Muscle Protein has Role in Nerve Disorders

I have so many questions about this article. What do they mean by abnormally folded myelin sheaths, in an "onion bulb" pattern? Does dystroglycan play a role in Dejerine-Sottas? Are nodes of Ranvier affected?

Each Schwann cell envelops a short stretch of axon, and the gaps between each section of the myelin sheath are called nodes of Ranvier. Ions flow through sodium channels at these nodes generating action potentials or nerve impulses. This signal is transmitted down the nerve fiber from one node to the next.
The researchers found that dystroglycan is necessary to form normal myelin sheaths. They also discovered that loss of the protein disrupts the structure of the nodes of Ranvier and affects the nerve?s ability to transmit nerve impulses. The results suggest that disruption of dystroglycan’s functions may play a role in various neuropathic disorders.
The UI team developed mice that lacked dystroglycan in their Schwann cells. This specific mutation caused progressive nerve damage in the mice. The mice were less coordinated than normal mice and their sensitivity to heat and pressure was altered. The team also showed that nerve impulses traveled more slowly in these mice.
The researchers examined the peripheral nerve fibers and saw that the myelin sheaths were abnormally folded, indicating that dystroglycan is important for normal myelination of peripheral nerve. This finding was not unexpected, as several earlier studies had suggested that dystroglycan might be involved in myelination.
However, the myelin sheath abnormalities did not seem severe enough to account for the significant reduction in the speed of nerve impulses in the mutant mice. This puzzle led the researchers to another discovery: the absence of dystroglycan appears to disrupt the normal structure of the nodes of Ranvier that are necessary to rapidly transmit nerve impulses along the nerve. In particular, loss of dystroglycan reduces the density of sodium channels that cluster at each node and are critical for normal transmission of nerve impulses.

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