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What is Agenesis of the corpus callosum and explain in detail?
Agenesis of the corpus callosum (ACC) is a rare birth defect in which there is a complete or partial absence of the corpus callosum. It occurs when the development of the corpus callosum, the band of white matter connecting the two hemispheres in the brain, in the embryo is disrupted. The result of this is that the fibers that would otherwise form the corpus callosum are instead longitudinally oriented along the ipsilateral ventricular wall and form structures called Probst bundles.
In addition to agenesis, other degrees of callosal defects exist, including hypoplasia (underdevelopment or thinness), hypogenesis (partial agenesis) or dysgenesis (malformation).ACC is found in many syndromes and can often present alongside hypoplasia of the cerebellar vermis. When this is the case, there can also be an enlarged fourth ventricle or hydrocephalus; this is called Dandy–Walker malformation.

Signs and symptoms
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, delayed toilet training and dysautonomic symptoms such as low perception of pain or 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 often resembles that of 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 intellectual disability.

Associated brain anomalies
Brain anomalies that can sometimes occur in syndromes that cause callosal disorders include:
Aplasia of the cerebellar vermis
Chiari malformation
Colpocephaly
Dandy–Walker syndrome
Holoprosencephaly
Hydrocephalus
Neuronal migration disorders such as grey matter heterotopia
Schizencephaly

Associated syndromes and conditions
Some syndromes that frequently include ACC are:
Acrocallosal syndrome
Aicardi syndrome
Andermann syndrome
Donnai–Barrow syndrome
Dwarfism
FG syndrome
L1CAM syndrome
Microcephalic osteodysplastic primordial dwarfism type II
Mowat–Wilson syndrome
Oculocerebrocutaneous syndrome
Saal Bulas syndrome
Septo-optic dysplasia (optic nerve hypoplasia)
Shapiro syndrome
Vici syndromeSome conditions that can sometimes be associated with ACC or other callosal disorders include:
1p36 deletion syndrome
13q deletion syndrome
CDK13-related disorder
Craniofacial abnormalities and other oral and maxillofacial pathologies
Fetal alcohol syndrome
Fetal warfarin syndrome
Genitopatellar syndrome
Gomez-Lopez-Hernandez syndrome
Joubert syndrome
Lujan–Fryns syndrome
Marden–Walker syndrome
Maternal nutritional deficiencies or infections
Metabolic disorders
Okamoto syndrome
Opitz G/BBB syndrome
Pascual-Castroviejo syndrome
Pitt–Hopkins syndrome
Sensenbrenner syndrome
Strømme syndrome
Triploid syndrome
Trisomy 9
Xia-Gibbs syndrome

Causes
Agenesis of the corpus callosum is caused by disruption to development of the fetal brain between the 3rd and 12th weeks 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.

Ciliopathies: rare genetic disorders
Until recently, the medical literature did not indicate a connection among many genetic disorders, both genetic syndromes and genetic diseases, that are now being found to be related