What else is it called?
- GALC deficiency
- Galactocerebrosidase deficiency
- Galactosylceramidase deficiency
- Globoid Cell Leukodystrophy
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What causes it?
Krabbe disease is caused by mutations of the GALC gene. This gene creates an enzyme to break down fats called galactolipids. In absence of this enzyme, these fats cannot be broken down, and they accumulate and form globoid cells (large cells which usually have more than one nucleus). This causes damage to the cells which create myelin, reducing the ability of nerves to transmit signals around the body and leading to the symptoms of Krabbe disease.
Myelin is the insulation material that is made from proteins and lipids (fats etc) that is produced in the neuron to coat and protect the transmission arm of the neuron – the axon. This process is called myelination. Myelin is a spongy substance which is white in appearance and is referred to as ‘the white matter’ of the brain. The major purpose of the myelin is to increase the speed of transmission of an impulse. When this process is disrupted or destroyed by a dysfunctional metabolic process, with a genetic cause it can be classified as a leukodystrophy.
How common is it?
This disorder is estimated to affect approximately 1/100,000 in the Northern European population. The infantile form is the most common form in Northern Europe, accounting for 85%-90% of cases. Elsewhere in the world, it occurs in approximately 1/100,000 to 1/250,000 live births. There is a high incidence in some isolated communities in Israel where the prevalence is reported to be 6 cases per 1,000 people.
What are the signs and symptoms?
This is a severe form of Lysosomal storage disorder that results in progressive damage to the nervous system.
The infantile form of Krabbe Disease is the most common and most severe; symptoms are irritability, feeding difficulties, stiff posture, hypotonia and episodes of fever with no sign of infection. Vision and hearing loss and seizures follow, and mental and physical development is delayed. Progressive muscle weakness makes moving, chewing, swallowing and breathing increasingly difficult, and those affected rarely live past the age of 2.
Late-onset forms can begin anytime from childhood to adulthood. Symptoms can vary but commonly begin with walking difficulties and vision loss. Other symptoms can include seizures and intellectual regression. Those with late-onset Krabbe disease can survive for many years with the condition.
How is it diagnosed?
Diagnosis may be determined by the acknowledgement of physical symptoms, a patient and family history, and a range of specialised tests including blood and urine analysis, an electroencephalogram (EEG) and brain MRI scan. Genetic testing and enzyme assays can confirm diagnosis.
Can it be treated?
Although there is no known cure for Krabbe disease, haemopoietin stem cell transplant has been shown to benefit cases early in the course of the disease. Generally, treatment for the disorder is symptomatic and supportive. Physical therapy may help maintain or increase muscle tone and circulation. Cord blood transplants from unrelated donors have been successful in stopping the disease as long as they are given before overt symptoms appear.
Do my family need to be tested?
Humans have chromosomes composed of DNA. Genes are pieces of DNA that carry the genetic instruction. Each chromosome may have several thousand genes.
The word mutation means a change or error in the genetic instruction.
We inherit particular chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instruction that determines characteristics, which are a combination of the parents.
This is an inherited condition. There is nothing that could have been done to prevent your baby from having this condition.
Everyone has a pair of genes that make the enzyme needed to break down galactolipids. In children with this disorder, neither of these genes works correctly. These children inherit one non-working gene from each parent.
Parents of children with this disorder are termed as carriers of the condition. Carriers do not have the disorder because the other gene of this pair is working correctly. This disorder is autosomal recessive.
When both parents are carriers, in each pregnancy the risk to the baby is as follows:
- There is a 25% chance (1 in 4) of the baby having the disorder.
- There is a 50% chance (1 in 2) for the baby to be a carrier of the disorder.
- There is a 25% chance (1 in 4) for the baby to have two working genes and neither have the disorder nor be a carrier