Among them, the Doublecortin (Dcx) MAP (Francis et al., 1999; Gleeson et al., 1999), also involved in type 1 lissencephaly, when inactivated in mouse generates a striking anatomical defect, mainly restricted in the CA3 region, with an abnormal double layer of pyramidal neurons. The gene discussed is DCX; the disease is classic lissencephaly.