The field of neurodegenerative diseases is a major challenge faced by public health and is still in need of robust preventive measures and disease-modifying treatments. Population-based studies can offer the framework in the context of primary and secondary prevention of neurodegenerative diseases. The epidemiology of neurodegenerative disorders in the last decades has focused on descriptive studies mainly based on the use of clinical criteria. However, clinical definition is basically insufficient both to well-characterize different phenotypes and to make an early diagnosis. Descriptive epidemiology needs a new framework to update the area of neurodegenerative research, based on the advancement of both clinical and biological diagnostic criteria and the urgency for an early diagnosis of the disease. In here, we address the present and future of population-based studies in neurodegenerative disorders and discuss the shift of paradigms in the diagnosis of disease and disease definition. We further debate the changes in biomarker implementation models and type of biomarkers used in population-based studies. Descriptive epidemiology of neurodegenerative disorders is rapidly evolving. These implementations will improve the future design and outcome of population-based studies and policy-making in public health intervention.

Background: Constipation is regarded as one of the prodromal features of Parkinson’s disease (PD) and there is emerging evidence linking gastrointestinal dysfunction and cognitive impairment (CI) in PD. Objective: We explored whether constipation is associated with development of CI in two independent cohorts of de novo PD patients (n = 196 from the Non-motor International Longitudinal Study [NILS] and n = 423 from the Parkinson’s Progression Markers Initiative [PPMI] study). Methods: Constipation was clinically defined using the Non-Motor Symptoms Scale (NMSS) item-21 [NILS] and Scales for Outcomes in PD-Autonomic (SCOPA-AUT) item-5 [PPMI]. We assessed baseline group differences (PD with or without constipation) in CI, global non-motor symptoms burden, motor dysfunction, and striatal dopaminergic denervation. Kaplan-Meier method estimated group differences in cumulative proportion of patients with incident CI over three years. In PPMI, we subsequently performed univariate and multivariate Cox survival analyses to evaluate whether constipation predicts incident mild cognitive impairment or dementia over a 6-year period, including constipation and other known predictors of CI as covariates. Results: Patients with constipation had greater motor and global non-motor burden in both cohorts at baseline (p < 0.05). Kaplan-Meier plots showed faster conversion to CI in patients with constipation in both cohorts (p < 0.05). In PPMI, 37 subjects developed dementia during a mean follow-up of 4.9 years, and constipation was an independent predictor of dementia onset (hazard ratio = 2.311; p = 0.02). Conclusion: Constipation in de novo PD patients is associated with development of cognitive decline and may serve as a clinical biomarker for identification of patients at risk for cognitive impairment.

To date, there are no clinically effective neuroprotective or disease-modifying treatments that can halt Parkinson's disease (PD) progression. The current clinical approach focuses on symptomatic management. This failure may relate to the complex neurobiology underpinning the development of PD and the absence of true translational animal models. In addition, clinical diagnosis of PD relies on presentation of motor symptoms which occur when the neuropathology is already established. These multiple factors could contribute to the unsuccessful development of neuroprotective treatments for PD. Prodromal symptoms develop years prior to formal diagnosis and may provide an excellent tool for early diagnosis and better trial design. Patients with idiopathic rapid eye movement behavior disorder (iRBD) have the highest risk of developing PD and could represent an excellent group to include in neuroprotective trials for PD. In addition, repurposing drugs with excellent safety profiles is an appealing strategy to accelerate drug discovery. The anti-diabetic drug metformin has been shown to target diverse cellular pathways implicated in PD progression. Multiple studies have, additionally, observed the benefits of metformin to counteract other age-related diseases. The purpose of this viewpoint is to discuss metformin's neuroprotective potential by outlining relevant mechanisms of action and the selection of iRBD patients for future clinical trials in PD.

Importance: Comprehensive incidence and prevalence rates of frontotemporal dementia are currently not available. Objective: To estimate the incidence and prevalence of frontotemporal dementia and its clinical variants in the overall population and age subgroups. Data Sources and Study Selection: We systematically searched PubMed, EMBASE, and Scopus between January 1, 1990, and October 22, 2024, for population-based studies estimating the incidence and/or prevalence of FTD. Data Extraction and Synthesis: Studies and data were screened and extracted independently by 2 investigators in accordance with PRISMA guidelines. Incident and prevalent cases together with the population at risk were pooled using random-effects meta-analysis. Differences in heterogeneity by FTD variants and populations at risk were estimated. Main Outcomes and Measures: Prevalent and incident cases as numerator were based on well-defined clinical criteria. Denominators were derived either from census population data or from author-defined populations at risk. Results: From 1854 screened articles, 32 eligible population-based studies were identified. Sixteen were on prevalence and 22 on incidence reporting FTD measures, including those with estimates for the whole population and for specific age subgroups. Pooled crude incidence for FTD was 2.28 (95% CI, 1.55-3.36) per 100 000 person-years and prevalence, 9.17 (95% CI, 3.59-23.42) per 100 000 people. The behavioral-variant FTD pooled crude incidence was 1.20 (95% CI, 0.67-2.16) per 100 000 person-years and prevalence, 9.74 (95% CI, 2.90-32.73) per 100 000 people. The primary progressive aphasia variant pooled crude incidence was 0.52 (95% CI, 0.35-0.79) per 100 000 person-years and prevalence, 3.67 (95% CI, 3.05-4.43). FTD incidence among individuals younger than 65 years was 1.84 (95% CI, 0.79-4.30) per 100 000 person-years and prevalence, 7.47 (95% CI, 4.13-13.49) per 100 000 people. The denominator based on census data showed less heterogeneity than the population at risk defined by the authors ( I ² : for incidence, 91.6% vs 97.6%, respectively, and for prevalence, 98.8% vs 99.2%, respectively). Conclusions and Relevance: In this systematic review and meta-analysis, estimates indicate that FTD is comparable in frequency to dementia with Lewy bodies and occurs at higher rates than progressive supranuclear palsy, corticobasal syndrome, and amyotrophic lateral sclerosis. These results provide a foundation for future research and public health strategy, especially for underrepresented populations, to better comprehend the global burden of FTD. Our findings provide robust pooled estimates of the incidence and prevalence of FTD and its subtypes, offering a foundation for future research and public health planning.