What is Krabbe Disease?
Krabbe disease is a rare and usually deadly disorder of the nervous system. It is an inherited genetic disease, which means that it is passed down in families. People with Krabbe disease are not able to create enough of a substance called galactosylceramidase, which is needed to make myelin. Myelin is a material your body uses to surround and protect nerve fibers. Without this protection, cells in the brain die, and the nerves in the brain and other parts of the body do not work properly.
Krabbe disease is seen mostly in infants, but it can also develop later in life. Unfortunately, right now there is no cure for Krabbe disease, and most infants with this disease will die before age 2.
What Causes Krabbe Disease?
Krabbe disease is a genetic disorder, which means that a person inherits the disease from his or her parents. It is caused by a genetic mutation—a permanent change in the DNA sequence that makes up a certain gene. The mutation affects the message that the gene sends to the cells in your body. The gene for Krabbe disease can be found on chromosome 14. A child needs to get an abnormal gene from both parents to inherit the disease.
The abnormal gene results in a shortage of an important enzyme that your body needs called galactosylceramidase (GALC). Your body needs GALC to make and maintain myelin, a substance that surrounds and helps protect your nerves.
In people with Krabbe disease, who do not have GALC, a substance called galactolipids will build up in the brain. Galactolipids are stored by cells called globoid cells. For this reason, Krabbe disease is sometimes also called globoid cell leukodystrophy.
There are two types of Krabbe disease:
- Early-onset Krabbe disease occurs in the first months after birth, typically before an infant reaches 6 months of age.
- Late-onset Krabbe disease occurs later in childhood or in early adolescence.
Who Is at Risk for Krabbe Disease?
Krabbe disease is very rare. According to the Mayo Clinic, the disease affects about one in every 100,000 people in the United States (Mayo Clinis, 2011). It occurs most frequently in people of Scandinavian descent.
A child has a one in four chance of developing the disorder if both parents have the defective gene.
What Are the Symptoms of Krabbe Disease?
Generally, the younger the age of onset of Krabbe disease, the faster the disease will progress. People who develop Krabbe disease later in life may have less severe symptoms than infants who get the disease.
Early-Onset Krabbe Disease
Symptoms of early-onset Krabbe disease include
- feeding problems
- loss of head control
- irritability and excessive crying
- poor coordination of movement or stiffness
- severe seizures
- spasms or jerking of the arms and legs
- changes in muscle tone
- deterioration of mental and motor function
- deafness and blindness
Late-Onset Krabbe Disease
Symptoms of late-onset Krabbe disease in older children and adolescents include
- progressive loss of vision leading to blindness
- difficulty walking
- muscle weakness or rigid muscles
How Is Krabbe Disease Diagnosed?
A healthcare provider will conduct a physical exam to look for symptoms. The healthcare provider will take a sample of blood or skin and send it to a laboratory for analysis. The laboratory can test for GALC enzyme activity in the sample. If GALC activity levels are very low, the child may have Krabbe disease.
The following tests may also be performed to confirm a diagnosis:
- imaging scans (MRI) of the brain to look for abnormalities. However, a scan may appear normal in the early stages of the disease.
- nerve conduction studies to measure the speed at which electrical impulses are sent through the nervous system. The speed of nerve conduction will be slower if myelin is impaired.
- eye examination to look for signs of damage to the optic nerve
- genetic testing to detect the genetic defect that causes Krabbe disease. Genetic testing can be done before a child is born. Using a needle, a doctor will withdraw amniotic fluid from the mother and send the sample to a laboratory for testing. A prenatal diagnostic test is recommended if any other members of your family have the condition.
How Is Krabbe Disease Treated?
There is no cure for Krabbe disease. However, the following treatments may be given to patients to help alleviate their symptoms:
- anticonvulsant medication to stop seizures
- drugs to help ease muscle spasms
- physical therapy to help slow deterioration of muscles
- occupational therapy to help older children with common tasks, such as getting dressed and eating
Research has found two procedures that may have an effect on the progression of Krabbe disease, rather than just treating the symptoms: bone marrow transplantation (also called hematopoietic stem cell transplantation) and cord blood transplantation. During these procedures, a person with Krabbe disease will receive cells from a healthy person. The new cells are able to make the GALC enzyme that the patient could not make on his or her own. Both of these procedures have risks of their own.
Bone Marrow Transplantation
An adult will donate some bone marrow (a material found in bones) to replace the bone marrow in the child who has Krabbe disease. The best results have been only in patients with late-onset Krabbe disease who have been treated before severe symptoms develop. It has not been helpful in infants with early-onset Krabbe disease who have already developed symptoms.
Cord Blood Transfusion
A doctor will transfuse cord blood stem cells into the patient. The cells are obtained from the umbilical cord of a donor who is not related to the patient. However, this procedure has also been shown to help only those patients treated before symptoms appear.
What Are the Complications of Krabbe Disease?
The disease is usually life threatening. Since it damages a person’s central nervous system, complications include:
- severe loss of muscle tone
- severe mental deterioration
- respiratory failure and death
What Is the Long-Term Outlook for People With Krabbe Disease?
The outlook is very poor. On average, infants who develop Krabbe disease will die before age 2. Children who develop the disease later in life will live a bit longer, but typically die between 2 and 7 years after they are diagnosed.
How Can Krabbe Disease Be Prevented?
If both parents carry the genetic defect that causes Krabbe disease, there is a 25 percent chance of passing the disease to their child. The 25 percent risk of passing on the disease cannot be lowered if parents both carry the genetic mutation—the only way to avoided the risk if the carriers decide to not have children. The parents can, however, find out if they carry the gene for Krabbe disease through a blood test.
If there is a family history of Krabbe disease, prenatal tests can be done to screen the fetus for the condition. Genetic counseling is recommended for people with a family history of Krabbe disease if they are considering having children.