Objective To predict the global, regional, and national prevalence of Parkinson’s disease by age, sex, year, and Socio-demographic Index to 2050 and quantify the factors driving changes in Parkinson’s disease cases. Design Modelling study. Data source Global Burden of Disease Study 2021. Main outcome measures Prevalent number, all age prevalence and age standardised prevalence of Parkinson’s disease in 2050, and average annual percentage change of prevalence from 2021 to 2050; contribution of population ageing, population growth, and changes in prevalence to the growth in Parkinson’s disease cases; population attributable fractions for modifiable factors. Results 25.2 (95% uncertainty interval 21.7 to 30.1) million people were projected to be living with Parkinson’s disease worldwide in 2050, representing a 112% (95% uncertainty interval 71% to 152%) increase from 2021. Population ageing (89%) was predicted to be the primary contributor to the growth in cases from 2021 to 2050, followed by population growth (20%) and changes in prevalence (3%). The prevalence of Parkinson’s disease was forecasted to be 267 (230 to 320) cases per 100 000 in 2050, indicating a significant increase of 76% (56% to 125%) from 2021, whereas the age standardised prevalence was predicted to be 216 (168 to 281) per 100 000, with an increase of 55% (50% to 60%) from 2021. Countries in the middle fifth of Socio-demographic Index were projected to have the highest percentage increase in the all age prevalence (144%, 87% to 183%) and age standardised prevalence (91%, 82% to 101%) of Parkinson’s disease between 2021 and 2050. Among Global Burden of Disease regions, East Asia (10.9 (9.0 to 13.3) million) was projected to have the highest number of Parkinson’s disease cases in 2050, with western Sub-Saharan Africa (292%, 266% to 362%) experiencing the most significant increase from 2021. The ≥80 years age group was projected to have the greatest increase in the number of Parkinson’s disease cases (196%, 143% to 235%) from 2021 to 2050. The male-to-female ratios of age standardised prevalence of Parkinson’s disease were projected to increase from 1.46 in 2021 to 1.64 in 2050 globally. Conclusions By 2050 Parkinson’s disease will have become a greater public health challenge for patients, their families, care givers, communities, and society. The upward trend is expected to be more pronounced among countries with middle Socio-demographic Index, in the Global Burden of Disease East Asia region, and among men. This projection could serve as an aid in promoting health research, informing policy decisions, and allocating resources.

Parkinson's disease is the second most common neurodegenerative disorder, exhibiting an upward trend in prevalence. We aimed to investigate the prevalence of Parkinson's disease, temporal trends between 1980 and 2023, and variations in prevalence by location, age, sex, survey period, sociodemographic index (SDI), human development index (HDI), and study characteristics (sample size, diagnostic criteria, and data source). In this systematic review and meta-analysis we searched PubMed, Cochrane, Web of Science, Embase, Scopus, and Global Health for observational studies that reported Parkinson's disease prevalence in the general population from database inception to Nov 1, 2023. We included studies if they were original observational investigations, had participants from the general population or community-based datasets, and provided numerical data on the prevalence of Parkinson's disease either with 95% CIs or with sufficient information to calculate 95% CIs. Studies were excluded if they were conducted in a specific population, had a sample size smaller than 1000, or were review articles, case reports, protocols, meeting abstracts, letters, comments, short communications, posters, and reports. The publication characteristics (first author and publication year), study location (countries, WHO regions, SDI, and HDI), survey period, study design, diagnostic criteria, data source, participant information, and prevalence data were extracted from articles using a standard form. Two authors independently evaluated eligibility, and discrepancies were resolved through discussion with the third author. We used random effect models to pool estimates with 95% CIs. Estimated annual percentage change (EAPC) was calculated to assess the temporal trend in prevalence of Parkinson's disease. The study was registered with PROSPERO, CRD42022364417. 83 studies from 37 countries were eligible for analysis, with 56 studies providing all-age prevalence, 53 studies reporting age-specific prevalence, and 26 studies providing both all-age and age-specific prevalence. Global pooled prevalence of Parkinson's disease was 1·51 cases per 1000 (95% CI 1·19-1·88), which was higher in males (1·54 cases per 1000 [1·17-1·96]) than in females (1·49 cases per 1000 [1·12-1·92], p=0·030). During different survey periods, the prevalence of Parkinson's disease was 0·90 cases per 1000 (0·48-1·44; 1980-89), 1·38 cases per 1000 (1·17-1·61; 1990-99), 1·18 cases per 1000 (0·77-1·67; 2000-09), and 3·81 cases per 1000 (2·67-5·14; 2010-23). The EAPC of Parkinson's disease prevalence was significantly higher in the period of 2004-23 (EAPC 16·32% [95% CI 6·07-26·58], p=0·0040) than in the period of 1980-2003 (5·30% [0·82-9·79], p=0·022). Statistically significant disparities in prevalence were observed across six WHO regions. Prevalence increased with HDI or SDI. Considerable variations were observed in the pooled prevalence of Parkinson's disease based on different sample sizes or diagnostic criteria. Prevalence also increased with age, reaching 9·34 cases per 1000 (7·26-11·67) among individuals older than 60 years. The global prevalence of Parkinson's disease has been increasing since the 1980s, with a more pronounced rise in the past two decades. The prevalence of Parkinson's disease is higher in countries with higher HDI or SDI. It is necessary to conduct more high-quality epidemiological studies on Parkinson's disease, especially in low SDI countries. National Nature Science Foundation of China. For the Chinese translation of the abstract see Supplementary Materials section.

Erythrocytes are a major source of peripheral α-synuclein (α-Syn). The goal of the current investigation is to evaluate erythrocytic total, oligomeric/aggregated, and phosphorylated α-Syn species as biomarkers of Parkinson’s disease (PD). PD and healthy control blood samples were collected along with extensive clinical history to determine whether total, phosphorylated, or aggregated α-Syn derived from erythrocytes (the major source of blood α-Syn) are more promising and consistent biomarkers for PD than are free α-Syn species in serum or plasma. Using newly developed electrochemiluminescence assays, concentrations of erythrocytic total, aggregated and phosphorylated at Ser129 (pS129) α-Syn, separated into membrane and cytosolic components, were measured in 225 PD patients and 133 healthy controls and analyzed with extensive clinical measures. The total and aggregated α-Syn levels were significantly higher in the membrane fraction of PD patients compared to healthy controls, but without alterations in the cytosolic component. The pS129 level was remarkably higher in PD subjects than in controls in the cytosolic fraction, and to a lesser extent, higher in the membrane fraction. Combining age, erythrocytic membrane aggregated α-Syn, and cytosolic pS129 levels, a model generated by using logistic regression analysis was able to discriminate patients with PD from neurologically normal controls, with a sensitivity and a specificity of 72 and 68%, respectively. These results suggest that total, aggregated and phosphorylated α-Syn levels are altered in PD erythrocytes and peripheral erythrocytic α-Syn is a potential PD biomarker that needs further validation.