A diagnostic test for ALS could finally be on its way
Amyotrophic lateral sclerosis could soon be diagnosed from a muscle biopsy thanks to a possible diagnostic biomarker that’s been identified in muscle tissue.
Amyotrophic lateral sclerosis (ALS) is a progressive disease of the nervous system, which causes motor neurons to deteriorate and eventually die, leading to a loss of muscle control. Current treatment for ALS is only able to slow its progression, so it’s important to be able to diagnose the condition as soon as possible. However, there is currently no single diagnostic test for ALS and there are also no known biomarkers. Instead, doctors will look for neurological symptoms, including muscle weakness, and carry out tests to rule out other conditions like cervical spondylosis, which has similar symptoms to ALS including loss of coordination.
Recently, a research group led by Hirofumi Maruyama at the Hiroshima University (Japan), identified a protein that can be obtained from a muscle biopsy and has the potential to be used to diagnose ALS.
“Muscle is possible to biopsy, and transactive response DNA-binding protein 43 (TDP-43) accumulates in the peripheral nerves inside muscle,” explained Maruyama. “TDP-43 is a protein that plays a key role on motor neurons, and accumulation of TDP-43 may be a biomarker for early diagnosis of ALS.”
The researchers hypothesized that TDP-43 accumulation in muscle nerve bundles could be used to diagnose ALS because previous research in mice found it has an important function in axons, the part of the neuron that sends signals to other neurons. Previous research has also reported TDP-43 as a pathological protein in ALS.
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To put this theory to the test, the researchers began by looking at muscle tissue from 10 individuals who had ALS at their time of death and 12 who didn’t. They found that the muscle tissue from those with ALS had TDP-43 accumulations in their intramuscular nerve bundles, whilst the control group did not.
Following this, they performed a muscle biopsy on 114 patients with various neuromuscular diagnoses but no known family history of ALS or other muscular or neuromuscular diseases. In this group, 71 had evidence of intramuscular nerve bundles, and 33 of these individuals were found to have axonal TDP-43 accumulations within them. This group of 33 individuals was later diagnosed with ALS based on current clinical diagnostics. Of the remaining 43 people who had no evidence of intramuscular nerve bundles, only three were later diagnosed with ALS.
“Results of this dual case-control and cohort study suggest that axonal TDP-43 accumulations may be characteristic for patients with ALS, and consequently may be a novel diagnostic biomarker for ALS,” explained Maruyama. “Early diagnosis enables patients to initiate prompt treatment. We aim to prevent the progression of ALS and will continue research into developing new medication.”
