Lissencephaly

A brain malformation characterized by microcephaly and the lack of normal convolutions (folds) in the brain. Lissencephaly literally means "smooth brain." It is caused by defective neuronal migration, a defect in the process in which nerve cells move from their place of origin to their permanent location. The surface of a normal brain is formed by a complex series of folds and grooves. The folds are called gyri or convolutions, and the grooves are called sulci. In children with lissencephaly, the normal convolutions are absent or only partly formed, making the surface of the brain smooth. Children born with lissencephaly may have an unusual facial appearance, difficulty swallowing, failure to thrive, and severe psychomotor retardation. Anomalies of the hands, fingers, or toes, muscle spasms, and seizures may also occur. Lissencephaly may be diagnosed at or soon after birth. Diagnosis may be confirmed by ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI). There are several distinct genetic causes of lissencephaly. Genes known to be involved in causing lissencephaly have been mapped to at least 4 autosomes (chromosomes 2, 7, 9 and 17) and 17p13.3 and the X chromosome. The spectrum of lissencephaly is only now becoming more defined as neuroimaging and genetics has provided more insights into migration disorders. Other causes which have not yet been identified are likely as well. Lissencephaly can be associated with other diseases including isolated lissencephaly sequence, the Miller-Dieker syndrome (in chromosome band 17p13.3), and the Walker-Warburg syndrome (in chromosome band 9q31). Treatment for those with lissencephaly is symptomatic and depends on the severity and locations of the brain malformations. Supportive care may be needed to help with comfort and nursing needs. Seizures may be controlled with medication and hydrocephalus may require shunting. If feeding becomes difficult, a gastrostomy tube may be considered. The prognosis (outlook) for children with lissencephaly varies depending on the degree of brain malformation. Many individuals show no significant development beyond a 3- to 5-month-old level. Some may have near-normal development and intelligence. Many will die before the age of 2. Respiratory problems are the most common causes of death.

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SYN: agyria. [G. lissos, smooth, + enkephalos, brain]

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lis·sen·ceph·a·ly .lis-en-'sef-ə-lē n, pl -lies the condition of having a smooth cerebrum without convolutions

lis·sen·ce·phal·ic -sə-'fal-ik adj

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(smooth brain)

n.

a condition in which the brain develops abnormally - it has no grooves on the outside, large ventricles, and generally is smaller than it should be. Lissencephaly causes severe mental retardation and failure to thrive. See also Miller-Deiker syndrome.

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lis·sen·ceph·a·ly (lis″ən-sefґə-le) agyria.