Lissencephaly (, meaning "smooth brain") is a set of rare brain disorders whereby the whole or parts of the surface of the brain appear smooth. It is 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) and 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. Symptoms and signs
Affected children display severe psychomotor impairment, failure to thrive, seizures, and muscle spasticity or hypotonia. Other symptoms of the disorder may include unusual facial appearance, difficulty swallowing, and anomalies of the hands, fingers, or toes. Symptoms of lissencephaly are detected via ultrasound at about twenty-three weeks and require confirmation from a prenatal MRI. It is characterised by absence or reduction of the sulci and gyri of the cerebral surface and a thickened cortex.There are anatomical symptoms that differ across the two main types of lissencephaly, Classical (Type I) and Cobble Stone (Type 2). In Classical lissencephaly the cortex becomes thickened and can be identified by four layers of the cerebral cortex rather than six.Cobblestone lissencephaly is named after the pebbled or cobblestone appearance of the cortical surface.
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), but some systems add additional forms that fit into neither of these categories. Some types of lissencephaly are described below (OMIM numbers are included where available):

Treatment
Treatment for those with lissencephaly is symptomatic and depends on the severity and locations of the brain malformations. Treatment is tailored towards the symptoms of the individual. Therapies for lissencephaly are to deal with the symptoms as the syndrome is congenital. 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. There are a number of organisations that raise awareness and funding for rare disabilities such as lissencephaly. They also seek to increase the quality of life for individuals living with related disabilities. In the United States, these organizations include Arc of the United States, National Organization for Rare Disorders, and March of Dimes. Prognosis
The prognosis for children with lissencephaly varies depending on the malformation and severity of the syndrome. Many individuals remain at a 3–5 month developmental level. Life expectancy is short and many children with lissencephaly will die before the age of 10. 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.