| Lissencephaly | |
|---|---|
| Classification and external resources | |
| ICD-10 | Q04.3 |
| ICD-9 | 742.2 |
| DiseasesDB | 29492 |
| MeSH | D054082 |
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]
Contents |
Affected children display severe psychomotor retardation, failure to thrive, seizures, and muscle spasticity or hypotonia.[3] 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,[4] computed tomography (CT), or magnetic resonance imaging (MRI).[5] However, these results should be interpreted cautiously since even experienced radiologists can misdiagnose polymicrogyria, a different developmental malformation of the brain, as lissencephaly.
Before birth, complex ultrasounds performed routinely during pregnancy may indicate the presence of cerebral abnormality, but this method of diagnosis should be complemented by other methods, such as genetic studies and NMR, and the examination is not recommended as part of routine ultrasound examinations, unless family medical history or other reasons for suspecting brain malformation are present. The earliest point during gestation when it is possible to observe abnormal development of the brain surface is approximately in week 20, although ultrasound examinations in week 25-30 is more common.[6] Up to this time, the fetal brain normally has a smooth appearance.[7] 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,[8] 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),[9] 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),[10] 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):
| Category | Types |
| Classic (or Type 1) lissencephaly – 607432 |
|
| Cobblestone (or Type 2) lissencephaly |
|
| Other types |
|
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 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. With modern medications and care, some children live into their teens. Respiratory problems are the most common causes of death.
|
|||||||||||||||||||||||