RAB-binding GTPases play a crucial role in causing diverse patho-physiologies including X- linked mental retardation (intellectual disability) associated with autism, epilepsy, and macrocephaly, suggesting a major role for specific RAB-binding effector proteins, such as SYTL4, and interacting RAB-activating GTPases (RAB GTPases) in the maintenance of normal neuronal function [51,59,60,61,64,65,66];. This evidence concerns the gene SYTL4 and Macrocephaly.