Agenesis of corpus callosum (HP_0001274) is absence of the corpus callosum as a result of the failure of the corpus callosum to develop, which can be the result of a failure in any one of the multiple steps of callosal development including cellular proliferation and migration, axonal growth or glial patterning at the midline. Also known as: Absence of corpus callosum, Absent corpus callosum, Agenesis of the corpus callosum, Callosal agenesis, Corpus callosum agenesis, Dysplastic or absent corpus callosum.