Aicardi syndrome is a rare genetic disorder affecting females only (ie it is X-linked). There is a partial or complete absence of the corpus callosum, the part of the brain which sits between the right and left sides of the brain and allows the right side to communicate with the left. Characteristics and symptoms of the syndrome are infantile spasms, mental retardation, lesions or "lacunae" of the retina of the eye that are very specific to this disorder, and sometimes other types of defects of the brain such as microcephaly (small brain; enlarged ventricles) or proencephalic cysts (a gap in the brain where there should be healthy brain tissue).
The number of identified cases of girls with Aicardi syndrome is approximately 300-500 worldwide.