Characterization of the dominant inheritance mechanism of Episodic Ataxia type 2.

Episodic Ataxia type 2 (EA2) is an autosomal dominant neuronal disorder linked to mutations in the Ca2.1 subunit of P/Q-type calcium channels. In vitro studies have established that EA2 mutations induce loss of channel activity and that EA2 mutants can exert a dominant negative effect, suppressing normal Ca2.1 activity through protein misfolding and trafficking defects. To date, the role of this mechanism in the disease pathogenesis is unknown because no animal model exists. To address this issue, we have generated a mouse bearing the R1497X nonsense mutation in Ca2.1 (Ca2.1). Phenotypic analysis of heterozygous Ca2.1 mice revealed ataxia associated with muscle weakness and generalized absence epilepsy. Electrophysiological studies of the cerebellar circuits in heterozygous Ca2.1 mice highlighted severe dysregulations in synaptic transmission of the two major excitatory inputs as well as alteration of the spontaneous activity of Purkinje cells. Moreover, these neuronal dysfunctions were associated with a strong suppression of Ca2.1 channel expression in the cerebellum of heterozygous Ca2.1 mice. Finally, the presence of Ca2.1 in cerebellar lipid raft microdomains was strongly impaired in heterozygous Ca2.1 mice. Altogether, these results reveal a pathogenic mechanism for EA2 based on a dominant negative activity of mutant channels.