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Lissencephaly, which literally means smooth brain, is a rare brain formation disorder caused by defective neuronal migration during the 12th to 24th weeks of gestation, resulting in a lack of development of brain folds (gyri) and grooves (sulci).[1] It is a form of cephalic disorder. Terms such as ‘agyria’ (no gyri) or ‘pachygyria’ (broad gyri) are used to describe the appearance of the surface of the brain. Children with lissencephaly are severely neurologically impaired[2] and often die within several months of birth.[3]
Affected children display severe psychomotor retardation, failure to thrive, seizures, and muscle spasticity or hypotonia.[4] Other symptoms of the disorder may include unusual facial appearance, difficulty swallowing, and anomalies of the hands, fingers, or toes.
The diagnosis of lissencephaly is usually made at birth or soon after by ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI). Before birth, complex ultrasounds performed routinely during pregnancy may indicate the presence of cerebral abnormality, but this method of diagnosis is not reliable, and an absence of abnormal cerebral pathology should only inspire cautious optimism at best. In any case, diagnosis by ultrasound probably cannot be reliably made until 26 to 28 weeks, when the normal gyri and sulci become well defined. Up to this time, the fetal brain normally has a smooth appearance.[5] If lissencephaly is suspected, chorionic villus sampling can test for some lissencephaly variants, but only those with a known genetic mutation.
Causes of lissencephaly can include viral infections of the uterus or the fetus during the first trimester, or insufficient blood supply to the fetal brain early in pregnancy. There are also a number of genetic causes of lissencephaly, including mutation of the reelin gene (on chromosome 7),[6] as well as other genes on the X chromosome and on chromosome 17. Genetic counseling is usually offered if there is a risk of lissencephaly, coupled with genetic testing.
The spectrum of lissencephaly is only now becoming more defined as neuroimaging and genetics has provided more insights into migration disorders. There are around 20 different types of lissencephaly which make up the spectrum. Other causes which have not yet been identified are likely as well.
Different systems for classifying lissencephaly exist. One major distinction is “classic” (type I) vs. “cobblestone” (type II),[7] but some systems add additional forms that fit into neither of these categories.
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