Current methods for diagnosing ALS can take up to two years and rely heavily on ruling out other conditions that share similar signs and symptoms. It is believed that by the time ALS is diagnosed, therapies may be less effective as the damage to neurons is too extensive. Therefore, a better way of diagnosing ALS earlier is desperately needed.
One of the hallmarks of 97 per cent of ALS cases is the accumulation of misfolded TDP-43 protein in motor neurons. One theory is that some dying motor neurons expel misfolded TDP-43. Some of this released, misfolded TDP-43 may end up in cerebrospinal fluid. If it does, then testing cerebrospinal fluid to measure misfolded TDP-43 levels could act as a biological marker, a “biomarker,” of ALS.
With a trainee award of $165,000 funded by the ALS Canada Research Program, in partnership with Brain Canada, Dr. Yulong Sun, a postdoctoral fellow working in the lab of Dr. Avi Chakrabartty at the University Health Network in Toronto hopes to develop a new lab test that can detect misfolded TDP-43 in the cerebrospinal fluid of people with ALS.
“If we can diagnose ALS earlier, we can identify and enroll volunteers into clinical trials when the disease is still at an early stage — when therapies would have a greater chance to be effective,” said Dr. Sun. “A new lab test for detecting misfolded TDP-43 in cerebrospinal fluid could also be used as a companion diagnostic in clinical trials to measure disease progression in response to new therapies.”
Designer antibodies
Antibodies are molecules made by the body to detect foreign objects by recognizing a particular protein on the invaders. For example, when you are sick with the common cold, your body makes antibodies that recognize the protein sequence on the cold germs and attach to them like flags so that your immune cells can identify the invaders and destroy them.
Dr. Sun and his research colleagues developed some promising antibodies that can successfully detect misfolded TDP-43 in lab experiments using post-mortem brain tissue. Unlike standard antibodies that bind to any TDP-43 protein, these new antibodies only bind to the misfolded form. To validate these new antibodies, Dr. Sun will use a tool that combines them with other commercially-available antibodies that contain gold particles. This method will allow him to identify and count the clusters of misfolded TDP-43 with an advanced imaging technology called immunogold electron microscopy.
Designing a new lab test to diagnose ALS
First, Dr. Sun will test the new antibodies to see if he can detect and count misfolded TDP-43 in 40 samples of cerebrospinal fluid already collected from people with ALS through the Sunnybrook Health Sciences Centre ALS Clinic in Toronto. He will compare the results to samples from people not expected to have TDP-43 misfolding. If the antibodies can successfully detect and measure levels of misfolded TDP-43 he plans to develop a simple lab test called an immunoassay that may someday help doctors diagnose ALS earlier in the clinic and monitor disease progression.