The leukodystrophies are a group of over 50 rare genetic disorders that affect the central nervous system by disrupting the growth or maintenance of the myelin sheath that insulates nerve cells. Myelin is commonly referred to as the brain's white matter. Myelin covers nerve cells and ensures the clear transmission of nerve impulses from one part of the body to another. These disorders are progressive, meaning that they tend to get worse throughout the life of the patient.

The word leukodystrophy comes from the Greek words leuko (meaning white), trophy (meaning growth), and dys (meaning ill). If you put these words together, the word leukodystrophy describes a set of diseases that affect the growth or maintenance of the white matter (myelin).

Leukodystrophies differ from multiple sclerosis (MS) in that leukodystrophies are caused by a defect in the genes involved with growth or maintenance of the myelin while MS is believed to be caused by an attack on the myelin by the body's own immune system.