The term leukodystrophy is used for a group of rare genetic diseases that involve the brain and/or spinal cord’s white matter. Currently, over 40 different leukodystrophies have been described.
The brain's white matter consists of axons, the "cables" that build up a complex network of connections between different nerve cells. These axons are wrapped by a thick insulating membrane, referred to as myelin, which is important for the isolation and protection of axons. Leukodystrophies are diseases in which a gene defect leads to abnormalities of either the axon, the myelin, or the cells that provide nutrients to the axon.
Currently, over 40 different leukodystrophies have been described. These are, by definition, progressive diseases, meaning that the disease gets worse throughout a lifetime. Some of these diseases start in early infancy, progress rapidly, and are fatal, while others only affect adults or progress slowly over decades. In addition, some leukodystrophies can present either during childhood or adulthood. Diagnostic evaluation is usually based on Magnetic Resonance Imaging (MRI), clinical hallmarks, and different metabolic or genetic tests. Due to the rarity of these diseases, patients are often misdiagnosed as having multiple sclerosis or other neurologic diseases.
Treatment for leukodystrophies can be grouped into disease-specific therapy, such as correcting the genetic or metabolic defect, or symptomatic therapy, such as treating muscle stiffness or seizures. While some of these rare diseases have become treatable, for most leukodystrophies, no disease-specific therapy exists.
Examples of Leukodystrophies:
- Adrenoleukodystrophy
- Alexander Disease
- Canavan Disease
- Cerebrotendinous Xanthomatosis
- Krabbe Disease (globoid cell leukodystrophy)
- Metachromatic Leukodystrophy
- Pelizaeus-Merzbacher Disease
- Vanishing White Matter Leukodystrophy
Undiagnosed Leukodystrophies: Despite advances in neuroimaging and genomic medicine, in about half of all patients who are diagnosed with a leukodystrophy, the genetic basis is not yet known. In this case, the term ”undiagnosed leukodystrophy” is used. At Kennedy Krieger Institute, we have had an active program for the identification of these rare cases for over 20 years. We currently utilize whole exome sequencing to discover the genes involved in these diseases.