Agenesis of the corpus callosum is a condition in which the pathway that connects the two sides of the brain, known as the corpus callosum, does not form, resulting in the complete separation of the two sides of the brain.
Since a normal corpus callosum forms by the seventeenth week of pregnancy, agenesis of the corpus callosum is typically not diagnosed until the late second or third trimesters. To confirm the diagnosis, magnetic resonance imagining (MRI) and/or 3D ultrasounds may be performed. Agenesis of the corpus callosum occurs in less than 1% of the general population, but the diagnosis has an estimated incidence rate of 2-3% among developmentally disabled people.
Agenesis of the corpus callosum can occur as an isolated condition, and on its own, the condition is not a fatal diagnosis. However, due to the high incidence of associated abnormalities, a full anatomy scan and prenatal genetic testing should be conducted. Agenesis of the corpus callosum has been associated with aneuploidy such as trisomy 13 and trisomy 18, central nervous system conditions such as Chiari malformation, encephalocele, holoprosencephaly, and malformations of the face, organ systems and skeleton.
The recurrence risk depends on the underlying cause. When associated with chromosomal abnormalities, the recurrence risk is 1% or the maternal age-related risk, whichever is greater. For isolated cases where the underlying cause is unknown, the recurrence risk is 2-3%.