Amyotrophic lateral sclerosis (ALS) is a fatal human neurodegenerative disease 
affecting primarily motor neurons. Two RNA-binding proteins, TDP-43 and FUS, 
aggregate in the degenerating motor neurons of ALS patients, and mutations in 
the genes encoding these proteins cause some forms of ALS. TDP-43 and FUS and 
several related RNA-binding proteins harbor aggregation-promoting prion-like 
domains that allow them to rapidly self-associate. This property is critical for 
the formation and dynamics of cellular ribonucleoprotein granules, the crucibles 
of RNA metabolism and homeostasis. Recent work connecting TDP-43 and FUS to 
stress granules has suggested how this cellular pathway, which involves protein 
aggregation as part of its normal function, might be coopted during disease 
pathogenesis.