PDE10A and Huntington disease: One concern is that early death of striatal neurons might deplete PDE10A levels to the extent that the target is lost; however, PET imaging with the PDE10A radioligand [18F]-MNI-695 suggests that enzyme levels are sufficient even in manifest HD to expect a meaningful response.71 Clinical trials of PDE10A inhibition in HD patients are already underway, with motor and functional MRI endpoints.72 Other phosphodiesterases implicated in HD pathogenesis are also under study.