ARX and Neurodevelopmental delay: We recently uncovered genetic and functional relationships within a set of X-linked NDD genes formed by the epigenetic eraser Lysine-Specific Demethylase 5C (KDM5C; MIM:314690) and its upstream regulators, Aristaless-related homeobox (ARX; MIM:300382), PHD Finger protein 8 (PHF8; MIM:300560) and Zinc Finger protein 711 (ZNF711; MIM:314990) [4,5].