Therefore, it is possible that neurons re-enter the G1 phase of the cell cycle in Parkinson’s disease (PD) and amyotrophic lateral sclerosis due to the accumulation of hyperphosphorylated pRb (retinoblastoma protein) in neurons and changes in the location of the E2F1 transcription factor [41,42]. Here, E2F1 is linked to Parkinson disease.