Leukodystrophy describes a collection of about 15 rare genetic disorders that effect the brain, spinal cord and peripheral nerves. It is characterized by imperfect growth or development of the white matter covering nerve fibers in the brain.
Leukodystrophy comes from the Greek words leuko meaning white (referring to the white matter of the nervous system) and dystrophy meaning imperfect growth or development. The white matter is called the myelin sheath and is an extremely complex substance composed of at least 10, and probably more, chemicals. The myelin sheath protects the axon (a long and single-nerve cell process that acts as a wire to conduct impulses away from the cell body), much the way insulation does to an electric wire.
Each type of leukodystrophy affects one of these chemicals. Leukodystrophies covered in this essay are Alexander's disease, childhood ataxia with central nervous system hypomyelination (CACH), also known as vanishing white matter disease, cerebralautosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), cerebrotendinous xanthomatosis (CTX), metachromatic leukodystrophy, ovarioleukodystrophy syndrome, and Van der Knapp syndrome, also called vacuolating leukodystrophy with subcortical cysts.
Leukodystrophies covered as separate entries in this encyclopedia are adrenoleukodystrophy (ALD)/adrenomyeloneuropathy (AMN), Aicardi-Goutieres syndrome, canavan disease (spongy degeneration), Krabbe disease (globoid cell leukodystrophy), neonatal adrenoleukodystrophy, Pelizaeus-Merzbacher disease (X-linked spastic paraplegia), Refsum disease, and Zellweger syndrome.
Genes are the blueprint for the human body that directs the development of cells and tissue. Mutations in
All of the leukodystrophies discussed in this article have an autosomal recessive pattern of inheritance that affects males and females. People with only one abnormal gene are carriers but since the gene is recessive, they do not have the disorder. Their children will be carriers of the disorder but not show symptoms of the disease. Both parents must have one of the abnormal genes for a child to have symptoms of an autosomal recessive leukodystrophy. When both parents have the abnormal gene, there is a 25% chance each child will inherit both abnormal genes and have the disease. There is a 50% chance each child will inherit one abnormal gene and become a carrier of the disorder but not have the disease itself. There is a 25% chance each child will inherit neither abnormal gene and not have the disease nor be a carrier.
All of the leukodystrophies discussed here appear to affect all racial and ethnic groups and all geographic populations. However, metachromatic leukodystrophy has been found in a higher frequency in highly inbred groups, such as the Habbanite Jewish population. Van der Knapp syndrome has a high prevalence among Turkish and Asian-Indian people.
The most common signs seen in most leukodystrophies include gradual changes in an infant or child who previously appeared healthy. These changes may appear in body tone, movements, gait, speech, the ability to eat, hearing, vision, behavior, and memory. Specific signs and symptoms for individual leukodystrophies include:
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Author Info: Ken R. Wells, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Genetic Disorders Part I, 2002 |