Various forms of Classical lissencephaly (also called type I lissencephaly) include anomalies in the LIS1 gene (isolated lissencephaly and Miller-Dieker syndrome (MDS), anomalies in the TUBA3 and DCX genes, and lissencephaly caused by mutations in the ARX gene (XLAG syndrome, X-linked lissencephaly with agenesis of the corpus callosum). Here, ARX is linked to lissencephaly spectrum disorders.