18F-FDG PET uptake in the pre-Huntington disease caudate affects the time-to-onset independently of CAG expansion size.

PURPOSE: To test in a longitudinal follow-up study whether basal glucose metabolism in subjects with a genetic risk of Huntington disease (HD) may influence the onset of manifest symptoms. METHODS: The study group comprised 43 presymptomatic (preHD) subjects carrying the HD mutation. They underwent a (18)F-FDG PET scan and were prospectively followed-up for at least 5 years using the unified HD rating scale to detect clinical changes. Multiple regression analysis included subject's age, CAG mutation size and glucose uptake as variables in a model to predict age at onset. RESULTS: Of the 43 preHD subjects who manifested motor symptoms, suggestive of HD, after 5 years from the PET scan, 26 showed a mean brain glucose uptake below the cut-off of 1.0493 in the caudate, significantly lower than the 17 preHD subjects who remained symptom-free (P < 0.0001). This difference was independent of mutation size. Measurement of brain glucose uptake improved the CAG repeat number and age-based model for predicting age at onset by 37 %. CONCLUSION: A reduced level of glucose metabolism in the brain caudate may represent a predisposing factor that contributes to the age at onset of HD in preHD subjects, in addition to the mutation size.