<unk>  <unk>  is a rare birth defect (congenital disorder) in which there is a complete or partial absence of the<unk><unk> .<unk>  occurs when the<unk><unk> , the band of tissue connecting the two hemispheres of the brain, fails to develop normally, typically in utero, resulting in disconnected brain hemispheres. The development of the fibers which would otherwise form the<unk><unk>  become longitudinally orientated within each hemisphere and form structures called Probst Bundles.
In addition to<unk> , other callosal disorders include hypogenesis (partial formation), dysgenesis (malformation) of the<unk><unk> , and hypoplasia (underdevelopment) of the<unk><unk> . 
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.
Agenesis of the corpus callosum
Germinal matrix hemorrhage
Cerebellar hypoplasia
Pontocerebellar hypoplasia
Corticobasal degeneration
Incontinentia pigmenti achromians
Leukoencephalopathy with vanishing white matter
X-linked intellectual disability