Otolith-ocular responses in familial episodic ataxia linked to chromosome 19p

We evaluated several members of a family with episodic ataxia type 2 linked to chromosome 19p by using a battery of vestibulo-ocular reflex (VOR) tests. Testing focused on the otolith-ocular reflex and semicircular canal-otolith interaction. Our aims were to improve understanding of the structures important for the VOR and to define further the range of vestibulo-ocular, in particular otolith-ocular, manifestations within a family with episodic ataxia. Ocular motor, semicircular canal-ocular, and semicircular canal-otolith interaction assessments suggested impairment of the vestibulo-cerebellum (ie, the flocculonodular lobe); the brainstem appeared to be relatively spared. Eye movements during constant velocity off-vertical axis rotation (OVAR), a pure otolith stimulus, indicated that the modulation component of the response was normal whereas the bias component was reduced or nearly absent. Based on these data, it appears that the cerebellum is not responsible for the generation of the modulation component of the response to OVAR. However, the bias component appears to depend on the caudal midline cerebellum.