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A diagnosis of diabetes mellitus and prediabetes has been associated with increased risk of Parkinson’s disease (PD) in several studies, but results have not been entirely consistent. We conducted a systematic review and meta-analysis of cohort studies on diabetes mellitus, prediabetes and the risk of PD to provide an up-to-date assessment of the evidence. PubMed and Embase databases were searched for relevant studies up to 6th of February 2022. Cohort studies reporting adjusted relative risk (RR) estimates and 95% confidence intervals (CIs) for the association between diabetes, prediabetes and Parkinson’s disease were included. Summary RRs (95% CIs) were calculated using a random effects model. Fifteen cohort studies (29.9 million participants, 86,345 cases) were included in the meta-analysis. The summary RR (95% CI) of PD for persons with diabetes compared to persons without diabetes was 1.27 (1.20–1.35, I 2  = 82%). There was no indication of publication bias, based on Egger’s test (p = 0.41), Begg’s test (p = 0.99), and inspection of the funnel plot. The association was consistent across geographic regions, by sex, and across several other subgroup and sensitivity analyses. There was some suggestion of a stronger association for diabetes patients reporting diabetes complications than for diabetes patients without complications (RR = 1.54, 1.32–1.80 [n = 3] vs. 1.26, 1.16–1.38 [n = 3]), vs. those without diabetes (p heterogeneity =0.18). The summary RR for prediabetes was 1.04 (95% CI: 1.02–1.07, I 2  = 0%, n = 2). Our results suggest that patients with diabetes have a 27% increased relative risk of developing PD compared to persons without diabetes, and persons with prediabetes have a 4% increase in RR compared to persons with normal blood glucose. Further studies are warranted to clarify the specific role age of onset or duration of diabetes, diabetic complications, glycaemic level and its long-term variability and management may play in relation to PD risk.

China is increasingly facing the challenge of control of the growing burden of non-communicable diseases. We assessed the epidemiology of Alzheimer's disease and other forms of dementia in China between 1990, and 2010, to improve estimates of the burden of disease, analyse time trends, and inform health policy decisions relevant to China's rapidly ageing population. In our systematic review we searched for reports of Alzheimer's disease or dementia in China, published in Chinese and English between 1990 and 2010. We searched China National Knowledge Infrastructure, Wanfang, and PubMed databases. Two investigators independently assessed case definitions of Alzheimer's disease and dementia: we excluded studies that did not use internationally accepted case definitions. We also excluded reviews and viewpoints, studies with no numerical estimates, and studies not done in mainland China. We used Poisson regression and UN demographic data to estimate the prevalence (in nine age groups), incidence, and standardised mortality ratio of dementia and its subtypes in China in 1990, 2000, and 2010. Our search returned 12 642 reports, of which 89 met the inclusion criteria (75 assessed prevalence, 13 incidence, and nine mortality). In total, the included studies had 340 247 participants, in which 6357 cases of Alzheimer's disease were recorded. 254 367 people were assessed for other forms of dementia, of whom 3543 had vascular dementia, frontotemporal dementia, or Lewy body dementia. In 1990 the prevalence of all forms of dementia was 1·8% (95% CI 0·0–44·4) at 65–69 years, and 42·1% (0·0–88·9) at age 95–99 years. In 2010 prevalence was 2·6% (0·0–28·2) at age 65–69 years and 60·5% (39·7–81·3) at age 95–99 years. The number of people with dementia in China was 3·68 million (95% CI 2·22–5·14) in 1990, 5·62 million (4·42–6·82) in 2000, and 9·19 million (5·92–12·48) in 2010. In the same period, the number of people with Alzheimer's disease was 1·93 million (1·15–2·71) in 1990, 3·71 million (2·84–4·58) people in 2000, and 5·69 million (3·85–7·53) in 2010. The incidence of dementia was 9·87 cases per 1000 person-years, that of Alzheimer's disease was 6·25 cases per 1000 person-years, that of vascular dementia was 2·42 cases per 1000 person-years, and that of other rare forms of dementia was 0·46 cases per 1000 person-years. We retrieved mortality data for 1032 people with dementia and 20 157 healthy controls, who were followed up for 3–7 years. The median standardised mortality ratio was 1·94:1 (IQR 1·74–2·45). Our analysis suggests that previous estimates of dementia burden, based on smaller datasets, might have underestimated the burden of dementia in China. The burden of dementia seems to be increasing faster than is generally assumed by the international health community. Rapid and effective government responses are needed to tackle dementia in low-income and middle-income countries. Nossal Institute of Global Health (University of Melbourne, Australia), the National 12th Five-Year Major Projects of China, National Health and Medical Research Council Australia–China Exchange Fellowship, Importation and Development of High-Calibre Talents Project of Beijing Municipal Institutions, and the Bill & Melinda Gates Foundation.

Prions are proteins that adopt alternative conformations that become self-propagating; the PrPScprion causes the rare human disorder Creutzfeldt–Jakob disease (CJD). We report here that multiple system atrophy (MSA) is caused by a different human prion composed of the α-synuclein protein. MSA is a slowly evolving disorder characterized by progressive loss of autonomic nervous system function and often signs of parkinsonism; the neuropathological hallmark of MSA is glial cytoplasmic inclusions consisting of filaments of α-synuclein. To determine whether human α-synuclein forms prions, we examined 14 human brain homogenates for transmission to cultured human embryonic kidney (HEK) cells expressing full-length, mutant human α-synuclein fused to yellow fluorescent protein (α-syn140*A53T–YFP) and TgM83+/−mice expressing α-synuclein (A53T). The TgM83+/−mice that were hemizygous for the mutant transgene did not develop spontaneous illness; in contrast, the TgM83+/+mice that were homozygous developed neurological dysfunction. Brain extracts from 14 MSA cases all transmitted neurodegeneration to TgM83+/−mice after incubation periods of ∼120 d, which was accompanied by deposition of α-synuclein within neuronal cell bodies and axons. All of the MSA extracts also induced aggregation of α-syn*A53T–YFP in cultured cells, whereas none of six Parkinson’s disease (PD) extracts or a control sample did so. Our findings argue that MSA is caused by a unique strain of α-synuclein prions, which is different from the putative prions causing PD and from those causing spontaneous neurodegeneration in TgM83+/+mice. Remarkably, α-synuclein is the first new human prion to be identified, to our knowledge, since the discovery a half century ago that CJD was transmissible.

Objectives To quantify the associations between shielding status and loneliness at the start of the COVID-19 pandemic, and physical activity (PA) levels throughout the pandemic. Methods Demographic, health and lifestyle characteristics of 7748 cognitively healthy adults aged >50, and living in London, were surveyed from April 2020 to March 2021. The International Physical Activity Questionnaire (IPAQ) short-form assessed PA before COVID-19 restrictions, and up to 6 times over 11 months. Linear mixed models investigated associations between shielding status and loneliness at the onset of the pandemic, with PA over time. Results Participants who felt 'often lonely' at the outset of the pandemic completed an average of 522 and 547 fewer Metabolic Equivalent of Task (MET) minutes/week during the pandemic (95% CI: -809, -236, p<0.001) (95% CI: -818, -275, p<0.001) than those who felt 'never lonely' in univariable and multivariable models adjusted for demographic factors respectively. Those who felt 'sometimes lonely' completed 112 fewer MET minutes/week (95% CI: -219, -5, p = 0.041) than those who felt 'never lonely' following adjustment for demographic factors. Participants who were shielding at the outset of the pandemic completed an average of 352 fewer MET minutes/week during the pandemic than those who were not (95% CI: -432, -273; p<0.001) in univariable models and 228 fewer MET minutes/week (95% CI: -307, -150, p<0.001) following adjustment for demographic factors. No significant associations were found after further adjustment for health and lifestyle factors. Conclusions Those shielding or lonely at pandemic onset were likely to have completed low levels of PA during the pandemic. These associations are influenced by co-morbidities and health status.

Increasingly, evidence argues that many neurodegenerative diseases, including progressive supranuclear palsy (PSP), are caused by prions, which are alternatively folded proteins undergoing selfpropagation. In earlier studies, PSP prions were detected by infecting human embryonic kidney (HEK) cells expressing a tau fragment [TauRD(LM)] fused to yellow fluorescent protein (YFP). Here, we report on an improved bioassay using selective precipitation of tau prions from human PSP brain homogenates before infection of the HEK cells. Tau prions were measured by counting the number of cells with TauRD(LM)–YFP aggregates using confocal fluorescence microscopy. In parallel studies, we fused α-synuclein to YFP to bioassay α-synuclein prions in the brains of patients who died of multiple system atrophy (MSA). Previously, MSA prion detection required ∼120 d for transmission into transgenic mice, whereas our cultured cell assay needed only 4 d. Variation in MSA prion levels in four different brain regions from three patients provided evidence for three different MSA prion strains. Attempts to demonstrate α-synuclein prions in brain homogenates from Parkinson’s disease patients were unsuccessful, identifying an important biological difference between the two synucleinopathies. Partial purification of tau and α-synuclein prions facilitated measuring the levels of these protein pathogens in human brains. Our studies should facilitate investigations of the pathogenesis of both tau and α-synuclein prion disorders as well as help decipher the basic biology of those prions that attack the CNS.

We report a genome-wide assessment of single nucleotide polymorphisms (SNPs) and copy number variants (CNVs) in schizophrenia. We investigated SNPs using 871 patients and 863 controls, following up the top hits in four independent cohorts comprising 1,460 patients and 12,995 controls, all of European origin. We found no genome-wide significant associations, nor could we provide support for any previously reported candidate gene or genome-wide associations. We went on to examine CNVs using a subset of 1,013 cases and 1,084 controls of European ancestry, and a further set of 60 cases and 64 controls of African ancestry. We found that eight cases and zero controls carried deletions greater than 2 Mb, of which two, at 8p22 and 16p13.11-p12.4, are newly reported here. A further evaluation of 1,378 controls identified no deletions greater than 2 Mb, suggesting a high prior probability of disease involvement when such deletions are observed in cases. We also provide further evidence for some smaller, previously reported, schizophrenia-associated CNVs, such as those in NRXN1 and APBA2. We could not provide strong support for the hypothesis that schizophrenia patients have a significantly greater \"load\" of large (>100 kb), rare CNVs, nor could we find common CNVs that associate with schizophrenia. Finally, we did not provide support for the suggestion that schizophrenia-associated CNVs may preferentially disrupt genes in neurodevelopmental pathways. Collectively, these analyses provide the first integrated study of SNPs and CNVs in schizophrenia and support the emerging view that rare deleterious variants may be more important in schizophrenia predisposition than common polymorphisms. While our analyses do not suggest that implicated CNVs impinge on particular key pathways, we do support the contribution of specific genomic regions in schizophrenia, presumably due to recurrent mutation. On balance, these data suggest that very few schizophrenia patients share identical genomic causation, potentially complicating efforts to personalize treatment regimens.

Prions are proteins that adopt alternative conformations, which become self-propagating. Increasing evidence argues that prions feature in the synucleinopathies that include Parkinson's disease, Lewy body dementia, and multiple system atrophy (MSA). Although TgM83+/+ mice homozygous for a mutant A53T α-synuclein transgene begin developing CNS dysfunction spontaneously at ∼10 mo of age, uninoculated TgM83+/- mice (hemizygous for the transgene) remain healthy. To determine whether MSA brains contain α-synuclein prions, we inoculated the TgM83+/- mice with brain homogenates from two pathologically confirmed MSA cases. Inoculated TgM83+/- mice developed progressive signs of neurologic disease with an incubation period of ∼100 d, whereas the same mice inoculated with brain homogenates from spontaneously ill TgM83+/+ mice developed neurologic dysfunction in ∼210 d. Brains of MSA-inoculated mice exhibited prominent astrocytic gliosis and microglial activation as well as widespread deposits of phosphorylated α-synuclein that were proteinase K sensitive, detergent insoluble, and formic acid extractable. Our results provide compelling evidence that α-synuclein aggregates formed in the brains of MSA patients are transmissible and, as such, are prions. The MSA prion represents a unique human pathogen that is lethal upon transmission to Tg mice and as such, is reminiscent of the prion causing kuru, which was transmitted to chimpanzees nearly 5 decades ago.

Previously, we reported that intracranial inoculation of brain homogenate from multiple system atrophy (MSA) patient samples produces neurological disease in the transgenic (Tg) mouse model TgM83+/−, which uses the prion protein promoter to express human α-synuclein harboring the A53T mutation found in familial Parkinson’s disease (PD). In our studies, we inoculated MSA and control patient samples into Tg mice constructed using a P1 artificial chromosome to express wild-type (WT), A30P, and A53T human α-synuclein on a mouse α-synuclein knockout background [Tg(SNCA+/+)Nbm, Tg(SNCA*A30P+/+)Nbm, and Tg(SNCA*A53T+/+)Nbm]. In contrast to studies using TgM83+/− mice, motor deficits were not observed by 330–400 days in any of the Tg(SNCA)Nbm mice after inoculation with MSA brain homogenates. However, using a cell-based bioassay to measure α-synuclein prions, we found brain homogenates from Tg(SNCA*A53T+/+)Nbm mice inoculated with MSA patient samples contained α-synuclein prions, whereas control mice did not. Moreover, these α-synuclein aggregates retained the biological and biochemical characteristics of the α-synuclein prions in MSA patient samples. Intriguingly, Tg(SNCA*A53T+/+)Nbm mice developed α-synuclein pathology in neurons and astrocytes throughout the limbic system. This finding is in contrast to MSA-inoculated TgM83+/− mice, which develop exclusively neuronal α-synuclein aggregates in the hindbrain that cause motor deficits with advanced disease. In a crossover experiment, we inoculated TgM83+/− mice with brain homogenate from two MSA patient samples or one control sample first inoculated, or passaged, in Tg(SNCA*A53T+/+)Nbm animals. Additionally, we performed the reverse experiment by inoculating Tg(SNCA*A53T+/+)Nbm mice with brain homogenate from the same two MSA samples and one control sample first passaged in TgM83+/− animals. The TgM83+/− mice inoculated with mouse-passaged MSA developed motor dysfunction and α-synuclein prions, whereas the mouse-passaged control sample had no effect. Similarly, the mouse-passaged MSA samples induced α-synuclein prion formation in Tg(SNCA*A53T+/+)Nbm mice, but the mouse-passaged control sample did not. The confirmed transmission of α-synuclein prions to a second synucleinopathy model and the ability to propagate prions between two distinct mouse lines while retaining strain-specific properties provides compelling evidence that MSA is a prion disease.

The APOE ε4 allele is the most validated genetic risk factor for Alzheimer's disease and elevated amyloid burden is an early and key neuropathological feature of the disease. However, the mechanisms linking APOE ε4 to amyloid burden remain unclear. We aimed to investigate the organ-specific protein-protein interaction networks linking APOE ε4 carriage and amyloid elevation. Plasma levels of 7,301 aptamers (6,355 human proteins) were measured in 406 cognitively unimpaired adults (60-86 years, 51% female, 50% with elevated amyloid) from the Chariot PRO study via the SomaScan assay v4.1. Proteins were assigned to nine organ-system-based groups using the Human Protein Atlas. For each group, we fitted elastic net models (including age, sex, BMI, and storage duration) to classify APOE ε4 carriage and amyloid elevation (determined through predefined cut-offs using PET or CSF measurements) separately, repeating modelling 50 times and retaining proteins selected at least once. STRING-based protein-protein networks were constructed with the proteins selected for each group on both APOE ε4 carriage and amyloid elevation classification. Classification accuracy of both APOE ε4 carriage status and Amyloid elevation was significantly enhanced by the Inclusion of proteins from the immune or nervous systems in the model: 93.5% vs 93.7% for the former and 62.6% vs 61.0% for the latter. 15 proteins from the immune system (CEACAM3, MYC, CD80, CXCL10, ITGA4, and SPC25) and the nervous system (GAD1, CPLX2, RAB37, ADCYAP1, VAMP2, CCK, CPLX1, MPZ, and COL2A1) emerged as the most powerful discriminators of APOE ε4 carriage and amyloid elevation with high network centrality. Notably, along with brain enriched proteins included in the nervous system, proteins enriched in immune system emerged as the most powerful discriminators of both APOE ε4 carriage and amyloid elevation. By integrating network centrality metrics with machine-learning classification, we have identified 15 plasma proteins that show strong associations with both APOE ε4 carriage and amyloid elevation. Our findings may contribute to understanding of biological process linking APOE ε4 genotype and elevated amyloid burden and highlight the importance of immunological mechanisms in Alzheimer's pathology.

Metformin, a diabetes drug with anti-aging cellular responses, has complex actions that may alter dementia onset. Mixed results are emerging from prior observational studies. To address this complexity, we deploy a causal inference approach accounting for the competing risk of death in emulated clinical trials using two distinct electronic health record systems. In intention-to-treat analyses, metformin use associates with lower hazard of all-cause mortality and lower cause-specific hazard of dementia onset, after accounting for prolonged survival, relative to sulfonylureas. In parallel systems pharmacology studies, the expression of two AD-related proteins, APOE and SPP1, was suppressed by pharmacologic concentrations of metformin in differentiated human neural cells, relative to a sulfonylurea. Together, our findings suggest that metformin might reduce the risk of dementia in diabetes patients through mechanisms beyond glycemic control, and that SPP1 is a candidate biomarker for metformin’s action in the brain. Previous observational studies of the diabetes drugs metformin vs. sulfonylureas have yielded mixed results about whether metformin reduces the risk of dementia, relative to the sulfonylureas. Here, the authors apply a novel competing risks approach to emulate dementia-related target trials in electronic health records of diabetic patients and a complementary systems pharmacology evaluation on human neural cells.