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NORD is very grateful to Joseph G. Gleeson, MD, Department of Neurosciences, University of California, San Diego, for assistance in the preparation of this report.
Synonyms of Lissencephaly
- lissencephaly, type I
- isolated lissencephaly sequence (ILS)
- lissencephaly 1 (LIS1)
- Miller-Dieker syndrome
- Norman-Roberts syndrome
- subcortical band heterotopia
- x-linked lissencephaly
Classical lissencephaly, also known as lissencephaly type I, is a brain malformation that may occur as an isolated abnormality (isolated lissencephaly sequence [ILS]) or in association with certain underlying syndromes (e.g., Miller-Dieker syndrome, Norman-Roberts syndrome). The condition is characterized by absence (agyria) or incomplete development (pachygyria) of the ridges or convolutions (gyri) of the outer region of the brain (cerebral cortex), causing the brain's surface to appear unusually smooth.
In infants with classical lissencephaly, the head circumference may be smaller than would otherwise be expected (microcephaly). Additional abnormalities may include sudden episodes of uncontrolled electrical activity in the brain (seizures), severe or profound intellectual disability, feeding difficulties, growth retardation, and impaired motor abilities. If an underlying syndrome is present, there may be additional symptoms and physical findings.
Researchers indicate that there may be various possible causes of isolated lissencephaly, including viral infections or insufficient blood flow to the brain during fetal development or certain genetic factors. Changes (mutations) of at least two different genes have been implicated in isolated lissencephaly: a gene located on chromosome 17 (known as LIS1) and a gene located on the X-chromosome (known as XLIS or Doublecortin). There is a third gene known as TUBA1A that has been identified as the 3rd genetic cause for this disorder.
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