Causes of Myelination

Myelination is the formation of myelin, a white, fatty substance that coats nerve cells and forms an insulating sheath. Myelin sheaths allow the conduction of signals or impulses between our brains and the rest of the cells in our bodies. There are a number of demyelinating disorders in which myelin is damaged, resulting in a disruption of these signals and causing a variety of neurological symptoms.

Production

• Myelin is composed of lipids (fats) and proteins. According to the National Multiple Sclerosis Society, there are two different types of myelin, distinguished by both their chemical composition and location within the body. In the central nervous system or CNS, which is composed of the brain and spinal cord, myelin is produced by specialized nerve cells called oligodendrocytes. The peripheral nervous system or PNS is made up of motor and sensory neurons which conduct signals from the CNS to the rest of the body. In the PNS, myelin is produced by Schwann cells. Myelin produced in the CNS differs from that produced in the PNS chemically, but they are functionally the same.

Development

• Myelination begins during the third trimester of gestation, and continues for several years after birth. There are several neurological developmental milestones that doctors track in a child's first 24 months, and these correspond to the patterns of myelin formation, according to the University of Utah Health Sciences Library.

Hereditary Disorders

• Hereditary demyelinating disorders occur when myelin fails to develop properly or becomes damaged. These diseases can affect either the CNS or the PNS. Hereditary disorders in the CNS include the leukodystrophies, which are diseases that usually present in childhood and progress quickly leading to paralysis and death, according to the Myelin Project. Marie-Charcot-Tooth Disease, or MCT, is an example of a demyelinating disorder of the PNS. MCT often causes foot and joint deformities.

Acquired Disorders

• The most common acquired demyelinating disorder in the CNS is multiple sclerosis or MS, which affects 400,000 people in the U.S. and 2.5 million people worldwide, according to the National Multiple Sclerosis Society. Guillain-Barré Syndrome is one example of an acquired disorder in the PNS. In both CNS and PNS acquired disorders, it is believed that myelin damage is the result of an autoimmune attack, in which the body suddenly fails to recognize myelin as part of itself. The cause of these autoimmune attacks is unknown.

Myelin Repair

• When myelin is damaged as the result of disease, the body is capable of repair. In the CNS, oligodendrocytes are signaled to begin production of new myelin at the damage site. The mechanism for this signaling is not well understood, but is the subject of ongoing research projects, according to the National Multiple Sclerosis Society. In the PNS, production of myelin is started by a migration of Schwann cells to the area of damage. Repair mechanisms become less effective when sites are subjected to repeated myelin damage, resulting in permanent damage.