Lanau-Kleffner syndrome (LKS), also called infantile acquired aphasia, acquired epileptic aphasia or aphasia with convulsive disorder, is a rare, childhood neurological syndrome characterized by the sudden or gradual development of aphasia (the inability to understand or express language) and an abnormal electroencephalogram (EEG). LKS affects the parts of the brain that control comprehension and speech. The disorder usually occurs in children between the ages of 5 and 7 years. Typically, children with LKS develop normally but then lose their language skills. While many of the affected individuals have clinical seizures, some only have electrographic seizures, including electrographic status epilepticus of sleep (ESES).