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Corpus callosum agenesis (CCA) is characterized by total or partial absence of the main interhemispheric commissure, the corpus callosum. CCA is the most common brain malformation with an prevalence of 1-14/2,000. It occurs as an isolated malformation in 49% of cases. Clinical features include intellectual deficit (80%) and/or easily controlled epilepsy and/or behavioural disorders. However, clinical findings vary widely, ranging from asymptomatic cases with normal intellectual capacities to those with severe intellectual deficit. CCA is generally discovered when the child starts school and although febrile seizures appear to be more frequent in CCA patients than in the general population, epilepsy is rare. Behavioural troubles seem to be frequent and may be the first sign of the malformation. The mechanisms leading to CAA remain unknown; however, an anomaly of the commissural plaque (defective migration of the callosal axons or an abnormality of the callosal neurons) has been suggested. Isolated CCA can be sporadic, autosomal recessive or dominant, or X-linked. Although several chromosomes seem to be involved in the development and maintenance of the corpus callosum (1, 8, 13, 15, 18, 21, and X), no gene has yet been identified for isolated CCA. Diagnosis is based on cerebral imaging with transfontanel ultrasonography, magnetic resonance imaging (MRI) and computed tomography (CT). Excluded diseases include CCA associated with: chromosomal abnormalities, a metabolic disease, a viral embryopathy, intoxication (drugs, alcohol) or medication (such as valproate), any brain malformation (posterior fossa abnormalities, gyration defects), or a malformation syndrome (either a defined syndrome such as the Aicardi or orofaciodigital syndromes (see these terms), or an undefined syndrome). Radiological and genetic markers that may enable prediction of asymptomatic or symptomatic disease are not yet available, making genetic counselling difficult when the condition is diagnosed prenatally. Prenatal diagnosis is now routinely made by ultrasonography (20th week) and MRI (30th week). Treatment is symptomatic and consists of physiotherapy, speech therapy, antiepileptic drugs and psychotherapy. Isolated CCA appears to be related to a better prognosis than associated CCA, with up to 80% of isolated CCA cases having a normal outcome. Nevertheless, parents should be informed that learning difficulties (associated with slowness, distractibility and attention deficit) may develop and require appropriate rehabilitation. |