Lissencephaly 1; Lis1

Description

Lissencephaly (LIS), literally meaning smooth brain, is characterized by smooth or nearly smooth cerebral surface and a paucity of gyral and sulcal development, encompassing a spectrum of brain surface malformations ranging from complete agyria to subcortical band heterotopia (SBH). Classic lissencephaly is associated with an abnormally thick cortex, reduced or abnormal lamination, and diffuse neuronal heterotopia. SBH consists of circumferential bands of heterotopic neurons located just beneath the cortex and separated from it by a thin band of white matter. SBH represents the less severe end of the lissencephaly spectrum of malformations (Pilz et al., 1999, summary by Kato and Dobyns, 2003). Agyria, i.e., brain without convolutions or gyri, was considered a rare malformation until recent progress in neuroradiology (Bordarier et al., 1986). With this technical advantage, a number of lissencephaly syndromes have been distinguished.Classic lissencephaly (formerly type I) is a brain malformation caused by abnormal neuronal migration at 9 to 13 weeks' gestation, resulting in a spectrum of agyria, mixed agyria/pachygyria, and pachygyria. It is characterized by an abnormally thick and poorly organized cortex with 4 primitive layers, diffuse neuronal heterotopia, enlarged and dysmorphic ventricles, and often hypoplasia of the corpus callosum. (Lo Nigro et al., 1997).Kato and Dobyns (2003) presented a classification system for neuronal migration disorders based on brain imaging findings and molecular analysis. The authors also reviewed the contributions and interactions of the 5 genes then known to cause human lissencephaly: LIS1 or PAFAH1B1, 14-3-3-epsilon (YWHAE), DCX, RELN, and ARX. Genetic Heterogeneity of LissencephalyLissencephaly is a genetically heterogeneous disorder. See also LIS2 (OMIM ), caused by mutation in the RELN gene (OMIM ) on chromosome 7q22; LIS3 (OMIM ), caused by mutation in the TUBA1A gene (OMIM ) on chromosome 12q13; LIS4 (OMIM ), caused by mutation in the NDE1 gene (OMIM ) on chromosome 16p13; LIS5 (OMIM ), caused by mutation in the LAMB1 gene (OMIM ) on chromosome 7q; LIS6 (OMIM ), caused by mutation in the KATNB1 gene (OMIM ) on chromosome 16q21; LIS7 (OMIM ), caused by mutation in the CDK5 gene (OMIM ) on chromosome 7q36; and LIS8 (OMIM ), caused by mutation in the TMTC3 gene (OMIM ) on chromosome 12q21.X-linked forms include LISX1 (OMIM ), caused by mutation in the DCX gene (OMIM ) on chromosome Xq22.3-q23, and LISX2 (OMIM ), caused by mutation in the ARX gene (OMIM ) on chromosome Xp22.3-p21.1.See also Miller-Dieker lissencephaly syndrome (MDLS ), a contiguous gene microdeletion syndrome involving chromosome 17p13 and including the PAFAH1B1 and YWHAE (OMIM ) genes. Lissencephaly caused by mutations in the PAFAH1B1 gene is also called 'isolated' lissencephaly to distinguish it from the accompanying features of MDLS.

Clinical Features

• Intellectual disability
• Seizures
• Global developmental delay
• Generalized hypotonia
• Microcephaly
• Strabismus
• Abnormal facial shape
• Spasticity
• Ventriculomegaly
• Hypoplasia of the corpus callosum

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