A locus for bilateral perisylvian polymicrogyria maps to Xq28.

Polymicrogyria (PMG) is one of a large group of human cortical malformations that collectively account for a significant percentage of patients with epilepsy, congenital neurological deficits, and intellectual disability. PMG is characterized by an excess of small gyri and abnormal cortical lamination. The most common distribution is bilateral, symmetrical, and maximal, in the region surrounding the sylvian fissures, and is known as "bilateral perisylvian polymicrogyria" (BPP).

Clinical and molecular basis of classical lissencephaly: Mutations in the LIS1 gene (PAFAH1B1).

Classical lissencephaly (LIS) and subcortical band heterotopia (SBH) are related cortical malformations secondary to abnormal migration of neurons during early brain development. Approximately 60% of patients with classical LIS, and one patient with atypical SBH have been found to have deletions or mutations of the LIS1 gene, located on 17p13.3.