Infantile-onset Pompe Disease
What causes someone to have infantile-onset Pompe disease?
Pompe disease is a disorder caused by the deficiency of an enzyme, acid alpha-glucosidase (GAA). GAA is responsible for breaking down glycogen 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 accumulation of glycogen causes the symptoms seen in babies with infantile-onset Pompe disease.
Infantile-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: infantile-onset and late-onset. In the late-onset form, people may show their first symptoms in childhood or early adulthood. The first signs are often muscle weakness in the abdomen and upper legs. A person's ability to breathe is affected, as the muscles used to breathe become weaker.
Sometimes people divide late-onset Pompe disease into "juvenile-onset" and "adult-onset," based on the severity of the childhood symptoms.
How common is infantile-onset Pompe disease?
A research study published in 1999 reported that about 1 in every 140,000 babies will have infantile onset Pompe disease. The late-onset form of Pompe disease is more common, with 1 in every 60,000 people affected. It is believed that there are 5,000-10,000 people living with Pompe disease worldwide.
What are the signs and symptoms of infantile-onset Pompe disease?
Newborn babies with Pompe disease often do not show signs of the condition. As a baby gets older, parents may notice that he / she dos not feed well, does not like to lie on his / her stomach, or does not learn to lift his / her head. Parents may also notice that their baby's tongue often sticks out of his / her mouth.
A child's pediatrician may notice that he / she has very low muscle tone and absent reflexes. A doctor may also find that the baby's liver is enlarged. A chest X-ray, echocardiogram, or electrocardiogram may show that the baby has an enlarged heart.
The muscle weakness worsens as the infant gets older. The muscle weakness affects the baby's ability to feed, which can cause the baby not to gain weight or to gain weight slowly. The muscles used to breathe also weaken, which means that the baby may not get enough oxygen. As the muscles weaken, the baby can lose the ability to do things he / she could do before, such as lift toys and kick.
Colds and respiratory infections can make a baby with Pompe disease very sick. If a baby cannot breathe very well when it is healthy, a cold can be very dangerous.
A baby with Pompe disease may need feeding tubes to help him / her feed and gain weight. He / she may also need extra oxygen, or even a ventilator, to help him / her get enough oxygen.
Infantile-onset Pompe disease often causes a child to die before he / she is one-year old. A baby can die from an abnormal heart rhythm caused by the enlargement of the heart or complications of breathing problems, as well as other causes.
How is infantile-onset Pompe disease diagnosed?
A doctor may suspect infantile Pompe disease for a number of reasons. A doctor may suspect Pompe disease in a baby who has severe hypotonia, feeding problems, or respiratory insufficiency. An echocardiogram, chest X-ray, or electrocardiogram may show a large heart. A muscle biopsy may detect increased glycogen in the muscle cells.
One specific test must be done to make a definite diagnosis of Pompe disease. This test measures the enzyme, acid alpha-glucosidase (GAA). If the test shows very low or no GAA activity, this proves the child 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 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 very difficult for parents and family members.
What kinds of treatment are available for infantile-onset Pompe disease?
There is no cure for Pompe disease at this time. Doctors treat the symptoms of the disease and try to make the child as comfortable and healthy as possible. Oxygen can be given by a tube under the nose, or a ventilator may be used, when a child is too weak to get enough oxygen by breathing air. A feeding tube can help a baby get calories and nutrition if he / she gets too tired from feeding from a bottle or breast. Physical therapy can help maintain muscle strength and keep the joints healthy. Medicines may be used to help the baby's enlarged heart function.
Genetics professionals, pediatricians, cardiologists, physical therapists, pulmonologists and respiratory therapists are some of the medical professionals that may be a part of the medical team caring for an infant with Pompe disease.
Is anyone doing research on infantile-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. Data from these trials is not yet publicly available.
The National Institutes of Health (NIH) maintains a web site that lists all clinical trials 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?
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 National Organization for Rare Disorders (NORD) is a federation of organizations dedicated to helping people with rare diseases. 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 Association for Glycogen Storage Disease offers support to families, produces educational materials for families and promotes awareness and research. http://www.agsdus.org
The Muscular Dystrophy Association promotes research and awareness of neuromuscular diseases. http://www.mdausa.org/
Written 2/05
