Polymicrogyria

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Polymicrogyria (abbrev. PMG, also known as cobblestone lissencephaly or microgyria) is a neurodevelopmental disorder with abnormal gyrification of the cerebral cortex. Instead of the few and large convolutions (gyri) typical for normal brain development, multiple small convolutions occur, in the result of which the brain surface appears pebbled. Histologically, polymicrogyria is characterized by a strong reduction (or even the complete lack) of layer V of the cerebral cortex. Further diagnostic criteria include white matter reduction, ventricular enlargement, and hypoplasia of the brainstem and cerebellum (Pabuşçu et al., 2002; Jansen and Andermann, 2005). At least two genes have been found to be associated with polymicrogyria — GPR56 (Piao et al., 2004) and AHI1 gene, though in the latter case, polymicrogyria is only one aspect of a wider disorder, Joubert syndrome (Dixon-Salazar et al., 2004). Polymicrogyria is also frequently associated with deletion 22q11.2 syndrome (Robin et al., 2006), possibly due to perinatal cardiovascular effects (Barkovich et al., 1995).