Lissencephaly is a disorder of brain maturation in which the brain has limited or absent gyri and sulci, resulting in a smooth brain surface. It results when early migration patterns of neurons are disrupted. The cause is not certain, but both genetic and non-genetic explanations have been hypothesized, such as viral infections during the first trimester of pregnancy, insufficient blood supply to the brain during the first trimester, damage on Chromosome 17, and recessive inheritance of a recessive gene.