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  • Updated 12.20.2023
  • Released 10.31.1994
  • Expires For CME 12.20.2026




Lissencephaly is a spectrum of congenital disorders of cortical development wherein cerebral convolutions (gyri) are broad or absent. This spectrum encompasses agyria, pachygyria, and subcortical band heterotopia. Patients suffer from intellectual disability, hypotonia, motor delay, and seizures. There are numerous syndromes that include lissencephaly as a feature. Miller-Dieker syndrome is one of the more common of these and is characterized by facial changes, including tall forehead, thickened upper lip with inverted vermillion border, flattened midface, and a variety of extracranial anomalies. Current MRI classification of lissencephaly encompasses 21 patterns. There is some genotype-phenotype correlation.

Key points

• Lissencephaly is a spectrum congenital disorder of cortical development wherein cerebral convolutions (gyri) are broad or absent.

• Current MRI classification of lissencephaly encompasses 21 patterns (30). There is some genotype-phenotype correlation.

• At present, mutations in recognized genes have been identified in over 80% of patients. This implies that additional genes are yet to be found.

Historical note and terminology

Lissencephaly (literally meaning “smooth brain”) is a neuronal migration disorder that includes both agyria and pachygyria but excludes polymicrogyria and other cortical dysplasias. It was first described in 1904 and was considered rare until CT and MRI scans came into widespread use.

A recognizable "lissencephaly syndrome," later renamed Miller-Dieker syndrome, was described in a series of papers between 1962 and 1980 (89; 33; 62). The association between Miller-Dieker syndrome and visible deletions of chromosome band 17p13.3 was first reported in 1983 (39; 121), and submicroscopic deletions of the same region were reported in 1988 (139). Children with classic lissencephaly who lack the facial changes of Miller-Dieker syndrome are classified separately as isolated lissencephaly sequence (38). The association between isolated lissencephaly sequence and smaller submicroscopic deletions in chromosome 17p13.3 was first described in 1992 (78).

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