 Progressive bulbar palsy patients that have this mutation are classified with FALS patients, Familial ALS (FALS) accounts for about 5%-10% of all ALS cases and is caused by genetic factors.Within these, about 20–25% are linked to the "SOD1" mutation.It is not currently known if and how the decreased "SOD1" activity contributes to Progressive Bulbar Palsy or FALS, and studies are being done in patients and transgenic mice to help further understand the impact of this gene on the disease.