CACNA1A mutations causing episodic and progressive ataxia alter channel trafficking and kinetics

Background: CACNA1A encodes Ca(V)2.1, the pore-forming subunit of P/Q-type voltage-gated calcium channel complexes. Mutations in CACNA1A cause a wide range of neurologic disturbances variably associated with cerebellar degeneration. Functional studies to date focus on electrophysiologic defects that do not adequately explain the phenotypic findings. Objective: To investigate whether some missense mutations might interfere with protein folding and trafficking, eventually leading to protein aggregation and neuronal injury. Methods: The authors studied the functional consequences of two pore missense mutations, C287Y and G293R, in two families with EA2, one newly discovered and the other previously reported. Both mutations caused episodic and interictal ataxia. The biophysical properties of mutant and wild type calcium channels were examined by whole-cell patch-clamp recordings in transfected COS-7 cells. The plasma membrane targeting was visualized by confocal fluorescence imaging on CaV2.1 tagged with green fluorescent protein. Results: The mutant channels exhibited a marked reduction in current expression and deficiencies in plasma membrane targeting. Conclusions: In addition to altered channel function, the deficiency in protein misfolding and trafficking associated with the C287Y and G293R mutants may contribute to the slowly progressive cerebellar ataxia.