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.