About Pelizaeus-Merzbacher Disease (PMD)
PMD (Pelizaeus-Merzbacher disease) is a degenerative disorder caused by a mutation in the gene controlling the production of proteolipid protein (PLP), which is integral to the formation of myelin. Myelin is the substance that surrounds nerve fibers (axons) and provides the insulation necessary for proper transmission of electrical signals. Without myelin, nerve impulses are disrupted, resulting in deteriorating coordination, motor control and intellectual function.
The gene for producing PLP is found on the X chromosome. So males (who have just one X chromosome) are more likely to inherit the condition than females, who may inherit a normal X chromosome to offset the mutation in the other.
PMD symptoms typically appear in early childhood. Individuals with the milder form may have nearly normal life spans, but suffer from a decline in neurological function. The more severe form, connatal PMD, usually becomes apparent in the first few months of life. Early symptoms are often nystagmus (jerky side-to-side eye movement) and hypotonia (floppy muscle tone). Seizures and spasticity may develop as neurological function deteriorates. Severe neurological impairment, resulting in abnormal mental and physical development, is followed by premature death.
While symptoms may be mediated by medication for movement disorders, there is currently no cure or standard course of treatment.
The gene mutations responsible for PMD result in improperly produced or too much proteolipid protein (PLP), which proves toxic to oligodendrocytes, the CNS cells that produce myelin. Myelin, comprised of fats, cholesterol and protein, is critical to healthy functioning of the central nervous system because it provides the insulation needed for proper transmission of nerve impulses.
In myelination disorders, the deficient myelin sheath does not properly insulate the axon, so transmission of nerve impulses is impeded.
The StemCells Approach: Myelin Production to Protect Nerve Cells
When StemCells human neural stem cells are transplanted in animals, they migrate to the sites where myelin is deficient. They differentiate into oligodendrocytes, which form healthy myelin sheaths to protect axons, helping nerve cells communicate with each other. They do this by developing myelin appendages that wrap around the axons of nearby neurons to provide the insulation (myelin) needed for proper transmission of nerve impulses.