SYTL4 and Macrocephaly: Their dysfunction through mutations has been shown to play a crucial role in causing diverse patho-physiologies including X-linked mental retardation associated with autism, epilepsy, and macrocephaly, suggesting a major role for specific RAB-binding effector proteins, such as the SYTL4, and interacting RAB-activating GTPases (RAB- GTPases) in the maintenance of normal neuronal function [51,52,59,60,61,66,67].