many as 5,000 to 10,000 people living with Pompe disease worldwide.
What are the signs and symptoms of late-onset Pompe disease?
A person with late-onset Pompe disease does not show symptoms of the condition at birth. As children, individuals with late-onset Pompe disease may seem clumsy and may have difficulty keeping up with their classmates in gym class because they may tire easily or be unable to perform certain activities, such as sit-ups. Individuals may also have difficulty gaining and maintaining body weight.
The disease is often not diagnosed, however, until individuals have more severe symptoms. Symptoms are progressive and may become more noticeable in childhood, adolescence, or early adulthood. Trunk muscle weakness, including the muscles that support breathing, can weaken, causing difficulty breathing, scoliosis and back pain. Individuals may need to sit up very straight in order to breathe well. Leg muscle weakness is also progressive and may be first noticed as a difficulty climbing stairs. These symptoms can look like a muscular dystrophy, and affected individuals may be tested for muscular dystrophies before Pompe disease is considered as a diagnosis.
Respiratory insufficiency may lead to sleep apnea, daytime headaches and morning drowsiness. Daytime and / or nighttime breathing assistance may be needed to help individuals get enough oxygen and clear carbon dioxide from their bodies. Persons with Pompe disease can be susceptible to respiratory infections.
How is late-onset Pompe disease diagnosed?
One specific test must be done to prove a diagnosis of Pompe disease. The test measures the enzyme, acid alpha-glucosidase (GAA). If the test shows very low or no GAA activity, this proves the individual has Pompe disease.
To do this test, a doctor must take a skin biopsy, which is a small piece of skin that is usually removed from the leg, arm or shoulder. The skin is numbed, and a special tool is used to remove a small piece of skin. This procedure is performed in a clinic and takes about 10 minutes. The place where the skin is removed bleeds a little bit, but a Band-Aid can control the bleeding. No stitches are needed.
The skin sample is then taken to a laboratory, where the skin cells are grown. In about 2 weeks, there are enough skin cells to do the enzyme test. The enzyme test takes about 1 week to perform, which means test results are available about 3 to 4 weeks after the skin biopsy is performed. This is a long time to wait for test results, and the wait is difficult for individuals and their family members.
What kinds of treatment are available for late-onset Pompe disease?
There is no cure for Pompe disease at this time.
Occupational therapy may help individuals adapt their daily home and employment tasks to their physical abilities.
Respiratory therapy and daytime and / or nighttime breathing assistance may be used to assist individuals with respiratory insufficiency.
Equipment such as a cane, walker or wheelchair may be used to help individuals maintain independence and mobility.
Nutritionists or dietitians may help individuals to build a diet plan that allows adequate calorie intake and weight maintenance.
Individuals with any chronic illness, as well as their partners and families, may be at risk for depression. Psychologists, family counselors or marriage therapists help families cope with the difficulties of living with a chronic illness.
Geneticists, internists, pulmonologists, respiratory therapists, orthopedic specialists and occupational therapists are some of the medical professionals that may be a part of the medical team caring for a child or adult with late-onset Pompe disease.
Is research being done on late-onset Pompe disease?
The STAR Lysosomal Center of Cincinnati is currently participating in two of several clinical trials sponsored by a pharmaceutical company to test the safety and effectiveness of enzyme replacement therapy for treatment of Pompe disease. Initial results from completed studies are encouraging. Data from the on-going trials are not yet publicly available.
The Cincinnati STAR Center for Lysosomal Diseases is also participating in a patient registry for Pompe disease. This registry is being used internationally to collect information on individuals with Pompe disease. The information collected will be used to help physicians develop a better understanding of the condition and how it affects people. If you are interested in participating in the Pompe disease Registry, you can contact the Cincinnati STAR Center for Lysosomal Diseases at 1-800-647-4805.
The National Institutes of Health (NIH) maintains a web site that lists all clinical trials that are recruiting participants in the United States. To search for clinical trials, visit www.clinicaltrials.gov
Where can I go to get more information on infantile-onset Pompe disease?
Cincinnati STAR Center for Lysosomal Diseases
Telephone: 1-800-647-4805
Fax: 513-636-0124
Mail:
Cincinnati STAR Center for Lysosomal Diseases
C / o Debbie Baker
Cincinnati Children's Hospital Medical Center
Division of Human Genetics
3333 Burnet Avenue ML 4006
Cincinnati, OH 45229
The National Organization for Rare Disorders (NORD) is a unique federation of voluntary health organizations dedicated to helping people with rare diseases and assisting the organizations that serve them. NORD is committed to the identification, treatment and cure of rare disorders through programs of education, advocacy, research and service.
http://www.rarediseases.org/
The Acid Maltase Deficiency Association (AMDA) was formed to fund research and to promote public awareness of Acid Maltase Deficiency, also known as Pompe Disease.
http://www.amda-pompe.org/
The Muscular Dystrophy Association is a not-for-profit agency that promotes research and awareness of neuromuscular diseases. http://www.mdausa.org/
Written 2/05
