Change in PDE10 across early Huntington disease assessed by [18F]MNI-659 and PET imaging

Objective: To evaluate whether striatal [F-18]MNI-659 PET imaging of phosphodiesterase 10A (PDE10) serves as a sensitive and reliable biomarker of striatal neurodegeneration in a longitudinal cohort of participants with early Huntington disease (HD). Methods: A cohort of participants with HD, including both participants premanifest or manifest with motor signs, underwent clinical assessments, genetic determination, and 2 [F-18]MNI-659 PET imaging sessions approximately 1 year apart. Eleven healthy control (HC) participants underwent clinical assessments and [F-18]MNI-659 PET imaging once. Striatal binding potentials (BPnd) were estimated for brain regions of interest, specifically within the basal ganglia, and compared between baseline and follow-up imaging. Clinical measures of HD severity were assessed at each visit. Results: Eight participants with HD (6 manifest; 2 premanifest) participated. Of those with manifest HD, all had relatively early stage disease (stage 1, n = 2; stage 2, n = 4) and a Unified Huntington's Disease Rating Scale total motor score <45. As expected, the HD cohort as a whole had a reduction in the basal ganglia BPnd to approximately 50% of that seen in HC. On follow-up scans, [F-18]MNI-659 uptake declined in the putamen and caudate nucleus in all 8 participants. The mean annualized rates of decline in signal in the caudate, putamen, and globus pallidus and the putamen were 16.6%, 6.9%, and 5.8%, respectively. In HC, the annualized reduction in signal in striatal regions was less than 1%. Conclusion: Longitudinal data in this small cohort of participants with early HD support [F-18]MNI-659 PET imaging of PDE10 as a useful biomarker to track HD disease progression.