18F-FDG PET findings in Parkinson's disease associated to RAB32 S71R variant

Objective: The RAB32 S71R variant has been linked to autosomal dominant Parkinson's disease (RAB32-PD), sharing common biological mechanisms with the leucine-rich repeat kinase-2 (LRRK2) gene. Measurement of regional differences in glucose metabolism with 18F-fluorodeoxyglucose (FDG) PET may improve the understanding of the neural mechanisms of RAB32-related PD and non-mutated PD (NM-PD). In this brief communication, we compared FDG-PET findings of eight RAB32-PD with a cohort of NM-PD. Methods: Brain FDG-PET study was performed during the ON medication condition under chronic dopaminergic treatment. All images were normalized to a standard FDG-PET template, then a semi-quantitative analysis was performed on a commercially available fully-automated post-processing software (Cortex ID SUITE, GE Healthcare). Clinical assessment included the MDS-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and the Montreal Cognitive Assessment (MoCA). Continuous variables between groups were compared through the Mann-Whitney test while nominal/ordinal variables through the chi-squared test. Results: Eight RAB32-PD patients (males:3/8; age:65.38 years [±8.73]; disease duration:10.50 years [±5.88]; H&Y:2.81[±1.22]; MDS-UPDRS-III:36.38 [±25.34]; MoCA:24.88[±5.86]) and 19 NM-PD patients (males:11/19; age:60.53 years [±8.00]; disease duration:8.68 years [±5.70]; H&Y:2.39 [±.51]; MDS-UPDRS-III:29.95 [±11.14]; MoCA:24.21 [±6.07]) were included. No statistically significant differences in FDG-PET data and clinical variables were found between RAB32-PD and NM-PD cohorts. In the majority of RAB-32 PD patients a prevalent parietal hypometabolism was observed, similar to previous findings reported in LRRK2-related PD and NM-PD. Interpretation: This study represents the first description of FDG-PET findings in RAB32-PD patients, highlighting a possible similar pattern of hypometabolism with LRRK2- and NM-PD. Additional studies with matched and comparable control cohorts are needed to confirm these preliminary results.