Eye muscles resist ALS progression, but more research needed to understand why

Patients with amyotrophic lateral sclerosis (ALS) have intact eye muscle movement, even at more advanced stages of the disease, according to new research. However, the reason remains unknown. Researchers say that discovering how this happens may help in the design of novel treatments to fight the loss of muscle activity in ALS patients.

The research results are part of a doctoral thesis conducted by Anton Tjust from Umeå University in Sweden.

Eye muscles are very different from other muscles in the body, primarily in the connections formed between their muscular cells and neurons (called neuromuscular junctions). ALS is known to destroy motor neurons in the brain and spinal cord, thereby affecting muscular activity, but this damaging effect seems to spare the eye muscles.

“We could see that the nerve connection to the eye muscles remains intact even in stages of the disease where a large proportion of neuromuscular junctions had been lost in leg muscles,” Tjust said in a news release.

“The loss of connection between nerves and muscles can be seen in rather early stages of the degenerative process,” he explained. “We can hence establish that eye muscle protection mechanisms are active at a relatively early stage of the disease. Our results do not, however, ascertain if the disease starts in the nerve connection or in [neurons].”

Previous studies carried out by Tjust’s team to address this question showed that certain types of muscle fibers present in the eye muscles are lost as ALS progresses. Up to one-third of one of these types, known as multiply-innervated muscle fibers, are lost in certain ALS patients.

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