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Cerebral white matter is the compartment formed by the bundles of fibers that connect the neurons of the brain's different functional regions.
Gray matter makes up the outermost part (cortex) of the cerebrum and cerebellum, as well as the so-called "deep gray nuclei." It is primarily composed of neurons. White matter, on the other hand, is made up of axons, which are the long extensions of neurons that connect distant neurons to each other. Axons function like electrical cables; they transmit impulses and are covered by a protective sheath called myelin, which is formed by cells called oligodendrocytes. White matter also contains other important cell types called astrocytes, microglia, and ependymal cells. These cells are connected to each other, to neurons, and to vascular and meningeal structures.
The development of cerebral white matter is a complex process that occurs in the human brain from the second half of pregnancy until the end of adolescence. What happens is that first, during pregnancy, neurons settle into their final locations. Then, they gradually begin to connect with each other through short extensions (dendrites) and long ones (axons). Finally, the maturation and proliferation of oligodendrocytes and the formation of myelin take place.
White matter diseases, or "Leukoencephalopathies," are a heterogeneous group of conditions that share a common involvement of the brain's white matter. This category includes both acquired conditions (such as congenital CMV infection or the effects of perinatal distress) and hereditary conditions (such as phenylketonuria).
The term genetic leukoencephalopathies refers specifically to forms resulting from a genetic error, or a DNA-based problem. When this genetic error directly causes a malfunction of the white matter cells, the problem is considered primary.
When the white matter is affected not in a primary way, but as a consequence of a malfunction in other cells (for example, the neurons of the gray matter), the white matter problem is considered secondary.Leukodystrophies represent a subgroup of genetic leukoencephalopathies. The term leukodystrophies refers only to those genetic conditions where the cerebral white matter is affected primarily.
Main genetic leukodystrophies and leukoencephalopathies in childhood
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