Leukodystrophy

Leukodystrophy refers to a group of disorders characterized by progressive degeneration of the white matter of the brain. The leukodystrophies are caused by imperfect growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fibers. Myelin, which lends its color to the white matter of the brain, is a complex substance made up of at least ten different molecules. Each of the leukodystrophies is the result of a defect in the gene that controls the production or metabolism of one (and only one) of the component molecules of myelin.
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Leukodystrophy /leu·ko·dys·tro·phy/ disturbance of the white substance of the brain; see also leukoencephalopathy. [more]Leukodystrophy - Community and Resources

Disorder of the white matter of the brain. The white matter mainly consists of nerve fibers (not the nerve cells themselves) and is concerned with conduction od nerve impulses.