Downbeat Nystagmus and Convergence Spasm in a Patient with GAD Autoimmunity Syndrome

Glutamic acid decarboxylase (GAD) enzymatically catalyses decarboxylation of glutamate to gamma-amino butyric acic (GABA), the major inhibitory CNS neurotransmitter. High levels of autoantibodies to GAD are associated with numerous neurologic disorders including stiffman syndrome, limbic encephalitis, epilepsy,and cerebellar ataxia. Many patients have comorbid type I diabetes