People with multiple sclerosis (MS) are three to six times more likely to develop epilepsy than the general population, a study says.
Researchers believe the loss of myelin in certain neurons — a hallmark of MS — is what causes the seizures.
The myelin sheath is a coating that protects neurons. It is progressively lost in MS due to a malfunctioning immune system attacking and destroying it. Myelin degeneration destabilizes neuron function and ultimately leads to cell death, contributing to disease progression and disability in MS patients.
Neurons known as parvalbumin interneurons are responsible for preventing hyperactivity. In MS, these neurons lose their myelin protection, affecting their activity in the brain. Researchers believe this loss causes seizures.
“Demyelination causes damage to axons and neuronal loss — specifically, parvalbumin interneurons are lost in mice, hyperactivity is no longer down but up, and this could be a cause of seizures,” Seema Tiwari-Woodruff, the study’s senior author, said in a news release. “It’s very likely this is what is occurring in those patients with MS who are experiencing seizures.”
Researchers studied myelin loss by feeding mice with food containing cuprizone, a compound that damages myelin-producing cells called oligodendrocytes. After nine weeks of the diet, most mice started to have seizures.
“Without myelin, axons are vulnerable,” Tiwari-Woodruff said. “They develop blebs – ball-like structures that hinder transport of important proteins and conduction of electrical signals. In some instances, significant [neuronal] damage can lead to neuronal loss. In both MS and our mouse model, parvalbumin interneurons are more vulnerable and likely to die. This causes the inhibition to be removed and induce seizures.” This means that “neuronal survival may be directly tied to the trophic support provided by myelin.”
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