The main PAD isozymes studied to date in the brain and in neurodegenerative disorders have been PAD2 and PAD4, including in development and ageing [12], Alzheimer’s disease (AD) [13,14], amyotrophic lateral sclerosis (ALS), prion diseases and in multiple sclerosis (MS) [15,16,17,18,19,20,21], as well as in acute brain injury [22,23,24,25]. Here, PADI4 is linked to amyotrophic lateral sclerosis.