Dr. Ben Wolozin explains how stress granules work.

Stress granules are the body’s way of repairing itself.  For example, if you hit your head, your body goes immediately into repair mode and creates stress granules to make the repairs. Normally, when the damage is repaired, the stress granules disperse.  This is a process that usually takes 10-15 minutes.  But, if you have a mutation or the stress granules are diseased, it makes them “stickier.” They build up and become persistent.  This is the pathology that’s found in most neurodegenerative diseases.  

The location of the persistent stress granules determines the symptoms.  Accumulation in the spinal cord results in motor dysfunction and ALS, while accumulation in the hippocampus causes memory loss and Alzheimer’s disease.