Agenesis of corpus callosum (ACC) is a rare disorder that is present at birth (congenital). It is characterized by a partial or complete absence (agenesis) of an area of the brain that connects the two cerebral hemispheres. This part of the brain is normally composed of transverse fibers. The cause of agenesis of corpus callosum is usually not known, but it can be inherited as either an autosomal recessive trait or an X-linked dominant trait. It can also be caused by an infection or injury during the twelfth to the twenty-second week of pregnancy (intrauterine) leading to developmental disturbance of the fetal brain. Intrauterine exposure to alcohol (Fetal alcohol syndrome) can also result in ACC. In some cases mental retardation may result, but intelligence may be only mildly impaired and subtle psychosocial symptoms may be present.
ACC is frequently diagnosed during the first two years of life. An epileptic seizure can be the first symptom indicating that a child should be tested for a brain dysfunction. The disorder can also be without apparent symptoms in the mildest cases for many years.