Effects of hyperventilation on fast goal-directed limb movements in spinocerebellar ataxia type 6.

It has been shown previously that hyperventilation modifies the features of the nystagmus in cerebellar patients (Walker and Zee, 1999). It has been hypothesized that hyperventilation influences the oculomotor control through a metabolic effect on cerebellar calcium channels, which play a critical role in the firing behaviour of neuronal populations in the cerebellum. This hypothesis has been tested here by analysing fast goal-directed limb movements before and after hyperventilation in spinocerebellar ataxia type 6 (SCA-6), a disease associated with a polyglutamine expansion in the alpha 1-A voltage-dependent calcium channel. Cerebellar hypermetria associated with fast distal single-joint movements was found to be increased following hyperventilation in patients presenting SCA-6 but remained unchanged in patients with idiopathic late-onset cerebellar degeneration (ILOCA). This is a new provocative test to enhance distal dysmetria in SCA-6. The present results strengthen the hypothesis of Walker and Zee. It is suggested that hyperventilation enhances the defective calcium transfers in SCA-6, resulting in an impairment of the calcium influx in particular into Purkinje cells involved in the control of fast goal-directed voluntary movements.