D-Cysteine, which has recently been identified in the mammalian brain [52], binds to myristoylated alanine-rich protein kinase C (MARCKS) and has been proposed to be a physiological regulator of the proliferation of neural progenitor cells (NPCs) by inhibiting AKT serine–threonine protein kinase signaling mediated by FOXO1 and FOXO3a, and has been proposed to play a potential role in schizophrenia, a neurodevelopmental disorder [53]. Here, MARCKS is linked to schizophrenia.