H2AX and amyotrophic lateral sclerosis: Among all epigenetic signals, phosphorylation of the Ser-139 residue of the histone variant H2AX (γH2AX) was upregulated in SOD1G93A mouse models, specifically in the spinal cord, frontal cortex and striatum [5], and in motor neurons of ALS patients bearing the C9orf72 repeat expansion, in comparison to normal subjects [6].