An altered GABA-A receptor function in spinocerebellar ataxia type 6 and familial hemiplegic migraine type 1 associated with the CACNA1A gene mutation

BACKGROUND: Mutations in the CACNA1A gene encoding the voltage-gated calcium channel α1A subunit have been identified in patients with autosomal dominantly inherited neurological disorders, including spinocerebellar ataxia type 6 (SCA6) and familial hemiplegic migraine type 1 (FHM1). In order to investigate the underlying pathogenesis common to these distinct phenotypic disorders, this study investigated the neuronal function of the GABAergic system and glucose metabolism in vivo using positron emission tomography (PET). METHODS: Combined PET studies with [(11)C]-flumazenil and [(18)F]-fluorodeoxyglucose (FDG) were performed in three FHM1 patients and two SCA6 patients. [(18)F]-FDG-PET using a three-dimensional stereotactic surface projection analysis was employed to measure the cerebral metabolic rate of glucose (CMRGlc). In addition, the GABA-A receptor function was investigated using flumazenil, a selective GABA-A receptor ligand. RESULTS: All patients displayed a significant decrease in CMRGlc and low flumazenil binding in the cerebellum compared with the normal controls. The flumazenil binding in the temporal cortex was also decreased in two FHM1 patients. CONCLUSIONS: Cerebellar glucose hypometabolism and an altered GABA-A receptor function are characteristic of FHM1 and SCA6. GENERAL SIGNIFICANCE: An altered GABA-A receptor function has previously been reported in models of inherited murine cerebellar ataxia caused by a mutation in the CACNA1A gene. This study showed novel clinical characteristics of alteration in the GABA-A receptor in vivo, which may provide clinical evidence indicating a pathological mechanism common to neurological disorders associated with CACNA1A gene mutation.