Abstract
Two brothers are described with a syndrome characterized by mental retardation, atypical absence, atonic and generalized tonic-clonic seizures, and bilateral symmetrical slow spike and wave discharges on electroencephalograms. Magnetic resonance imaging revealed dysplastic cortex probably representing pachygyria primarily over the parietal regions bilaterally in both patients. The presence of an identical clinical, electroencephalographic, and cortical developmental abnormality on imaging studies in these brothers suggests that a genetic mechanism may play a role in some developmental disorders of the cerebral cortex.