TSPO and Huntington disease: A meta-analysis with first and second generation of TSPO tracers shows that TSPO PET signal in cortical grey matter increases in patients with AD (standardized mean difference [SMD] = 0.693, P < 0.001) and other NDDs including ALS, PD, FTD, DLB and HD (SMD = 0.929, P < 0.001) compared to controls.