Lissencephaly child showing FISH negative and mutation in DCX gene with normal parental genetic makeup.

Lissencephaly is a clinically and genetically heterogeneous malformation of the brain, leading to a severe disabling condition and seizures. The recent discovery of molecular techniques and identification of lissencephaly genes (LIS 1 and DCX) has allowed etiologic diagnosis of this disorder. We describe a patient with lissencephaly in whom fluorescence in situ hybridization and DCX mutation analysis determined etiologic diagnosis, allowing precise genetic counseling and providing prenatal diagnosis for the family.