Cerebral gyral dysplasias: molecular genetics and cell biology.

The promise of genetics has been partly realized in our understanding of human brain development as this relates to disorders of gyral formation. Cerebral gyral dysplasias are disorders of brain formation that result in phenotypes with the common feature of abnormal cerebral gyri. This review emphasizes the recent progress made in understanding the human lissencephalies and related disorders. LIS1 heterozygous loss-of-function deletions and point mutations, as well as Doublecortin mutations in males, lead to a very similar phenotype, termed type 1 lissencephaly. Additionally, Doublecortin mutations in females lead to a more variable subcortical band heterotopia. Given the similarities between the lissencephaly phenotypes that result from aberrations in these genes, it is important to review the genetics of these disorders. In order to begin to understand the cell biology of the LIS1 protein and the Doublecortin protein, potentially interacting pathways need to be emphasized. Another human genetic disorder with an interestingly similar phenotype has a mouse correlate that has been well characterized. This surprising finding may lead to further understanding of LIS1 protein and of Doublecortin protein. Furthermore, mouse modeling of the aforementioned human disorders now holds promise for enabling us finally to understand the formation of the most complex organ that nature has produced - the human brain.