GAD1 and cerebellar ataxia: Abs to glutamic acid decarboxylase (GAD), the rate-limiting enzyme in the synthesis of the inhibitory neurotransmitter γ-aminobutyric acid (GABA), have been reported in a number of different neurological syndromes, including stiff person syndrome, cerebellar ataxia, LE, and epilepsy, as well as in individual patients with isolated neurological symptoms.