A new syndrome of mental retardation and epilepsy characterized by dense microsphere accumulation.

Dense microspheres (DMS) are enigmatic structures found within dendrites in the normal human cortex; their composition and function are unknown. We describe a case of a 29-year-old male with a history of mental retardation and epilepsy in whom the unique neuropathological finding was a marked excess of DMS, most notably in the neocortex. This is a previously undescribed neuropathological syndrome, and represents the first unequivocal association of DMS with a neurological disorder.