Moreover, prolonged proliferation of cortical progenitor cells could not only underlie the macrocephaly in acrocallosal syndrome patients who carry mutations in GLI3, but also the agenesis of the corpus callosum in these patients (Bonatz et al., 1997; Elson et al., 2002; Philip et al., 1988; Schinzel, 1979). The gene discussed is GLI3; the disease is acrocallosal syndrome.