L a s t u p d a t e d J u ly 2 0 0 3
       U n i t e d L e u ko d y s t r o p hy Fo u n d a t i o n

       F AC T S H E E T:
       L E U KO DY S T RO P H Y

                                                           many different molecules that include both lipids
The leukodystrophies are a group of rare genetic dis-
                                                           (fatty molecules) and proteins. This protective sheath
orders that affect the central nervous system by dis-
                                                           acts in a manner very similar to that of the protective
rupting the growth or maintenance of the myelin
                                                           insulation that surrounds an electric wire; that is, it is
sheath that insulates nerve cells. These disorders are
                                                           necessary for the rapid transmission of electrical sig-
progressive, meaning that they tend to get worse
                                                           nals between neurons. It does this primarily by con-
throughout the life of the patient. Below we describe
                                                           taining the electrical molecules within the axon so
the source of the disorders in more detail. Fact sheets
                                                           that they are all properly transmitted to the next neu-
on the individual leukodystrophies are also available
                                                           ron. With the protective myelin coat, neurons can
from the United Leukodystrophy Foundation.
                                                           transmit signals at speeds up to 30 meters per second.
What is the nervous system?                                When the coat is damaged, the maximum speed can
                                                           decrease by ten-fold or more, since some of the sig-
In order to understand the leukodystrophies, we need
                                                           nal is lost during transmission. This decrease in speed
to discuss some basic facts about the nervous system.
                                                           of signal transmission leads to significant disruption
The nervous system is made up of two main compo-
                                                           in the proper functioning of the nervous system.
nents: the central nervous system (CNS) and the pe-
ripheral nervous system (PNS). Together, these two         What is leukodystrophy?
systems interact to carry and receive signals that are
                                                           The word leukodystrophy comes from the Greek
responsible for nearly everything we do, including in-
                                                           words leuko (meaning white), trophy (meaning
voluntary functions such as our heartbeat, and volun-
                                                           growth), and dys (meaning ill). If you put these words
tary functions such as walking.
                                                           together, the word leukodystrophy describes a set of
The CNS consists of the brain and the spinal cord,         diseases that affect the growth or maintenance of the
and contains billions of specialized cells known as        white matter (myelin).
neurons. Neurons have specialized projections called
dendrites and axons that contribute to their unique        How are the leukodystrophies different
function of transmitting signals throughout the body.      from one another?
Dendrites carry electrical signals to the neuron, while    All leukodystrophies are a result of problems with the
axons carry them away from the neuron.                     growth or maintenance of the myelin sheath. How-
The PNS consists of the rest of the neurons in the         ever, there are many genes that are important in this
body. These include the sensory neurons, which de-         process. For example, some genes are involved with
tect any sensory stimuli and alert the CNS of their        the synthesis of the proteins needed for the myelin,
presence, and motor neurons, which connect the             while others are required for the proper transport of
CNS to the muscles and carry out instructions from         these proteins to their final location in the myelin
the CNS for movement.                                      sheath that covers the axons. Defects in any of the
                                                           genes (called a mutation) may lead to a leukodystro-
What is Myelin?                                            phy. However, the symptoms of the individual leu-
Myelin, sometimes referred to as "white matter" be-        kodystrophies may vary because of the differences in
cause of its white, fatty appearance, protects and in-     their genetic cause.
sulates the axons. It consists of a protective sheath of
How do you get leukodystrophy?                             7. Aicardi-Goutieres Syndrome
                                                           8. Alexander Disease
Leukodystrophies are mostly inherited disorders,           9. Autosomal Dominant Diffure Leukoencephalo-
meaning that it is passed on from parent to child.             pathy with neuroaxonal spheroids
They may be inherited in a recessive, dominant, or X-      10. Autosomal Dominant late-onset leukoencephalo-
linked manner, depending on the type of leukodys-              pathy
trophy. The individual pages on each leukodystrophy        11. Canavan Disease
will describe the particular pattern of inheritance for    12. Cerebral Autosomal Dominant Arteropathy with
that disease. There is also a separate fact sheet de-          Subcortical Infarcts and Leukoencephalopathy
scribing the different genetic inheritance patterns            (CADASIL)
available from the United Leukodystrophy Founda-           13. Cerebrtendinous Xanthomatosis (CTX)
tion.                                                      14. Craniometaphysical dysplasia with leukoencepha-
There are some leukodystrophies that do not appear             lopathy
to be inherited, but rather arise spontaneously. They      15. Extensive Cerebral White Matter abnormality
are still caused by a mutation in a particular gene, but       without clinical symptoms
it just means that the mutation was not inherited. In      16. Familial adult-onset leukodystrophy manifesting
this case, the birth of one child with the disease does        as cerebellar ataxia and dementia
not necessarily increase the likelihood of a second        17. Familial leukodystrophy with adult onset demen-
child having the disease.                                      tia and abnormal glycolipid storage
                                                           18. Globoid Cell Leukodystrophy (Krabbe Disease)
Are the leukodystrophies related to multi-                 19. Hereditary adult onset leukodystrophy simulating
ple sclerosis?                                                 chronic progressive multiple sclerosis
The leukodystrophies do share some common fea-             20. Lipomembranous osteodysplasia with leukodys-
tures with multiple sclerosis (MS). Like the leukodys-         trophy (Nasu Disease)
trophies, MS is caused by the loss of myelin from the      21. Metachromatic Leukodystrophy (MLD)
axons. However, the cause is different; whereas leu-       22. Neonatal Adrenoleukodystrophy (NALD)
kodystrophies are generally caused by a defect in one      23. Neuroaxonal leukoencephalopathy with axonal
of the genes involved with the growth or mainte-               spheroids
nance of the myelin, MS is thought to be caused by         24. Oculodeltatoldigital Dysplasia with cerebral white
an attack on the myelin by the body’s own immune               matter abnormalities
system.                                                    25. Orthochormatic leukodystrophy with pigmented
How many different leukodystrophies are                    26. Ovarioleukodystrophy Syndrome
there?                                                     27. Pelizaeus Merzbacher Disease (X-linked spastic
New leukodystrophies are always being identified.              paraplegia)
We try to keep our information as up-to-date as pos-       28. Refsum Disease
sible, and so the 34 leukodystrophies we have listed       29. Sjogren-Larssen Syndrome
here comprise the defined leukodystrophies to the          30. Sudanophilic Leukodystrophy
best of our knowledge. Please let us know if you are       31. Vacuolating megalencephaly with subcortical
aware of any other types so that we can add them to            cysts
our list. A fact sheet on each of these diseases is        32. van der Knaap Syndrome (Vacuolating Leu-
available from the United Leukodystrophy Founda-               kodystrophy with Subcortical Cysts)
tion.                                                      33. Vanishing White Matter Disease (Childhood
1. 18q Syndrome with deficiency of myelin basic                ataxia with diffuse central nervous system hypo-
    protein                                                    myelination, or CACH)
2. Acute disseminated encephalomyeolitis (ADEM)            34. Zellweger Syndrome (ZS)
3. Acute Disseminated Leukoencephalitis
4. Acute Hemorrhagic Leukoencephalopathy
5. Adrenoleukodystrophy (ALD)
6. Adrenomyeloneuropathy (AMN)

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