Types of Classical Lissencephaly Seizures

Lissencephaly, which literally means smooth brain, is a birth brain abnormality that results in severe seizures as well as mental retardation. This is caused by the halt in the development of the fetal brain during early pregnancy. There are various types of classical lissencephaly seizures that affect individuals at birth.

Facts

• Classical lissencephaly seizure was first identified in 1914 by Culp and Erhardt, two pathologists who described the condition involving a smooth surface on the human brain, which lacks the normal gyri. Lissencephaly is among a number of conditions that are coined as "neural migration disorders" that occur because the neurons of the brain do not directly go to the cerebral cortex during the critical fetal development. This can be inherited or developed as one of the birth abnormalities.

Type 1 Lissencephaly

• This type is characterized in affected individuals who have a 10 to 20 mm cortex, but no other major brain malformations. This is the only type of lissencephaly that is associated with subcortical band heterotopia. What differs between the two are the pattern and the severity of the abnormality or malformation of the brain. These physical distinctions make diagnosis easier and more important than identifying other syndromes.

Type 2 Lissencephaly

• This second type of classic lissencephaly is also coined as cobblestone dysplasia, pertaining to the appearance that resembles pebbles in the surface of the brain's cortex. The brain of individuals with type 2 lissencephaly often shows malformations of the white matter, abnormally large ventricles, premature brainstem and cerebellum and the lack of corpus callosum. The most common syndromes of the type include cobblestone lissencephaly without the physical birth defects, muscle-eye-brain disease, Walker-Warburg syndrome and the Fukuyama congenital muscular dystrophy.

X-Linked Lissencephaly

• X-linked lissencephaly and the double cortex syndrome are both disorders characterized by the mutations of the DCX or the XLIS gene. The male sex-determined manifestation found in XLIS is characterized by the classic type 1 lissencephaly, mental retardation, as well as severe epilepsy. The mortality rate for this type of condition is high and is often revealed in miscarriages of the male fetus. Meanwhile, the female sex-determined manifestation in the DCX/XLIS gene carries a milder condition of the double cortex syndrome, coming from the appearance seen in MRI scans.

Diagnosis

• Lissencephaly is diagnosed using MRI and CT testing. Type 1 lissencephaly often shows very shallow indentations of the thick cerebral cortex. Another method of diagnosis is clinical evaluation and examination by a medical geneticist, to evaluate a child based on the syndromes. Chromosome testing and other specialized genetic tests are further conducted to finalize and determine the presence of lissencephaly seizures.