DCX and Lissencephaly: In humans, the Dcx gene is located on chromosome X. It is indispensable for brain development and specifically for migration of immature neurons, such that lack of functional DCX manifests in gray matter heterotopia (females) or lissencephaly (smooth brain; males), causing various degrees of intellectual disability and epilepsy (Gleeson et al, 1998; des Portes et al, 1998).