What is Pompe disease?
Pompe disease is a rare, inherited neuromuscular disorder. It’s caused by a shortage of the enzyme that processes glycogen in the body. Without this enzyme, glycogen builds up in muscle, tissue, and organs, and weakens them.
Glycogen is a complex sugar that breaks down into glucose. Glucose is a simple sugar that provides energy for your body’s cells.
The severity of the disease depends on your age at onset. Infants born with the disease didn’t use to survive past age 2, but some now are with treatment. Later-onset Pompe disease is milder, but progressively disabling. There’s no cure, but enzyme replacement therapy (ERT) is a promising therapy that may extend lifespan.
Did you know?
Pompe disease is also called acid maltase deficiency or glycogen storage disease type II. It was first described in 1932, by A.J. Pompe, a Dutch doctor.
What are the types of Pompe disease?
Pompe disease has been categorized into three types, depending on the age at which it first appears and its severity.
This is the most severe form of Pompe disease. With this type, the affected person has a complete or nearly complete lack of the enzyme necessary to process glycogen. Symptoms of classic infantile Pompe disease begin in an infant’s first three months of life and progress rapidly.
Infants with this condition will be floppy, like a rag doll, because of weak muscles. Their respiratory and heart muscles are also weak. The weak heart muscles cause most infants with this condition to die of heart failure before they are 2 years old.
Childhood or non-classic infantile
This is a slightly milder form of Pompe disease. In people with this type, the enzyme necessary to produce glycogen is reduced by 70 percent or less. Symptoms usually appear by the time a child reaches 12 months of age, but they may appear later.
Children with this condition have delayed motor skills. Muscle weakness is progressive and first affects their lower limbs followed by their respiratory muscles. The heart isn’t as severely affected as it is in the classic type of the disease.
Children with this condition often need a ventilator to help them breath. A wheelchair may be needed for mobility.
Most children with this type of Pompe disease die of respiratory failure in early childhood.
This is the mildest form of Pompe disease and accounts for two-thirds of all cases.
Symptoms may not appear until adolescence or adulthood, with some cases occurring as late as age 60.
People with this type of Pompe disease have progressive muscle weakness that leads to fatigue. Limb movement becomes difficult over time.
The lower limbs and the trunk muscles are affected, but in most cases the heart muscles aren’t affected. Spinal curvature may develop.
According to a 2006 diagnosis and management guideline for Pompe disease, about 60 percent of people with late-onset Pompe disease have a mild reduction in breathing capacity, and 30 to 40 percent have a moderate reduction.
People with late-onset Pompe disease often die as a result of respiratory failure.
What causes this condition?
Pompe disease is a genetic disorder. It’s caused by inherited mutations in a particular gene on chromosome 17 q25. The gene is responsible for producing the acid alpha-glucosidase (GAA) enzyme that processes glycogen.
When there isn’t enough GAA enzyme in a person’s body, glycogen accumulates to toxic levels in areas of cells called lysosomes. This causes muscle, tissue, and organ damage.
How is it inherited?
Pompe disease is a recessive gene disorder. If you inherit one normal gene and one defective gene for Pompe, you will be a carrier of the disease, but you won’t have symptoms.
When both parents are carriers:
- There’s a 25 percent risk that a child will be born with Pompe disease.
- There’s a 50 percent risk that a child will be born who is a carrier, like their parents.
- There is a 25 percent chance that a child will be born with normal genes.
How common is this condition?
It’s estimated that about one person in 40,000 has Pompe disease in the United States. It affects males and females alike, and all ethnic groups.
A 2006 review of the disease found that African-Americans and Chinese have a higher incidence of the infantile type. The same review found that the late-onset type of Pompe has a higher incidence in the Netherlands.
How is Pompe disease diagnosed?
Diagnosis depends on the type of symptoms and a detailed family history.
Pompe disease may be difficult to diagnose initially because it’s so rare. This is especially true for late-onset symptoms, which may resemble those of other neuromuscular diseases.
A screening chest X-ray, electrocardiogram, and echocardiogram may be used as first steps for diagnosing infants. That’s because infantile classic cases are characterized by heart damage. Levels of creatine kinase, a muscle enzyme, may also be checked.
To confirm a diagnosis, your doctor can order tests to measure the level of the GAA enzyme in dried blood spots, muscles, or skin cells. They’ll take sample tissues in a biopsy and then have those tissues cultured.
Other tests measure abnormalities in the GAA gene. This can also be useful to identify carriers.
It’s also possible to diagnose the disease in a fetus during pregnancy. A doctor may recommend this if there’s a family history of the disease. The test is done using a DNA sample of fetal cells.
Are newborns routinely screened?
Newborns in the United States are not routinely tested for Pompe disease. Through a small study, researchers found that newborn screening in a pilot program in Taiwan led to earlier diagnosis and improved survival rates.
Another study cautioned that doctors should tell parents that not all infants found with low GAA will have Pompe disease. This study also noted that the results of prenatal screening couldn’t predict the onset age of Pompe disease or its progression.
How is Pompe disease treated?
Treatment for Pompe disease depends on age and symptoms, and usually involves a team of specialists because of the complexity of the disease. In most cases, the earlier treatment begins, the better the outcome. Once muscles are damaged, they can’t be restored.
Enzyme replacement therapy
Until recently, the only treatment for Pompe disease was supportive. But in 2006, the U.S. Food and Drug Administration approved the use of ERT for all types of Pompe disease. ERT involves alpha-glucosidase acid given intravenously every two weeks. The drug, alglucosidase alfa, is sold under the brand name Lumizyme in the United States and Myozyme in other countries.
The ERT therapy has been shown to significantly improve survival rates. A 2013 review reported that when ERT is used before infants with the condition were 6 months old, the risk of death was reduced by 95 percent.
Studies show that infants in particular live longer with ERT. The treatment greatly helps the heart muscles, but it doesn’t slow the progression of the disease in other muscles. A 2014 article identified a pattern of initial improvement followed by decline and disability.
Research is ongoing into how to make ERT more effective with skeletal muscles.
Other standard treatments
As late-onset Pompe disease progresses and muscle strength declines, doctors turn to other treatments, depending on the severity of symptoms. Treatment may include:
- physical therapy to strengthen muscles for breathing, build up strength in general, and stretch muscles to prevent deformity
- breathing assistance, including ventilators
- canes, walkers, and wheelchairs to help mobility
- braces, splints, and other orthopedic appliances to also help mobility
- speech therapy when oral and breathing muscles are affected
- special diets geared to make swallowing easier
- feeding tubes to ensure adequate nutrition
- occupational therapy to promote independent functioning
- rehabilitation and counseling services for people with the condition and their family members
- surgery when necessary
What are possible complications?
ERT therapy with classic infantile Pompe disease has a possible complication in some infants of producing an immunological response that worsens the outcome. Early immunotherapy before starting ERT can help.
Later-onset Pompe disease progresses differently in each individual. Life expectancy varies depending on the extent of respiratory damage.
Later-onset Pompe disease may lead to side effects such as:
- drooping eyelids
- impaired speech
- hearing loss
- gastroesophageal reflux
A 2011 study of late-onset Pompe disease found that prior to ERT therapy, the median survival rate after diagnosis was 27 years. People who required a wheelchair or breathing assistance had a worse outlook.
What can you expect?
Pompe disease is rare and deadly. There is no cure. ERT has improved the lifespan for infants born with the disease. For those with later-onset disease, the outlook is better. The later that symptoms appear, the more slowly the disease progresses.
If you or your child have Pompe disease, you can get support and find more information about this condition through various organizations. You may also want to consider participating in clinical trials.