Krabbe (KRAH-buh) disease is an inherited disorder that destroys the protective coating (myelin) of nerve cells in the brain and throughout the nervous system.
In most cases, signs and symptoms of Krabbe disease develop in babies before 6 months of age, and the disease usually results in death by age 2. When it develops in older children and adults, the course of the disease can vary greatly.
There's no cure for Krabbe disease, and treatment focuses on supportive care. However, stem cell transplants have shown some success in infants who are treated before the onset of symptoms and in some older children and adults.
Krabbe disease affects about 1 in 100,000 people in the United States. It is also known as globoid cell leukodystrophy.
In most cases, the signs and symptoms of Krabbe disease appear during the first 2 to 5 months of life. They begin gradually and progressively worsen.
Common signs and symptoms early in the course of the disease include the following:
As the disease progresses, signs and symptoms become more severe. They may include:
When Krabbe disease develops later in childhood or during adulthood, signs and symptoms can vary widely. They may include:
As a general rule, the younger the age that Krabbe disease occurs, the faster the disease progresses and the more likely it is to result in death.
Some people diagnosed during adolescence or adulthood may have less severe symptoms, with muscle weakness as a primary condition. They may have no impairment of their thinking skills.
The early signs and symptoms of Krabbe disease in infancy can indicate any number of diseases or developmental problems. Therefore, it's important to get a prompt and accurate diagnosis if your child is experiencing any signs or symptoms of the disease.
Signs and symptoms most often associated with older children and adults also are not specific to Krabbe disease and require a timely diagnosis.
Krabbe disease is caused when a person inherits two copies of an altered (mutated) gene — one copy from each parent.
A gene provides a kind of blueprint for producing proteins. If there is an error in this blueprint, then the protein product may not work properly. In the case of Krabbe disease, two mutated copies of a particular gene result in little or no production of an enzyme called galactocerebrosidase (GALC).
Enzymes, such as GALC, are responsible for breaking down certain substances in a cell's recycling center (lysosome). In Krabbe disease, the short supply of GALC enzymes results in the accumulation of certain types of fats called galactolipids.
Galactolipids normally exist in cells that produce and maintain the protective coating of nerve cells (myelin). However, an abundance of galactolipids has a toxic effect. Some galactolipids trigger myelin-forming cells to self-destruct.
Other galactolipids are taken up by specialized debris-eating cells in the nervous system called microglia. The process of cleaning up excessive galactolipids transforms these normally helpful cells into abnormal, toxic cells called globoid cells, which promote myelin-damaging inflammation.
The subsequent loss of myelin (demyelination) prevents nerve cells from sending and receiving messages.
The gene mutation associated with Krabbe disease only causes the disease if two mutated copies of the gene are inherited. A disease resulting from two mutated copies is called an autosomal recessive disorder.
If each parent has one mutated copy of the gene, the risk for a child would be as follows:
Genetic testing to understand the risk of having a child with Krabbe disease may be considered in certain situations:
Genetic testing should be carefully considered. Ask your doctor about genetic counseling services that can help you understand the benefits, limits and implications of genetic testing.
To have an autosomal recessive disorder, you inherit two mutated genes, one from each parent. These disorders are usually passed on by two carriers. Their health is rarely affected, but they have one mutated gene (recessive gene) and one normal gene (dominant gene) for the condition. Two carriers have a 25% chance of having an unaffected child with two normal genes (left), a 50% chance of having an unaffected child who also is a carrier (middle), and a 25% chance of having an affected child with two recessive genes (right).
A number of complications — including infections and respiratory difficulties — can develop in children with advanced Krabbe disease. In the later stages of the disease, children become incapacitated, are confined to their beds and eventually lapse into a vegetative state.
Most children who develop Krabbe disease in infancy die before the age of 2, most often from respiratory failure or complications of immobility and markedly decreased muscle tone. Children who develop the disease later in childhood may have a somewhat longer life expectancy, usually between two and seven years after diagnosis.
Your doctor will conduct a general physical exam and assess signs and symptoms that may indicate a neurological disease. A diagnosis of Krabbe disease is based on a series of tests, which may include the following.
A blood sample will be sent to a laboratory to assess the level of GALC enzyme activity. Very low or no GALC activity level may indicate Krabbe disease.
Although the results help a doctor make a diagnosis, they don't provide evidence of how quickly the disease may progress. For example, very low GALC activity doesn't always mean that the condition will advance rapidly.
Your doctor may order one or more imaging tests that can detect the loss of myelin (demyelination) in affected regions of the brain. These may include:
A nerve conduction study assesses the rate at which nerves conduct a signal — essentially how quickly they can send a message. A special device measures the time it takes an electrical impulse to travel from one point on the body to another. When myelin is impaired, nerve conduction is slower.
A genetic test may be done with a blood sample to confirm a diagnosis. There are variant forms of the mutated gene that results in Krabbe disease. The particular type of mutation may provide some clues regarding the expected course of the disease.
In some states, a screening test for Krabbe disease is part of a standard set of assessments for newborns. The initial screening test measures GALC enzyme activity. If the enzyme activity is found to be low, follow-up GALC tests and genetic tests are conducted.
The use of newborn screening tests is relatively new. Researchers are still working to understand how best to use these tests, how well the tests lead to an accurate diagnosis and how well they predict the course of the disease.
Studies to date suggest that identifying markers for Krabbe disease before symptoms appear may create a unique treatment window. A treatment procedure called stem cell transplantation may improve the course of Krabbe disease when administered in the first weeks of life.
For infants who have already developed symptoms of Krabbe disease, there is currently no treatment that can change the course of the disease. Treatment, therefore, focuses on managing symptoms and providing supportive care. Interventions may include the following:
Interventions for older children or adults with less severe forms of the disease may include:
Hematopoietic stem cells are specialized cells that can develop into all of the different types of blood cells in the body. These stem cells are also the source of microglia, specialized debris-eating cells that take up residence in the nervous system. In Krabbe disease, microglia are transformed into toxic globoid cells.
In stem cell transplantation, donor stem cells are delivered into the recipient's bloodstream through a tube called a central venous catheter. The donor stem cells help the body produce healthy microglia that can populate the nervous system and deliver functioning GALC enzymes. This treatment may help restore some degree of normal myelin production and maintenance.
This therapy may improve outcomes in infants if treatment begins before the onset of symptoms — that is, when a diagnosis results from a newborn screening test. Current evidence suggests that stem cell transplantation is most effective when started before an infant reaches 2 weeks of age.
Studies have found that pre-symptomatic children treated with stem cell transplantation may have slower disease progression and improved quality — and length — of life, compared with children who don't receive stem cell transplantation before symptoms develop. However, infants who have stem cell transplants before symptoms appear still develop significant difficulties with speech, walking and other motor skills during childhood.
Older children and adults with mild symptoms of Krabbe disease also may benefit from this treatment. As with infants, the severity of symptoms at the time of stem cell transplantation affects treatment outcomes.
Organizations that offer support, educational resources, networking opportunities and services to families dealing with Krabbe disease include the following:
United Leukodystrophy Foundation
In some cases, Krabbe disease is diagnosed in newborns with screening tests before symptoms appear. Conversations with your child's doctor and a specialist in nervous system disorders (neurologist) would begin as soon as a diagnosis is confirmed. In most cases, however, the onset of symptoms triggers an exploration of possible causes.
It's important to take your child to all regularly scheduled well-baby visits and annual appointments during childhood. These visits are an opportunity for your child's doctor to monitor your child's development in key areas, including:
Questions you should be prepared to answer during regular checkups might include the following:
If you're seeing your doctor because of the recent onset of symptoms, you'll likely start by seeing your general practitioner or your child's pediatrician. After an initial evaluation, your doctor may refer you to a neurologist.
Be prepared to answer the following questions about your symptoms or on your child's behalf:
Questions especially for older children or adults may include: