SMARD is a disease that affects nerve cells. These are the cells that relay information from the brain through the spinal cord to different muscles in your body. This is kind of like the wires in your house that transfer electricity from a light switch to the light that you want to turn on.
The nerves relaying this information die, causing a breakdown in this system. Without this flow of information, patients cannot control their muscles and they become unable to move or paralyzed so their muscles waste away. This wasting away is also called atrophy.
What makes this disease different from other diseases that result in paralysis is that it also affects the nerves helping to control the muscle at the bottom of your rib cage that helps you breathe.
As a result, the patients have difficulty breathing which is also called respiratory distress. That is why the full name of SMARD is Spinal Muscular Atrophy with Respiratory Distress.
This typically occurs in children six weeks to six months of age, and it is all caused by changes in a single piece of DNA.
To better study this disease, we use a mouse that has changes in the same piece of DNA and gets symptoms very similar to what we see in human patients.
By fixing only the nerves in these mice, we are able to prevent paralysis. These mice can move normally, but surprisingly they still died at a young age.
This is because the stress on their heart from being able to move made the heart cells get sick and died which produced a heart full of scar tissue that was unable to pump blood. If we fix both the heart and the nerves, the mice live a long and healthy life.
My work focuses on understanding the similarities and differences between what goes on in the heart and the nerves in this disease to develop therapies that treat all aspects of SMARD.
Amy Hicks, Ph.D., is a postdoctoral associate working in The Cox Lab at The Jackson Laboratory. Connect with her on Twitter @AMouse3000.