downbeat nystagmus

The cause of downbeat nystagmus (DBN) remains undiag-nosed in about 40 % of patients. This paper reports the presence of antiglutamic acid decarboxylase antibodies (GAD-Ab) in a patient with DBN. Antibodies against GABAergic neurons located in the vestibular complex may induce chemical denervation of the floccular neurons, which normally suppress the peripheral imbalance between vertical semicircular canal systems, thereby caus-ing DBN. Testing for GAD-Ab may be indicated in DBN patients without an identifiable anatomical brain lesion. Downbeat nystagmus (DBN) is defined as a spontaneousnystagmus present with fixation in the primary positionor on lateral gaze, characterised by downward fast phases. A proportion of patients with DBN have an identifiable anatomical lesion of the vestibulocerebellum and underlying medulla. However, the cause of DBN remains undiagnosed in about 40 % of patients, in whom nystagmus is considere