Agenesis of the corpus callosum (ACC) is a birth defect in which the structure that connects the two hemispheres of the brain (the corpus callosum) is partially or completely absent.
Agenesis of the corpus callosum is caused by disruption to development of the fetal brain between the 3rd and 12th week of pregnancy. In most cases, it is not possible to know what caused an individual to have ACC or another callosal disorder. However, research suggests that some possible causes may include chromosome errors, inherited genetic factors, prenatal infections or injuries, prenatal toxic exposures, structural blockage by cysts or other brain abnormalities, and metabolic disorders.
ACC can occur as an isolated condition or in combination with other cerebral abnormalities, including:
- Arnold-Chiari malformation
- Dandy-Walker syndrome
- Andermann syndrome
- Schizencephaly – clefts or deep divisions in brain tissue
- Holoprosencephaly – failure of the forebrain to divide into lobes
Girls may have a gender-specific condition called Aicardi’s syndrome, which causes:
- Severe mental retardation
- Abnormalities in the vertebra of the spine
- Lesions on the retina of the eye
ACC can also be associated with malformations in other parts of the body, such as midline facial defects. The effects of the disorder range from subtle or mild to severe, depending on associated brain abnormalities. Intelligence may be normal with mild compromise of skills requiring matching of visual patterns. But children with the most severe brain malformations may have intellectual retardation, seizures, hydrocephalus, and spasticity.
Prognosis depends on the extent and severity of malformations. ACC does not cause death in the majority of children. Mental retardation does not worsen. Although many children with the disorder have average intelligence and lead normal lives, neuropsychological testing reveals subtle differences in higher cortical function compared to individuals of the same age and education without ACC.
There is no standard course of treatment for ACC. Treatment usually involves management of symptoms and seizures if they occur.