α-synuclein RT-QuIC in cerebrospinal fluid of LRRK2 linked Parkinson’s disease

Background: leucine-rich kinase 2 (LRRK2)-linked Parkinson's disease (PD) is clinically indistinguishable from idiopathic PD (IPD). A pleiotropic neuropathology has been recognized but the majority of studies in LRRK2 p.G2019S patients reveal Lewy-type synucleinopathy as its principal histological substrate. To date no in vivo biomarkers of synucleinopathy have been found in LRRK2 mutation carriers. Objectives: we used real-time quaking-induced conversion (RT-QuIC) technique to assess the presence of alpha-synuclein (a-syn) aggregates in cerebrospinal fluid (CSF) of LRRK2 p.G2019S carriers. Methods: CSF samples of 51 subjects were analyzed: 15 LRRK2 p.G2019S PD, 10 IPD, 16 LRRK2 p.G2019S nonmanifesting carriers (NMC) and 10 healthy controls. The presence of parkinsonism and prodromal symptoms was assessed in all study subjects. Results: forty percent (n = 6) LRRK2-PD, and 18.8% (n = 3) LRRK2-NMC had a positive a-syn RT-QuIC response. RT-QuIC detected IPD with 90% sensitivity and 80% specificity. No clinical differences were detected between LRRK2-PD patients with positive and negative RT-QuIC. A positive RT-QuIC result in LRRK2-NMC occurred in a higher proportion of subjects meeting the Movement Disorder Society research criteria for prodromal PD. Interpretation: RT-QuIC detects a-syn aggregation in CSF in a significant number of patients with LRRK2-PD, but less frequently than in IPD. A small percentage of LRRK2-NMC tested also positive. If appropriately validated in long-term studies with large number of mutation carriers, and hopefully, postmortem or in vivo confirmation of histopathology, RT-QuIC could contribute to the selection of candidates to receive disease modifying drugs, in particular treatments targeting a-syn deposition

Nigral and striatal connectivity alterations in asymptomatic LRRK2 mutation carriers: A magnetic resonance imaging study

Background. The study of the functional connectivity by means of magnetic resonance imaging (MRI) in asymptomatic LRRK2 mutation carriers could contribute to the characterization of the prediagnostic phase of LRRK2 associated Parkinson's disease (PD). Objective. To characterize MRI functional patterns during resting state in asymptomatic LRRK2 mutation carriers. Methods. We acquired structural and functional MRI data of 18 asymptomatic LRRK2 mutation carriers and 18 asymptomatic LRRK2 mutation noncarriers, all first-degree relatives of LRRK2-PD patients. Starting from resting state data, we analyzed the functional connectivity of the striatocortical and the nigrocortical circuitry. Structural brain data was analyzed by voxel based morphometry, cortical thickness and volumetric measures. Results: Asymptomatic LRRK2 mutation carriers had functional connectivity reductions between the caudal motor part of the left striatum and ipsilateral precuneus and superior parietal lobe. Connectivity in these regions correlated with subcortical gray matter volumes in mutation carriers. Asymptomatic carriers also showed increased connectivity between the right substantia nigra and bilateral occipital cortical regions (occipital pole and cuneus bilaterally, and right lateral occipital cortex). No intergroup differences in structural MRI measures were found. In LRRK2 mutation carriers, age and functional connectivity correlated negatively with striatal volumes. Additional analyses including only subjects with the G2019S mutation revealed similar findings. Conclusion: Asymptomatic LRRK2 mutation carriers showed functional connectivity changes in striatocortical and nigrocortical circuits compared with noncarriers. These findings support the concept that altered brain connectivity precedes the onset of classical motor features in a genetic form of PD