Relationship between type 1 metabotropic glutamate receptors and cerebellar ataxia.

Imaging of type 1 metabotropic glutamate receptor (mGluR1) has recently become possible using positron emission tomography (PET). We aimed to examine the relationship between mGluR1 and cerebellar ataxia. Families with spinocerebellar ataxia type 19/22 (SCA19/22) and SCA6, six patients with sporadic SCA, and 26 healthy subjects underwent PET using an mGluR1 radiotracer. Volumes-of-interest were placed on the anterior and posterior lobes and vermis. The binding potential (BPND) was calculated to estimate mGluR1 availability. A partial volume correction was applied to the BPND values. The Scale for the Assessment and Rating of Ataxia (SARA) score were measured. In each patient with SCA19/22 and SCA6, the anterior lobe showed the highest decrease rates in the BPND values, compared with healthy subjects. In the families with SCA19/22 and SCA6, the disease durations and SARA scores were shorter and lower, respectively, in the offspring, compared with the parents. However, the offspring paradoxically showed lower BPND values, especially in the anterior lobe, compared with the parents. The patients with sporadic SCA showed significantly lower BPND values in all subregions than healthy subjects. The BPND values significantly correlated with the SARA scores in all participants. In conclusion, these results showed a decrease in mGluR1 availability in patients with hereditary and sporadic SCA, a correlation between mGluR1 availability and degree of cerebellar ataxia, and paradoxical findings in two families. These results suggest the potential use of mGluR1 imaging as a specific biomarker of cerebellar ataxia.