Gray matter heterotopia is a collection of neurological disorders characterized by abnormal migration of progenitor neuronal cells resulting in clusters or bands of neurons usually distributed along the periventricular region to the overlying cortical mantle. These abnormal collections of neurons can occur anywhere from the subependyma to the cortical mantle, with the location determining the disorder and the phenotype. The commonly affected regions include the subependyma with nodular, solitary heterotopia and bands in the subcortical region leading to subcortical band heterotopia syndromes. They are generally proportionate in size relative to brain volume. When these clusters or bands of gray matter neurons grow at a disproportionate rate relative to brain growth, it is concerning for slow-growing malignancies such as oligodendrogliomas and dysembryoplastic neuroepithelial tumors. The neurogenetics of heterotopic syndromes is a rapidly...