RAC1 and polymicrogyria: However, the observation that brain size abnormalities are predominant in patients harboring RAC1 variants whereas RAC3 subjects more commonly display malformations of cortical development (polymicrogyria, heterotopia and dysgyria) suggest that RAC1 likely plays a major role in neurogenesis and/or apoptosis, whereas RAC3 is primarily involved in neuronal migration [26,44,92].