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). 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 generally have significant developmental delays, but these vary greatly from child to child depending on the degree of brain malformation and seizure control. Life expectancy can be shortened, generally due to respiratory problems.
Affected children display severe psychomotor retardation, failure to thrive, seizures, and muscle spasticity orhypotonia. Other symptoms of the disorder may include unusual facial appearance, difficulty swallowing, and anomalies of the hands, fingers, or toes.
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), 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 prognosis for children with lissencephaly varies depending on the malformation. Many individuals remain in a 3-5 month developmental level, while others may appear to have near normal intelligence and development. Some children with lissencephaly will be able to roll over, sit, reach for objects, and smile socially. Aspiration and respiratory disease are the most common causes of illness or death. In the past, life expectancy was said to be around two years of age. However, with advances in seizure control, and treatments for respiratory illness, most children live well beyond that age. With other advances in therapy, and the broader availability of services and equipment, some children with lissencephaly are able to walk with varying degrees of assistance and to perform other functions once thought too advanced.