Leukodystrophies are a group of usually inherited disorders characterized by degeneration of the white matter in the brain. The word leukodystrophy comes from the Greek roots leuko, "white", dys, "abnormal" and troph, "growth". The leukodystrophies are caused by imperfect growth or development of the myelin sheath, the fatty insulating covering around nerve fibers. Leukodystrophies may be classified as hypomyelinating or demyelinating diseases, depending on whether the damage is present before birth or occurs after. Other demyelinating diseases are usually not congenital and have a toxic or autoimmune cause.When damage occurs to white matter, immune responses can lead to inflammation in the central nervous system (CNS), along with loss of myelin. The degeneration of white matter can be seen in an MRI scan and used to diagnose leukodystrophy. Leukodystrophy is characterized by specific symptoms including decreased motor function, muscle rigidity, and eventual degeneration of sight and hearing. While the disease is fatal, the age of onset is a key factor, as infants have a typical life expectancy of 2–8 years, while adults typically live more than a decade after onset. Treatment options are limited, although hematopoietic stem cell transplantations using bone marrow or cord blood seem to help in certain types while further research is being done.
The combined incidence of the leukodystrophies is estimated at 1 in 7,600. The majority of types involve the inheritance of an X-linked recessive, or X-linked dominant trait, while others, although involving a defective gene, are the result of spontaneous mutation rather than genetic inheritance.