Objective: To study cortical excitability, electroencephalography patterns, nerve conduction velocity, and sleep patterns, in succinic semialdehyde dehydrogenase (SSADH) deficiency, a rare autosomal recessive pediatric neurotransmitter disease associated with elevated levels of brain gamma aminobutyric acid (GABA), the major inhibitory neurotransmitter. The clinical phenotype includes mental retardation, epilepsy, and neuropsychiatric manifestations.