Pedigree of families with novel mutations in the ARX homeodomain. Open symbols represent normal individuals, filled symbols represent affected individuals as per the key. Proband indicated with arrow. Individual generations are numbered with Roman numerals. MRI findings in proband of family 1 (a) sagittal T1 MR sequence demonstrates lissencephaly P > A and marked lateral ventriculomegaly. Note subependymal cysts (large arrow) abnormal periventricular white matter signal (small arrow) and abnormal basal ganglia signal clear arrow, (b) sagittal T1 MR sequence of the midline demonstrates agenesis of the corpus callosum and (c) axial T2 MR sequence demonstrates colpocephaly and lissencephaly with transition from posterior agyria (solid arrow) to anterior pachygyria (open arrow).