<P> Agenesis of the corpus callosum (ACC) is a rare birth defect (congenital disorder) in which there is a complete or partial absence of the corpus callosum . It occurs when the corpus callosum, the band of white matter connecting the two hemispheres in the brain, fails to develop normally, typically during pregnancy . The fibers that would otherwise form the corpus callosum become longitudinally oriented along the ipsilateral ventricular wall and form structures called Probst bundles . </P> <P> In addition to agenesis of the corpus callosum, other callosal disorders include hypogenesis (partial agenesis, usually referring to the length), dysgenesis (malformation) and hypoplasia (underdevelopment, usually referring to the thickness) of the corpus callosum . </P> <P> Signs and symptoms of ACC and other callosal disorders vary greatly among individuals . However, some characteristics common in individuals with callosal disorders include vision impairments, low muscle tone (hypotonia), poor motor coordination, delays in motor milestones such as sitting and walking, low perception of pain, delayed toilet training, and chewing and swallowing difficulties . Laboratory research has demonstrated that individuals with ACC have difficulty transferring more complex information from one hemisphere to the other . They also have been shown to have some cognitive disabilities (difficulty in complex problem solving) and social difficulties (missing subtle social cues), even when their intelligence quotient is normal . Recent research suggests that specific social difficulties may be a result of impaired face processing . The unusual social behavior in childhood is often mistaken for or misdiagnosed as an autism spectrum disorder . Other characteristics sometimes associated with callosal disorders include seizures, spasticity, early feeding difficulties and / or gastric reflux, hearing impairments, abnormal head and facial features, and a mental handicap . </P> <P> Some syndromes that frequently include ACC are Aicardi syndrome, Andermann syndrome, Shapiro syndrome, acrocallosal syndrome, septo - optic dysplasia (optic nerve hypoplasia), Mowat--Wilson syndrome, John Sayden syndrome, Menkes syndrome, and L1CAM Syndrome . Some conditions that are sometimes associated with ACC include maternal nutritional deficiencies or infections, metabolic disorders, fetal alcohol syndrome, craniofacial abnormalities, and other oral and maxillofacial pathologies . </P>

A child born with agenesis of the corpus callosum would have the most difficulty