<P> Unmyelinated fibers and myelinated axons of the mammalian central nervous system do not regenerate . </P> <P> Some studies have revealed that optic nerve fibers can be regenerated in postnatal rats . This regeneration depends upon two conditions: axonal die - back has to be prevented with appropriate neurotrophic factors, and neurite growth inhibitory components have to be inactivated . These studies may lead to further understanding of nerve fiber regeneration in the central nervous system . </P> <P> Demyelination is the loss of the myelin sheath insulating the nerves, and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis, acute disseminated encephalomyelitis, neuromyelitis optica, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, Guillain--Barré syndrome, central pontine myelinosis, inherited demyelinating diseases such as leukodystrophy, and Charcot - Marie - Tooth disease . Sufferers of pernicious anaemia can also suffer nerve damage if the condition is not diagnosed quickly . Subacute combined degeneration of spinal cord secondary to pernicious anaemia can lead to slight peripheral nerve damage to severe damage to the central nervous system, affecting speech, balance, and cognitive awareness . When myelin degrades, conduction of signals along the nerve can be impaired or lost, and the nerve eventually withers . A more serious case of myelin deterioration is called Canavan disease . </P> <P> The immune system may play a role in demyelination associated with such diseases, including inflammation causing demyelination by overproduction of cytokines via upregulation of tumor necrosis factor or interferon . </P>

Which disease is caused by the breakdown of the myelin sheath that surrounds the axon of the neuron
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