ARHGEF9 and cask-related x-linked intellectual disability: We present compelling evidence that the likely cause of XLID in this family is a missense mutation in ARHGEF9, encoding a neuronal RhoGEF known as collybistin (CB) involved in both inhibitory synaptic organization and mammalian target of rapamycin complex 1 (mTORC1) signaling pathways (Machado et al., 2015).