In<unk> , the neurons border the edge of the cleft, implying a very early disruption of the usual grey matter migration during embryogenesis. The cause of the disruption is not known, but likely the cause may be either genetic or a physical insult, such as infection, infarction, hemorrhage, in utero stroke, exposure to a toxin, or mutation. It is thought that normal neuron migration during the second trimester of intrauterine development, when primitive neuron precursors (germinal matrix) migrate from just beneath the ventricular ependyma to the peripheral hemispheres where they form the cortical grey matter. Genetic There was once thought to be a genetic association with the EMX2 gene, although this theory has recently lost support. However it has been confirmed that mutations in the COL4A1 gene occur in some patients with<unk> . In utero infections<unk>  may also be caused by environmental toxin exposure during pregnancy, infection during pregnancy (such as Cytomegalovirus), or a vascular insult. Often there are additional associated heterotopias (isolated islands of neurons) which indicate a failure of migration of the neurons to their final position in the brain caused by possible stroke.
Schizencephaly
Megalencephaly
Hemihydranencephaly
Holoprosencephaly
Hemimegalencephaly
Lissencephaly
Microlissencephaly
Microhydranencephaly