γ-Aminobutyric acid (GABA)-transaminase deficiency is an ultra-rare disorder of GABA metabolism that was described for decades as an early-onset epileptic encephalopathy plus movement disorder and hypersomnolence with mortality in early childhood. We report 2 affected siblings in adolescence and adulthood, both with profound developmental impairment, intractable epilepsy, movement disorder, and behavioral fluctuations. This considerably expands the phenotype and longevity of this inherited neurotransmitter disease.
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