Cholinergic innervation topography in GBA-associated de novo Parkinson's disease patients

Cholinergic changes in Lewy body disease: implications for presentation, progression and subtypes

Cholinergic degeneration is significant in Lewy body disease, including Parkinson's disease, dementia with Lewy bodies, and isolated REM sleep behaviour disorder. Extensive research has demonstrated cholinergic alterations in the CNS of these disorders. More recently, studies have revealed cholinergic denervation in organs that receive parasympathetic denervation. This enables a comprehensive review of cholinergic changes in Lewy body disease, encompassing both central and peripheral regions, various disease stages and diagnostic categories. Across studies, brain regions affected in Lewy body dementia show equal or greater levels of cholinergic impairment compared to the brain regions affected in Lewy body disease without dementia. This observation suggests a continuum of cholinergic alterations between these disorders. Patients without dementia exhibit relative sparing of limbic regions, whereas occipital and superior temporal regions appear to be affected to a similar extent in patients with and without dementia. This implies that posterior cholinergic cell groups in the basal forebrain are affected in the early stages of Lewy body disorders, while more anterior regions are typically affected later in the disease progression. The topographical changes observed in patients affected by comorbid Alzheimer pathology may reflect a combination of changes seen in pure forms of Lewy body disease and those seen in Alzheimer's disease. This suggests that Alzheimer co-pathology is important to understand cholinergic degeneration in Lewy body disease. Thalamic cholinergic innervation is more affected in Lewy body patients with dementia compared to those without dementia, and this may contribute to the distinct clinical presentations observed in these groups. In patients with Alzheimer's disease, the thalamus is variably affected, suggesting a different sequential involvement of cholinergic cell groups in Alzheimer's disease compared to Lewy body disease. Patients with isolated REM sleep behaviour disorder demonstrate cholinergic denervation in abdominal organs that receive parasympathetic innervation from the dorsal motor nucleus of the vagus, similar to patients who experienced this sleep disorder in their prodrome. This implies that REM sleep behaviour disorder is important for understanding peripheral cholinergic changes in both prodromal and manifest phases of Lewy body disease. In conclusion, cholinergic changes in Lewy body disease carry implications for understanding phenotypes and the influence of Alzheimer co-pathology, delineating subtypes and pathological spreading routes, and for developing tailored treatments targeting the cholinergic system.

Associations of cholinergic system integrity with cognitive decline in GBA1 and LRRK2 mutation carriers

In Parkinson's disease (PD), GBA1- and LRRK2-mutations are associated with different clinical phenotypes which might be related to differential involvement of the cholinergic system. We investigated cholinergic integrity in 149 asymptomatic GBA1 and 169 asymptomatic LRRK2 mutation carriers, 112 LRRK2 and 60 GBA1 carriers with PD, 492 idiopathic PD, and 180 controls from the PPMI cohort. Basal forebrain volumes were extracted and white matter pathways from nucleus basalis of Meynert (NBM) to cortex and from pedunculopontine nucleus (PPN) to thalamus were assessed with a free water-corrected DTI model. Bayesian ANCOVAs were conducted for group comparisons and Bayesian linear mixed models to assess associations with cognitive decline. Basal forebrain volumes were increased in asymptomatic GBA1 (Bayes Factor against the null hypothesis (BF10) = 75.2) and asymptomatic LRRK2 (BF10 = 57.0) compared to controls. Basal forebrain volumes were increased in LRRK2- compared to GBA1-PD (BF10 = 14.5) and idiopathic PD (BF10 = 3.6*107), with no difference between idiopathic PD and PD-GBA1 (BF10 = 0.25). Mean diffusivity along the medial NBM pathway was decreased in asymptomatic GBA1 compared to controls (BF10 = 30.3). Over 5 years, idiopathic PD and PD-GBA1 declined across all cognitive domains whereas PD-LRRK2 patients only declined in processing speed. We found an interaction between basal forebrain volume and time in predicting multiple cognitive domains in idiopathic PD and PD-GBA1, but not in PD-LRRK2. While LRRK2 and GBA1 mutations are both associated with increased basal forebrain volume at asymptomatic stages, this increase persists at the symptomatic PD stage only in LRRK2 and might be related to slower cognitive decline in these patients.

Imaging Biomarkers in Prodromal and Earliest Phases of Parkinson's Disease

Assessing imaging biomarker in the prodromal and early phases of Parkinson's disease (PD) is of great importance to ensure an early and safe diagnosis. In the last decades, imaging modalities advanced and are now able to assess many different aspects of neurodegeneration in PD. MRI sequences can measure iron content or neuromelanin. Apart from SPECT imaging with Ioflupane, more specific PET tracers to assess degeneration of the dopaminergic system are available. Furthermore, metabolic PET patterns can be used to anticipate a phenoconversion from prodromal PD to manifest PD. In this regard, it is worth mentioning that PET imaging of inflammation will gain significance. Molecular imaging of neurotransmitters like serotonin, noradrenaline and acetylcholine shed more light on non-motor symptoms. Outside of the brain, molecular imaging of the heart and gut is used to measure PD-related degeneration of the autonomous nervous system. Moreover, optical coherence tomography can noninvasively detect degeneration of retinal fibers as a potential biomarker in PD. In this review, we describe these state-of-the-art imaging modalities in early and prodromal PD and point out in how far these techniques can and will be used in the future to pave the way towards a biomarker-based staging of PD.