Parkinson disease and smoking revisited: ease of quitting is an early sign of the disease

Yeast Models for Amyloids and Prions: Environmental Modulation and Drug Discovery

Amyloids are self-perpetuating protein aggregates causing neurodegenerative diseases in mammals. Prions are transmissible protein isoforms (usually of amyloid nature). Prion features were recently reported for various proteins involved in amyloid and neural inclusion disorders. Heritable yeast prions share molecular properties (and in the case of polyglutamines, amino acid composition) with human disease-related amyloids. Fundamental protein quality control pathways, including chaperones, the ubiquitin proteasome system and autophagy are highly conserved between yeast and human cells. Crucial cellular proteins and conditions influencing amyloids and prions were uncovered in the yeast model. The treatments available for neurodegenerative amyloid-associated diseases are few and their efficiency is limited. Yeast models of amyloid-related neurodegenerative diseases have become powerful tools for high-throughput screening for chemical compounds and FDA-approved drugs that reduce aggregation and toxicity of amyloids. Although some environmental agents have been linked to certain amyloid diseases, the molecular basis of their action remains unclear. Environmental stresses trigger amyloid formation and loss, acting either via influencing intracellular concentrations of the amyloidogenic proteins or via heterologous inducers of prions. Studies of environmental and physiological regulation of yeast prions open new possibilities for pharmacological intervention and/or prophylactic procedures aiming on common cellular systems rather than the properties of specific amyloids.

The interplay of aging, genetics and environmental factors in the pathogenesis of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by dopaminergic neuronal loss in the substantia nigra pars compacta and intracellular inclusions called Lewy bodies (LB). During the course of disease, misfolded α-synuclein, the major constituent of LB, spreads to different regions of the brain in a prion-like fashion, giving rise to successive non-motor and motor symptoms. Etiology is likely multifactorial, and involves interplay among aging, genetic susceptibility and environmental factors.

MAIN BODY

The prevalence of PD rises exponentially with age, and aging is associated with impairment of cellular pathways which increases susceptibility of dopaminergic neurons to cell death. However, the majority of those over the age of 80 do not have PD, thus other factors in addition to aging are needed to cause disease. Discovery of neurotoxins which can result in parkinsonism led to efforts in identifying environmental factors which may influence PD risk. Nevertheless, the causality of most environmental factors is not conclusively established, and alternative explanations such as reverse causality and recall bias cannot be excluded. The lack of geographic clusters and conjugal cases also go against environmental toxins as a major cause of PD. Rare mutations as well as common variants in genes such as SNCA, LRRK2 and GBA are associated with risk of PD, but Mendelian causes collectively only account for 5% of PD and common polymorphisms are associated with small increase in PD risk. Heritability of PD has been estimated to be around 30%. Thus, aging, genetics and environmental factors each alone is rarely sufficient to cause PD for most patients.

CONCLUSION

PD is a multifactorial disorder involving interplay of aging, genetics and environmental factors. This has implications on the development of appropriate animal models of PD which take all these factors into account. Common converging pathways likely include mitochondrial dysfunction, impaired autophagy, oxidative stress and neuroinflammation, which are associated with the accumulation and spread of misfolded α-synuclein and neurodegeneration. Understanding the mechanisms involved in the initiation and progression of PD may lead to potential therapeutic targets to prevent PD or modify its course.

Fibromyalgia-Like Syndrome Associated with Parkinson's Disease-A Cohort Study

Parkinson’s disease (PD) and fibromyalgia (FM) are two relatively common disorders that are considered distinct diagnoses. The aim of this study was to investigate the epidemiological characteristics of patients with both PD and FM, as well as their comorbidities and medication use. We performed a population-based retrospective cohort study in Israel from 2000 to 2015. We identified patients with PD according to a refined medication tracer algorithm and patients with FM according to their medical records. Using the algorithm, we identified 2606 patients diagnosed with PD, 60 of them (2.3%) were also diagnosed with FM. Most of the patients were females (88.3%) and the mean age of FM diagnosis was 63.95 ± 12.27 years. These patients had a higher prevalence of depression, anxiety, and dementia. Of the patients diagnosed with PD + FM, 46 (76.7%) were diagnosed with FM after the diagnosis of PD. Patients with PD + FM used analgesics of distinct kinds in higher rates, as well as more anti-PD medications. We suggest that patients with PD + FM represent a distinct subgroup with a fibromyalgia-like syndrome associated with Parkinson’s disease (FLISPAD). Their PD is more treatment resistant, and they take more medications, both analgesics and anti-PD.

Exploring causality of the association between smoking and Parkinson's disease

BACKGROUND

The aim of this paper is to investigate the causality of the inverse association between cigarette smoking and Parkinson's disease (PD). The main suggested alternatives include a delaying effect of smoking, reverse causality or an unmeasured confounding related to a low-risk-taking personality trait.

METHODS

A total of 715 incident PD cases were ascertained in a cohort of 220 494 individuals from NeuroEPIC4PD, a prospective European population-based cohort study including 13 centres in eight countries. Smoking habits were recorded at recruitment. We analysed smoking status, duration, and intensity and exposure to passive smoking in relation to PD onset.

RESULTS

Former smokers had a 20% decreased risk and current smokers a halved risk of developing PD compared with never smokers. Strong dose-response relationships with smoking intensity and duration were found. Hazard ratios (HRs) for smoking <20 years were 0.84 [95% confidence interval (CI) 0.67-1.07], 20-29 years 0.73 (95% CI 0.56-0.96) and >30 years 0.54 (95% CI 0.43-0.36) compared with never smokers. The proportional hazard assumption was verified, showing no change of risk over time, arguing against a delaying effect. Reverse causality was disproved by the consistency of dose-response relationships among former and current smokers. The inverse association between passive smoking and PD, HR 0.70 (95% CI 0.49-0.99) ruled out the effect of unmeasured confounding.

CONCLUSIONS

These results are highly suggestive of a true causal link between smoking and PD, although it is not clear which is the chemical compound in cigarette smoking responsible for the biological effect.

Genetic variants in nicotinic receptors and smoking cessation in Parkinson's disease

BACKGROUND

Negative associations between smoking and Parkinson's disease (PD) are well documented. While common biases may not explain this association, some studies have suggested reverse causality and ease of quitting might be an early sign of PD, possibly related to a reduced nicotinic response. We investigated nicotinic receptor (nAChR) genetics to add to our understanding of possible biologic mechanisms underlying the smoking-PD relationship.

METHODS

We relied on 612 patients and 691 controls enrolled in the PEG (Parkinson's Environment and Gene) study for whom we obtained information on smoking and quitting ease through interviews. Genotyping in the nAChR genes, i.e. CHRNA5-A3-B4 and CHRNB3-A6 gene regions that have been linked to smoking or quitting behaviors, were based on blood and saliva DNA samples. We assessed associations with logistic regression assuming logit-additive allelic effects and used product terms for genetic allele status and smoking or quitting assessing interactions.

RESULTS

As expected, we observed negative associations between smoking and PD that were strongest for current followed by former smokers. In former smokers, high quitting difficulty was negatively associated with PD risk (extremely hard vs. easy: OR = 0.62 [0.39-0.99], p = 0.05), meaning those who developed PD were able to quit smoking with less difficulty than controls. The CHRNA3 rs578776-A allele predicted quitting difficulty in smoking controls (OR = 0.53 [0.32-0.91], p = 0.02), but not in smoking PD patients (OR = 1.09 [0.61-1.95], p = 0.77).

CONCLUSION

Our study further corroborates previous findings that ease of quitting may be an early sign of PD onset related to a loss of nicotinic response in prodromal stages.

Cancers Preceding Parkinson's Disease after Adjustment for Bias in a Danish Population-Based Case-Control Study

Cancer patients are at lower risk of developing Parkinson's disease (PD) compared with the general population. One explanation is the negative association between smoking and PD, but PD risk is also lower for cancers not related to smoking. Another explanation is survival bias where death from cancer may act as a competing risk. We conducted a large population-based case-control study in Denmark and investigated whether cancer diagnosis reduced the risk of developing PD even after adjusting for important risk factors including smoking, physical activity, and lifetime oestrogen status. Using probabilistic bias analysis we quantified the influence of survival bias. We estimated negative point estimates (ORs) between cancers and PD for all cancers except skin, female breast, and ill-defined and unspecified 0.85 (95% CI 0.59-1.21); smoking-related cancers 0.75 (95% CI 0.45-1.23); and cancers not related to smoking 0.82 (95% CI 0.49-1.38) that are very similar to those previously reported for a much larger Danish register only based study, even though our confidence intervals include the null. These effect estimates shifted towards the null after accounting for survival bias but most bias-adjusted ORs remained below 1 within the range of priors considered in simulations. Overall, cancer patients have a lower risk of developing PD even after controlling for cancer-related lifestyles factors and correcting for survival bias.

The association between lifestyle factors and Parkinson's disease progression and mortality

BACKGROUND

Lifestyle factors may contribute to the development of Parkinson's disease, but little is known about factors that influence progression. The objective of the current study was to examine whether caffeine or alcohol consumption, physical activity, or cigarette smoking is associated with progression and survival among PD patients.

METHODS

We assessed lifelong coffee, tea, and alcohol consumption, smoking, and physical activity in a prospective community-based cohort (n = 360). All patients were passively followed for mortality (2001-2016); 244 were actively followed on average ± SD 5.3 ± 2.1 years (2007-2014). Movement disorder specialists repeatedly assessed motor function (Hoehn & Yahr) and cognition (Mini-Mental State Exam). We used Cox proportional hazards models and inverse probability weights to account for censoring.

RESULTS

Coffee, caffeinated tea, moderate alcohol consumption, and physical activity were protective against at least 1 outcome. Smoking and heavy alcohol consumption were associated with increased risks. Coffee was protective against time to Hoehn & Yahr stage 3 (hazard ratio, 0.52; 95% confidence interval, 0.28-1.01), cognitive decline (hazard ratio, 0.23; 95% confidence interval, 0.11, 0.48), and mortality (hazard ratio, 0.47; 95% confidence interval, 0.32-0.69). Relative to moderate drinkers, those who never drank liquor and those who drank more heavily were at an increased risk of Hoehn & Yahr 3 (hazard ratio, 3.48; 95% confidence interval, 1.90-6.38; and hazard ratio, 2.16; 95% confidence interval, 1.03, 4.54, respectively). A history of competitive sports was protective against cognitive decline (hazard ratio, 0.46; 95% confidence interval, 0.22-0.96) and Hoehn & Yahr 3 (hazard ratio, 0.42; 95% confidence interval, 0.23-0.79), as was physical activity measured by metabolic-equivalent hours. Current cigarette smoking was associated with faster cognitive decline (hazard ratio, 3.20; 95% confidence interval, 1.02-10.01).

CONCLUSIONS

This population-based study suggests that lifestyle factors influence PD progression and mortality. © 2019 International Parkinson and Movement Disorder Society.

Inflammatory Bowel Diseases and Parkinson's Disease

The etiology of Parkinson's disease (PD) is multifactorial, with genetics, aging, and environmental agents all a part of the PD pathogenesis. Widespread aggregation of the α-synuclein protein in the form of Lewy bodies and Lewy neurites, and degeneration of substantia nigra dopamine neurons are the pathological hallmarks of PD. Inflammatory responses manifested by glial reactions, T cell infiltration, and increased expression of inflammatory cytokines, as well as other toxic mediators derived from activated glial cells, are currently recognized as prominent features of PD. Experimental, clinical and epidemiological data suggest that intestinal inflammation contributes to the pathogenesis of PD, and the increasing number of studies suggests that the condition may start in the gastrointestinal system years before any motor symptoms develop. Patients with inflammatory bowel disease (IBD) have a higher risk of developing PD compared with non-IBD individuals. Gene association study has found a genetic link between IBD and PD, and an evidence from animal studies suggests that gut inflammation, similar to that observed in IBD, may induce loss of dopaminergic neurons. Based on preclinical models of PD, it is suggested that the enteric microbiome changes early in PD, and gut infections trigger α-synuclein release and aggregation. In this paper, the possible link between IBD and PD is reviewed based on the available literature. Given the potentially critical role of gastrointestinal pathology in PD pathogenesis, there is reason to suspect that IBD or its treatments may impact PD risk. Thus, clinicians should be aware of PD symptoms in IBD patients.

Increased risk of diseases of the basal ganglia and cerebellum in patients with a history of attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is marked by an ongoing pattern of inattention and/or hyperactivity and involves dysregulated dopaminergic pathways. Dopaminergic agents (i.e., amphetamine and methylphenidate) are thus prescribed to treat ADHD. As little is known regarding long-term consequences of either ADHD or its treatment, the objective of this study was to determine if either alters the risk of diseases of the basal ganglia and cerebellum, including Parkinson's disease. Statewide medical records from 1996 to 2016 were retrieved from the Utah Population Database to conduct a retrospective cohort study. Participants included ADHD patients (International Classification of Diseases, 9th revision (ICD-9) diagnosis codes 314.0-314.2, 314.8, 314.9) and 5:1 random sex-matched and age-matched subjects with no ADHD diagnosis history. Both patients and non-ADHD subjects met the following eligibility criteria: (1) no prior diagnosis of Parkinson's disease, secondary parkinsonism, basal ganglia disease, or essential tremor (ICD-9 codes 332.0, 332.1, 333.0, 333.1), (2) born in 1950 or later and age ≥20 years at last follow-up, and (3) no history of substance abuse (illicit drugs or alcohol). Outcomes were measured as time to diagnosis of diseases of the basal ganglia and cerebellum, death, or study-end. A Cox model incorporating a competing risk of death was used to provide hazard ratio estimates. Patients with ADHD (N = 31,769) had a 2.4-fold increased risk of basal ganglia and cerebellum diseases (95% confidence interval (CI): 2.0-3.0; P < 0.0001) compared with 158,790 non-ADHD persons, after controlling for sex and age and adjusting for tobacco use and psychotic conditions. In 4960 ADHD patients prescribed psychostimulants, risk of basal ganglia and cerebellum diseases between ages 21 and 49 years was especially pronounced, at 8.6-fold (95% CI: 4.8-15.6; P < 0001). The association of ADHD patients prescribed psychostimulants with higher risk of diseases of the basal ganglia and cerebellum may reflect a more severe ADHD phenotype rather than a direct association between prescribed stimulant use and basal ganglia or cerebellum disorders. Future studies to assess and stratify patient risk so as to inform treatment are warranted.

Nicotine promotes neuron survival and partially protects from Parkinson's disease by suppressing SIRT6

Parkinson’s disease is characterized by progressive death of dopaminergic neurons, leading to motor and cognitive dysfunction. Epidemiological studies consistently show that the use of tobacco reduces the risk of Parkinson’s. We report that nicotine reduces the abundance of SIRT6 in neuronal culture and brain tissue. We find that reduction of SIRT6 is partly responsible for neuroprotection afforded by nicotine. Additionally, SIRT6 abundance is greater in Parkinson’s patient brains, and decreased in the brains of tobacco users. We also identify SNPs that promote SIRT6 expression and simultaneously associate with an increased risk of Parkinson’s. Furthermore, brain-specific SIRT6 knockout mice are protected from MPTP-induced Parkinson’s, while SIRT6 overexpressing mice develop more severe pathology. Our data suggest that SIRT6 plays a pathogenic and pro-inflammatory role in Parkinson’s and that nicotine can provide neuroprotection by accelerating its degradation. Inhibition of SIRT6 may be a promising strategy to ameliorate Parkinson’s and neurodegeneration.

Global, regional, and national burden of Parkinson's disease, 1990-2016: a systematic analysis for the Global Burden of Disease Study 2016

BACKGROUND

Neurological disorders are now the leading source of disability globally, and ageing is increasing the burden of neurodegenerative disorders, including Parkinson's disease. We aimed to determine the global burden of Parkinson's disease between 1990 and 2016 to identify trends and to enable appropriate public health, medical, and scientific responses.

METHODS

Through a systematic analysis of epidemiological studies, we estimated global, regional, and country-specific prevalence and years of life lived with disability for Parkinson's disease from 1990 to 2016. We estimated the proportion of mild, moderate, and severe Parkinson's disease on the basis of studies that used the Hoehn and Yahr scale and assigned disability weights to each level. We jointly modelled prevalence and excess mortality risk in a natural history model to derive estimates of deaths due to Parkinson's disease. Death counts were multiplied by values from the Global Burden of Disease study's standard life expectancy to compute years of life lost. Disability-adjusted life-years (DALYs) were computed as the sum of years lived with disability and years of life lost. We also analysed results based on the Socio-demographic Index, a compound measure of income per capita, education, and fertility.

FINDINGS

In 2016, 6·1 million (95% uncertainty interval [UI] 5·0-7·3) individuals had Parkinson's disease globally, compared with 2·5 million (2·0-3·0) in 1990. This increase was not solely due to increasing numbers of older people, because age-standardised prevalence rates increased by 21·7% (95% UI 18·1-25·3) over the same period (compared with an increase of 74·3%, 95% UI 69·2-79·6, for crude prevalence rates). Parkinson's disease caused 3·2 million (95% UI 2·6-4·0) DALYs and 211 296 deaths (95% UI 167 771-265 160) in 2016. The male-to-female ratios of age-standardised prevalence rates were similar in 2016 (1·40, 95% UI 1·36-1·43) and 1990 (1·37, 1·34-1·40). From 1990 to 2016, age-standardised prevalence, DALY rates, and death rates increased for all global burden of disease regions except for southern Latin America, eastern Europe, and Oceania. In addition, age-standardised DALY rates generally increased across the Socio-demographic Index.

INTERPRETATION

Over the past generation, the global burden of Parkinson's disease has more than doubled as a result of increasing numbers of older people, with potential contributions from longer disease duration and environmental factors. Demographic and potentially other factors are poised to increase the future burden of Parkinson's disease substantially.

FUNDING

Bill & Melinda Gates Foundation.

Chronic nicotine improves cognitive and social impairment in mice overexpressing wild type α-synuclein

In addition to dopaminergic and motor deficits, patients with Parkinson's disease (PD) suffer from non-motor symptoms, including early cognitive and social impairment, that do not respond well to dopaminergic therapy. Cholinergic deficits may contribute to these problems, but cholinesterase inhibitors have limited efficacy. Mice over-expressing α-synuclein, a protein critically associated with PD, show deficits in cognitive and social interaction tests, as well as a decrease in cortical acetylcholine. We have evaluated the effects of chronic administration of nicotine in mice over-expressing wild type human α-synuclein under the Thy1-promoter (Thy1-aSyn mice). Nicotine was administered subcutaneously by osmotic minipump for 6 months from 2 to 8 months of age at 0.4 mg/kg/h and 2.0 mg/kg/h. The higher dose was toxic in the Thy1-aSyn mice, but the low dose was well tolerated and both doses ameliorated cognitive impairment in Y-maze performance after 5 months of treatment. In a separate cohort of Thy1-aSyn mice, nicotine was administered at the lower dose for one month beginning at 5 months of age. This treatment partially eliminated the cognitive deficit in novel object recognition and social impairment. In contrast, chronic nicotine did not improve motor deficits after 2, 4 or 6 months of treatment, nor modified α-synuclein aggregation, tyrosine hydroxylase immunostaining, synaptic and dendritic markers, or microglial activation in Thy1-aSyn mice. These results suggest that cognitive and social impairment in synucleinopathies like PD may result from deficits in cholinergic neurotransmission and may benefit from chronic administration of nicotinic agonists.

Moist smokeless tobacco (Snus) use and risk of Parkinson's disease

Background

Cigarette smoking is associated with a lower risk of Parkinson's disease. It is unclear what constituent of tobacco smoke may lower the risk. Use of Swedish moist smokeless tobacco (snus) can serve as a model to disentangle what constituent of tobacco smoke may lower the risk. The aim of this study was to determine whether snus use was associated with a lower risk of Parkinson's disease.

Methods

Individual participant data were collected from seven prospective cohort studies, including 348 601 men. We used survival analysis with multivariable Cox regression to estimate study-specific relative risk of Parkinson's disease due to snus use, and random-effects models to pool estimates in a meta-analysis. The primary analyses were restricted to never-smokers to eliminate the potential confounding effect of tobacco smoking.

Results

During a mean follow-up time of 16.1 years, 1199 incident Parkinson's disease cases were identified. Among men who never smoked, ever-snus users had about 60% lower Parkinson's disease risk compared with never-snus users [pooled hazard ratio (HR) 0.41, 95% confidence interval (CI) 0.28-0.61]. The inverse association between snus use and Parkinson's disease risk was more pronounced in current (pooled HR 0.38, 95% CI 0.23-0.63), moderate-heavy amount (pooled HR 0.41, 95% CI 0.19-0.90) and long-term snus users (pooled HR 0.44, 95% CI 0.24-0.83).

Conclusions

Non-smoking men who used snus had a substantially lower risk of Parkinson's disease. Results also indicated an inverse dose-response relationship between snus use and Parkinson's disease risk. Our findings suggest that nicotine or other components of tobacco leaves may influence the development of Parkinson's disease.

Mild TBI and risk of Parkinson disease: A Chronic Effects of Neurotrauma Consortium Study

OBJECTIVE

Our aim was to assess risk of Parkinson disease (PD) following traumatic brain injury (TBI), including specifically mild TBI (mTBI), among care recipients in the Veterans Health Administration.

METHODS

In this retrospective cohort study, we identified all patients with a TBI diagnosis in Veterans Health Administration databases from October 2002 to September 2014 and age-matched 1:1 to a random sample of patients without TBI. All patients were aged 18 years and older without PD or dementia at baseline. TBI exposure and severity were determined via detailed clinical assessments or ICD-9 codes using Department of Defense and Defense and Veterans Brain Injury Center criteria. Baseline comorbidities and incident PD more than 1 year post-TBI were identified using ICD-9 codes. Risk of PD after TBI was assessed using Cox proportional hazard models adjusted for demographics and medical/psychiatric comorbidities.

RESULTS

Among 325,870 patients (half with TBI; average age 47.9 ± 17.4 years; average follow-up 4.6 years), 1,462 were diagnosed with PD during follow-up. Compared to no TBI, those with TBI had higher incidence of PD (no TBI 0.31%, all-severity TBI 0.58%, mTBI 0.47%, moderate-severe TBI 0.75%). In adjusted models, all-severity TBI, mTBI, and moderate-severe TBI were associated with increased risk of PD (hazard ratio [95% confidence interval]: all-severity TBI 1.71 [1.53-1.92]; mTBI 1.56 [1.35-1.80]; moderate-severe TBI 1.83 [1.61-2.07]).

CONCLUSIONS

Among military veterans, mTBI is associated with 56% increased risk of PD, even after adjusting for demographics and medical/psychiatric comorbidities. This study highlights the importance of TBI prevention, long-term follow-up of TBI-exposed veterans, and the need to determine mechanisms and modifiable risk factors for post-TBI PD.

VEGF Signaling in Neurological Disorders

Vascular endothelial growth factor (VEGF) is a potent growth factor playing diverse roles in vasculogenesis and angiogenesis. In the brain, VEGF mediates angiogenesis, neural migration and neuroprotection. As a permeability factor, excessive VEGF disrupts intracellular barriers, increases leakage of the choroid plexus endothelia, evokes edema, and activates the inflammatory pathway. Recently, we discovered that a heparin binding epidermal growth factor like growth factor (HB-EGF)—a class of EGF receptor (EGFR) family ligands—contributes to the development of hydrocephalus with subarachnoid hemorrhage through activation of VEGF signaling. The objective of this review is to entail a recent update on causes of death due to neurological disorders involving cerebrovascular and age-related neurological conditions and to understand the mechanism by which angiogenesis-dependent pathological events can be treated with VEGF antagonisms. The Global Burden of Disease study indicates that cancer and cardiovascular disease including ischemic and hemorrhagic stroke are two leading causes of death worldwide. The literature suggests that VEGF signaling in ischemic brains highlights the importance of concentration, timing, and alternate route of modulating VEGF signaling pathway. Molecular targets distinguishing two distinct pathways of VEGF signaling may provide novel therapies for the treatment of neurological disorders and for maintaining lower mortality due to these conditions.

Cigarette smoking and glaucoma in the United States population

PurposeTo evaluate the association between cigarette smoking and glaucoma in the United States population.Patients and methodsUS civilian, non-institutionalized population from 2005 to 2008 administrations of the National Health and Nutrition Examination Survey that were ≥40 years of age with visual fields and optic disc photographs were included. Diagnosis of glaucoma was based on the Rotterdam criteria. Logistic regression modeling was performed to assess the association between glaucoma and smoking history, while controlling for age, gender, ethnicity, household income, alcohol consumption, diabetes, and hypertension.ResultsIn 3864 participants, 212 (5.5%) had glaucoma (corresponds to a population weighted glaucoma prevalence of 3.7% in a total of 83 570 127 subjects). Population weighted proportion of current smokers was 20.6% and ex-smokers was 28.3%. Participants with glaucoma were older (63.0±11.6 vs 56.1±11.2, P=0.002), likely to be male (57.1% vs 49.2%, P=0.03), to be Black (36.3% vs 20.7%, P<0.001), and to have diabetes (18.9% vs 12.4%, P=0.006) and hypertension (50.5% vs 39.7%, P=0.003). Current smokers had a lower odds of glaucoma compared to non-smokers (OR=0.61, 95% CI=0.41-0.88, P=0.009), and ex-smokers (OR=0.46, 95% CI=0.28-0.76, P=0.002). The effect estimates were similar in adjusted models, but not statistically significant. Among smokers, greater pack/day of smoking history was associated with statistically significantly higher odds of glaucoma (OR=1.70, 95% CI=1.08-2.67, P=0.02).ConclusionsAmong cigarette smokers, heavy smoking defined by greater number of pack of cigarettes smoked per day is associated with higher odds of glaucoma. Health care providers should include this association when counseling patients on their smoking habit.

The Search for Environmental Causes of Parkinson's Disease: Moving Forward

It is widely believed that environmental exposures contribute to the vast majority of late-onset sporadic Parkinson's disease (PD), alone or via interactions with genetic factors. The search for environmental causes of PD has however been hampered by lack of understanding the prodromal phase of PD development and the difficulties in exposure assessment during this prolonged period. On the other hand, the existence of this prodromal period, along with an increasingly better understanding of PD prodromal symptoms, provides an exciting opportunity to identify environmental factors that initiate PD pathogenesis and/or modify its progression. For prevention efforts, this prodromal stage is of a major interest. Targeting factors that enter the body via the nose or gut has become even more important since the discovery of α-synuclein aggregates in the enteric and olfactory nervous systems. In this paper, we speculate about novel research hypotheses and approaches that may help us better define the role of environment in PD etiology, especially during its extended and complex prodromal phase.

Smoking and age-at-onset of both motor and non-motor symptoms in Parkinson's disease

INTRODUCTION

Several evidence suggest that smoking may decrease the risk of Parkinson's disease and is associated with an older age-at-onset of motor signs. The relation between smoking and age-at-onset of non-motor symptoms has never been analyzed. Objective of the study is to evaluate whether smoking habit and pack-years of smoking are associated with a delay of age-at-onset of motor signs, and of some non-motor symptoms.

METHODS

The study population consisted of 262 consecutive parkinsonian patients. Information on relevant demographic/clinical data focused on motor signs, REM sleep behavior disorder, constipation, depression, and hyposmia. Patients were stratified according to smoking habit (ever-versus never-smoker) and number of pack-years of smoking was computed. Repeatability of data on age-at-onset was checked 6 months after the initial interview in a randomly recruited subsample.

RESULTS

Smoking habit and number of pack-years smoked were associated with an older in age-at-onset of motor signs, REM sleep behavior disorder and depression. By contrast, smoking did not affect age-at-onset of hyposmia and constipation.

CONCLUSION

information from this study confirms that smoking may be associated with an older age-at-onset of motor signs, and that a similar effect can be observed on some non-motor symptoms like REM sleep behavior and depression.

[Epidemiology and causes of Parkinson's disease]

Parkinson's disease (PD) is the second most common neurodegenerative disease and has a growing socioeconomic impact due to demographic changes in the industrial nations. There are several forms of PD, a fraction of which (<5%) are monogenic, i. e. caused by mutations in single genes. At present, six genes have been established for the clinically classical form of parkinsonism including three autosomal dominantly (SNCA, LRRK2, VPS35) and three autosomal recessively inherited ones (Parkin, PINK1, DJ-1). In addition, there are a plethora of genes causing atypical forms of parkinsonism. In contrast, idiopathic PD is of a multifactorial nature. Genome-wide association studies have established a total of 26 genetic loci for this form of the disease; however, for most of these loci the underlying functional genetic variants have not yet been identified and the respective disease mechanisms remain unresolved. Furthermore, there are a number of environmental and life style factors that are associated with idiopathic PD. Exposure to pesticides and possibly a history of head trauma represent genuine risk factors. Other PD-associated factors, such as smoking and intake of coffee and alcohol may not represent risk factors per se and the cause-effect relationship has not yet been elucidated for most of these factors. A patient with a positive family history and/or an early age of disease onset should undergo counseling with respect to a possible monogenic form of the disease. Disease prediction based on genetic, environmental and life style factors is not yet possible for idiopathic PD and potential gene-specific therapies are currently in the development or early testing phase.

Alzheimer's disease and cigarette smoke components: effects of nicotine, PAHs, and Cd(II), Cr(III), Pb(II), Pb(IV) ions on amyloid-β peptide aggregation

Cigarette smoking is a significant risk factor for Alzheimer's disease (AD), which is associated with extracellular brain deposits of amyloid plaques containing aggregated amyloid-β (Aβ) peptides. Aβ aggregation occurs via multiple pathways that can be influenced by various compounds. Here, we used AFM imaging and NMR, fluorescence, and mass spectrometry to monitor in vitro how Aβ aggregation is affected by the cigarette-related compounds nicotine, polycyclic aromatic hydrocarbons (PAHs) with one to five aromatic rings, and the metal ions Cd(II), Cr(III), Pb(II), and Pb(IV). All PAHs and metal ions modulated the Aβ aggregation process. Cd(II), Cr(III), and Pb(II) ions displayed general electrostatic interactions with Aβ, whereas Pb(IV) ions showed specific transient binding coordination to the N-terminal Aβ segment. Thus, Pb(IV) ions are especially prone to interact with Aβ and affect its aggregation. While Pb(IV) ions affected mainly Aβ dimer and trimer formation, hydrophobic toluene mainly affected formation of larger aggregates such as tetramers. The uncharged and hydrophilic nicotine molecule showed no direct interactions with Aβ, nor did it affect Aβ aggregation. Our Aβ interaction results suggest a molecular rationale for the higher AD prevalence among smokers, and indicate that certain forms of lead in particular may constitute an environmental risk factor for AD.

Pooled analysis of the HLA-DRB1 by smoking interaction in Parkinson disease

OBJECTIVE

Inflammatory response plays an important role in Parkinson disease (PD). Previous studies have reported an association between human leukocyte antigen (HLA)-DRB1 and the risk of PD. There has also been growing interest in investigating whether inflammation-related genes interact with environmental factors such as smoking to influence PD risk. We performed a pooled analysis of the interaction between HLA-DRB1 and smoking in PD in 3 population-based case-control studies from Denmark and France.

METHODS

We included 2,056 cases and 2,723 controls from 3 PD studies (Denmark, France) that obtained information on smoking through interviews. Genotyping of the rs660895 polymorphism in the HLA-DRB1 region was based on saliva or blood DNA samples. To assess interactions, we used logistic regression with product terms between rs660895 and smoking. We performed random-effects meta-analysis of marginal associations and interactions.

RESULTS

Both carrying rs660895-G (AG vs AA: odds ratio [OR] = 0.81; GG vs AA: OR = 0.56; p-trend = 0.003) and ever smoking (OR = 0.56, p < 0.001) were inversely associated with PD. A multiplicative interaction was observed between rs660895 and smoking using codominant, additive (interaction parameter = 1.37, p = 0.005), and dominant (interaction parameter = 1.54, p = 0.001) genetic models without any heterogeneity (I² = 0.0%); the inverse association of rs660895-(AG+GG) with PD seen in never smokers (OR = 0.64, p < 0.001) disappeared among ever smokers (OR = 1.00, p = 0.99). Similar interactions were observed when we investigated light and heavy smokers separately.

INTERPRETATION

Our study provides the first evidence that smoking modifies the previously reported inverse association of rs660895-G with PD, and suggests that smoking and HLA-DRB1 are involved in common pathways, possibly related to neuroinflammation. Ann Neurol 2017;82:655-664.

The neuroprotective effect of nicotine in Parkinson's disease models is associated with inhibiting PARP-1 and caspase-3 cleavage

Clinical evidence points to neuroprotective effects of smoking in Parkinson’s disease (PD), but the molecular mechanisms remain unclear. We investigated the pharmacological pathways involved in these neuroprotective effects, which could provide novel ideas for developing targeted neuroprotective treatments for PD. We used the ETC complex I inhibitor methylpyridinium ion (MPP⁺) to induce cell death in SH-SY5Y cells as a cellular model for PD and found that nicotine inhibits cell death. Using choline as a nicotinic acetylcholine receptor (nAChR) agonist, we found that nAChR stimulation was sufficient to protect SH-SY5Y cells against cell death from MPP⁺. Blocking α7 nAChR with methyllycaconitine (MLA) prevented the protective effects of nicotine, demonstrating that these receptors are necessary for the neuroprotective effects of nicotine. The neuroprotective effect of nicotine involves other pathways relevant to PD. Cleaved Poly (ADP-ribose) polymerase-1 (PARP-1) and cleaved caspase-3 were decreased by nicotine in 6-hydroxydopamine (6-OHDA) lesioned mice and in MPP⁺-treated SH-SY5Y cells. In conclusion, our data indicate that nicotine likely exerts neuroprotective effects in PD through the α7 nAChR and downstream pathways including PARP-1 and caspase-3. This knowledge could be pursued in future research to develop neuroprotective treatments for PD.

Caffeine as symptomatic treatment for Parkinson disease (Café-PD): A randomized trial

OBJECTIVE

To assess effects of caffeine on Parkinson disease (PD).

METHODS

In this multicenter parallel-group controlled trial, patients with PD with 1-8 years disease duration, Hoehn & Yahr stages I-III, on stable symptomatic therapy were randomized to caffeine 200 mg BID vs matching placebo capsules for 6-18 months. The primary research question was whether objective motor scores would differ at 6 months (Movement Disorder Society-sponsored Unified Parkinson's Disease Rating Scale [MDS-UPDRS]-III, Class I evidence). Secondary outcomes included safety and tolerability, motor symptoms (MDS-UPDRS-II), motor fluctuations, sleep, nonmotor symptoms (MDS-UPDRS-I), cognition (Montreal Cognitive Assessment), and quality of life.

RESULTS

Sixty patients received caffeine and 61 placebo. Caffeine was well-tolerated with similar prevalence of side effects as placebo. There was no improvement in motor parkinsonism (the primary outcome) with caffeine treatment compared to placebo (difference between groups -0.48 [95% confidence interval -3.21 to 2.25] points on MDS-UPDRS-III). Similarly, on secondary outcomes, there was no change in motor signs or motor symptoms (MDS-UPDRS-II) at any time point, and no difference on quality of life. There was a slight improvement in somnolence over the first 6 months, which attenuated over time. There was a slight increase in dyskinesia with caffeine (MDS-UPDRS-4.1+4.2 = 0.25 points higher), and caffeine was associated with worse cognitive testing scores (average Montreal Cognitive Assessment = 0.66 [0.01, 1.32] worse than placebo).

CONCLUSION

Caffeine did not provide clinically important improvement of motor manifestations of PD (Class I evidence). Epidemiologic links between caffeine and lower PD risk do not appear to be explained by symptomatic effects.

CLINICALTRIALSGOV IDENTIFIER

NCT01738178.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that for patients with PD, caffeine does not significantly improve motor manifestations.

Associations between Lifestyle Factors and Parkinson's Disease in an Urban Sri Lankan Clinic Study

BACKGROUND

Associations between certain environmental and lifestyle factors and Parkinson's disease (PD) have been reported in several studies, but information on these factors and Parkinson's Disease (PD) in South Asia, is limited.

OBJECTIVE

To determine associations between lifestyle factors and PD in an urban clinic-based study in Sri Lanka.

METHODS

In this case-control study, demographic and lifestyle factor data (including diet, coffee/tea drinking, smoking, alcohol status) was collected from an unselected cohort of PD patients and age and gender-matched controls attending clinics in Greater Colombo, Sri Lanka. Associations between lifestyle factors and PD status were assessed using Logistic Regression analysis, while links with age of PD onset were explored with Kaplan Meier and Cox Regression survival analyses. Results with p<0.05 were considered to be statistically significant.

FINDINGS

Of 229 patients with parkinsonism, 144 had Idiopathic PD using standard diagnostic criteria. Controls numbered 102. Coffee drinkers and smokers were significantly less likely to have PD (coffee, p<0.001; Odds Ratio (OR)=0.264; smoking, p=0.043; OR=0.394). Coffee drinkers were older at PD onset (p<0.001). Similar trends seen with tea drinking were not statistically significant.

CONCLUSIONS

This is the first formal study of PD and these lifestyle factors in South Asia. It demonstrates an inverse association between coffee drinking, smoking and PD, and an association between coffee drinking and later age of PD onset. This is in line with other studies done worldwide, suggesting biological associations with global relevance.

Nicotine from cigarette smoking and diet and Parkinson disease: a review

Evidence from epidemiological studies suggest a relationship between cigarette smoking and low risk of Parkinson disease (PD). As a major component of tobacco smoke, nicotine has been proposed to be a substance for preventing against PD risk, with a key role in regulating striatal activity and behaviors mediated through the dopaminergic system. Animal studies also showed that nicotine could modulate dopamine transmission and reduce levodopa-induced dyskinesias. However, previous clinical trials yield controversial results regarding nicotine treatment. In this review, we updated epidemiological, preclinical and clinical data, and studies on nicotine from diet. We also reviewed interactions between genetic factors and cigarette smoking. As a small amount of nicotine can saturate a substantial portion of nicotine receptors in the brain, nicotine from other sources, such as diet, could be a promising therapeutic substance for protection against PD.

Projection of the prevalence of Parkinson's disease in the coming decades: Revisited

OBJECTIVE

Previous studies have estimated future PD prevalence based on population aging. This study revisits that projection by accounting for the potential impact of declining rates of smoking.

METHODS

The age- and gender-stratified smoking prevalence in the United States from 2000 to 2040 were obtained from the U.S. Census Bureau and the U.S. Surgeon General's Smoking Report. PD prevalence was estimated based on population aging with and without an account of the impact of declining smoking rates. Relative risks of 0.56 and 0.78 were applied for current and former smokers, respectively.

RESULTS

Accounting for aging alone, ∼700,000 PD cases are predicted by 2040. After accounting for the declining smoking prevalence, ∼770,000 cases, an increase of ∼10% over the estimate without smoking, is predicted.

CONCLUSIONS

If the epidemiological association of smoking and PD is causal, projecting future cases without considering smoking may underestimate disease burden, underscoring the urgency of adequate resource allocation. © 2017 International Parkinson and Movement Disorder Society.

Tobacco Use, Oral Health, and Risk of Parkinson's Disease

Few studies have investigated the associations between use of Swedish moist snuff (snus), associated poor oral health, and risk of Parkinson's disease (PD). We followed 20,175 participants who were free of PD in 1973-1974 in Uppsala, Sweden, until the end of 2012. We used Cox proportional hazards regression models to estimate hazard ratios and corresponding 95% confidence intervals for the associations between tobacco use, oral health indicators, and PD risk. We found that tobacco use was associated with a lower risk of PD in males. Compared with males who never used any tobacco daily, pure ever tobacco smokers, pure ever snus users, and combined users had adjusted hazard ratios of 0.68 (95% confidence interval (CI): 0.49, 0.93; n = 83), 0.51 (95% CI: 0.27, 0.95; n = 11), and 0.21 (95% CI: 0.07, 0.67; n = 3), respectively. No association was observed for number of teeth, dental plaque, or detectable oral mucosal lesions and PD risk, although there was a suggestive association with Candida-related oral mucosal lesions in males (hazard ratio = 1.56, 95% CI: 0.92, 2.65; P = 0.098). Use of snus is associated with a lower risk of PD in males, while poor oral health seems not to be associated with PD occurrence.

Idiopathic REM sleep behavior disorder and neurodegenerative risk: To tell or not to tell to the patient? How to minimize the risk?

Most people with idiopathic REM sleep behavior disorder (iRBD) have an underlying synucleinopathy, mainly Parkinson's disease (PD) or dementia with Lewy bodies, with median conversion time of 4-9 y from iRBD diagnosis and of 11-16 y from symptom onset. Subtle signs and imaging tests indicate concomitant neurodegeneration in widespread brain areas. Risk factor studies suggest that iRBD patients may have prior head injury, occupational farming, pesticide exposure, low education level and possibly more frequent family history of dream-enactment behavior (but not of PD), plus unexpected risk factors (smoking, ischemic heart disease and inhaled corticosteroid use). Unlike PD, caffeine and smoking appear not to have a protective role. Prior depression and antidepressant use may be early neurodegenerative signs rather than exclusively causative factors. Age, hyposmia, impaired color vision, abnormal dopaminergic imaging, mild cognitive impairment and possibly sleepiness, may identify patients at greater risk of more rapid conversion. The consensus is to generally disclose the neurodegenerative risk to patients (with the caveat that phenoconversion and its temporal course remain uncertain in individuals without "soft neurodegenerative signs" and those under 50 y of age), to suggest a healthy lifestyle and to take part in prospective cohort studies in anticipation of eventual neuroprotective trials.

Traffic-related air pollution increased the risk of Parkinson's disease in Taiwan: A nationwide study

BACKGROUND

Ambient air pollution has been associated with many health conditions, but little is known about its effects on neurodegenerative diseases, such as Parkinson's disease (PD). In this study, we investigated the influence of ambient air pollution on PD in a nationwide population-based case-control study in Taiwan.

METHODS

We identified 11,117 incident PD patients between 2007 and 2009 from the Taiwanese National Health Insurance Research Database and selected 44,468 age- and gender-matched population controls from the longitudinal health insurance database. The average ambient pollutant exposure concentrations from 1998 through the onset of PD were estimated using quantile-based Bayesian Maximum Entropy models. Basing from logistic regression models, we estimated the odds ratios (ORs) and 95% confidence intervals (CIs) of ambient pollutant exposures and PD risk.

RESULTS

We observed positive associations between NO_x, CO exposures, and PD. In multi-pollutant models, for NO_x and CO above the 75th percentile exposure compared with the lowest percentile, the ORs of PD were 1.37 (95% CI=1.23-1.52) and 1.17 (95% CI=1.07-1.27), respectively.

CONCLUSIONS

This study suggests that ambient air pollution exposure, especially from traffic-related pollutants such as NO_x and CO, increases PD risk in the Taiwanese population.

Increased epigenetic age and granulocyte counts in the blood of Parkinson's disease patients

It has been a long standing hypothesis that blood tissue of PD Parkinson's disease (PD) patients may exhibit signs of accelerated aging. Here we use DNA methylation based biomarkers of aging (“epigenetic clock”) to assess the aging rate of blood in two ethnically distinct case-control data sets. Using n=508 Caucasian and n=84 Hispanic blood samples, we assess a) the intrinsic epigenetic age acceleration of blood (IEAA), which is independent of blood cell counts, and b) the extrinsic epigenetic age acceleration rate of blood (EEAA) which is associated with age dependent changes in blood cell counts. Blood of PD subjects exhibits increased age acceleration according to both IEAA (p=0.019) and EEAA (p=6.1×10⁻³). We find striking differences in imputed blood cell counts between PD cases and controls. Compared to control subjects, PD subjects contains more granulocytes (p=1.0×10⁻⁹ in Caucasians, p=0.00066 in Hispanics) but fewer T helper cells (p=1.4×10⁻⁶ in Caucasians, p=0.0024 in Hispanics) and fewer B cells (p=1.6×10⁻⁵ in Caucasians, p=4.5×10⁻⁵ in Hispanics). Overall, this study shows that the epigenetic age of the immune system is significantly increased in PD patients and that granulocytes play a significant role.

The epidemiology of Parkinson's disease: risk factors and prevention

Since 2006, several longitudinal studies have assessed environmental or behavioural factors that seem to modify the risk of developing Parkinson's disease. Increased risk of Parkinson's disease has been associated with exposure to pesticides, consumption of dairy products, history of melanoma, and traumatic brain injury, whereas a reduced risk has been reported in association with smoking, caffeine consumption, higher serum urate concentrations, physical activity, and use of ibuprofen and other common medications. Randomised trials are investigating the possibility that some of the negative risk factors might be neuroprotective and thus beneficial in individuals with early Parkinson's disease, particularly with respect to smoking (nicotine), caffeine, and urate. In the future, it might be possible to identify Parkinson's disease in its prodromal phase and to promote neuroprotective interventions before the onset of motor symptoms. At this time, however, the only intervention that seems justifiable for the primary prevention of Parkinson's disease is the promotion of physical activity, which is likely to be beneficial for the prevention of several chronic diseases.

Non-Motor Correlates of Smoking Habits in de Novo Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) subjects are less likely to ever smoke and are more prone to quit smoking, as compared to controls. Therefore, smoking habits can be considered part of the non-motor phenotype, preceding the onset of motor PD by several years.

OBJECTIVE

To explore non-motor symptom (NMS) correlates of smoking habits in de novo PD.

METHODS

This cross-sectional study included 281 newly diagnosed, drug-naïve PD subjects, recruited in Naples (Italy) and in Kassel (Germany). All subjects completed the NMS Questionnaire (NMSQ), and were investigated for smoking status (never, current and former smokers) and intensity (pack-years).

RESULTS

140 PD subjects never smoked, 20 currently smoked, and 121 had quit smoking before PD diagnosis. NMSQ total score did not associate with smoking status, but with smoking intensity (p = 0.028; coefficient = 0.088). A multinomial logistic regression stepwise model presenting never smoking as reference, selected as NMSQ correlates of current smoking: sex difficulties (p = 0.002; OR = 5.254), daytime sleepiness (p = 0.046; OR = 0.085), insomnia (p = 0.025; OR = 0.135), and vivid dreams (p = 0.040; OR = 3.110); and of former smoking: swallowing (p = 0.013; OR = 0.311), nausea (p = 0.027; OR = 7.157), unexplained pains (p = 0.002; OR = 3.409), forgetfulness (p = 0.005; OR = 2.592), sex interest (p = 0.007; OR = 0.221), sex difficulties (p = 0.038; OR = 4.215), and daytime sleepiness (p = 0.05; OR = 0.372). An ordinal logistic regression stepwise model selected as NMSQ correlates of smoking intensity: nocturnal restlessness (p = 0.027; coefficient = 0.974), and leg swelling (p = 0.004; coefficient = 1.305).

CONCLUSIONS

Certain NMSs are associated with different smoking status and intensity, suggesting a variety of adaptive mechanisms to cigarette smoking.

The Concept of Prodromal Parkinson's Disease

Parkinson’s disease (PD) is currently clinically defined by a set of cardinal motor features centred on the presence of bradykinesia and at least one additional motor symptom out of tremor, rigidity or postural instability. However, converging evidence from clinical, neuropathological, and imaging research suggests initiation of PD-specific pathology prior to appearance of these classical motor signs. This latent phase of neurodegeneration in PD is of particular relevance in relation to the development of disease-modifying or neuroprotective therapies which would require intervention at the earliest stages of disease. A key challenge in PD research, therefore, is to identify and validate markers for the preclinical and prodromal stages of the illness. Currently, several nonmotor symptoms have been associated with an increased risk to develop PD in otherwise healthy individuals and ongoing research is aimed at validating a variety of candidate PD biomarkers based on imaging, genetic, proteomic, or metabolomic signatures, supplemented by work on tissue markers accessible to minimally invasive biopsies. In fact, the recently defined MDS research criteria for prodromal PD have included combinations of risk and prodromal markers allowing to define target populations of future disease modification trials.

Epidemiology of Parkinson Disease

Parkinson disease (PD) is a common progressive neurodegenerative condition, causing both motor and non motor symptoms. Motor symptoms include stiffness, slowness, rest tremor and poor postural reflexes, whereas nonmotor symptoms include abnormalities of mood, cognition, sleep and autonomic function. Affected patients show cell loss in the substantia nigra pars compacta, and accumulation of aggregated alpha-synuclein into intracellular structures called Lewy bodies, within specific brain regions. The main known non modifiable risk factor is age. The neuroepidemiology of PD is complex with susceptibility genes and a number of modifiable risk factors that can increase and others that can mitigate risk and outcome.

Prodromal symptoms of Parkinson's disease: Implications for epidemiological studies of disease etiology

In recent years, there has been a major shift in our understanding of the course of Parkinson's disease (PD) from a disease of the brain to a disease of long latency, characterized by the progressive emergence of multiple non-motor symptoms, including hyposmia, constipation, depression, anxiety, rapid eye movement (REM) sleep behavior disorder and excessive daytime sleepiness, as well as subtle motor signs, before the typical motor signs appear. Epidemiological studies have made major contributions by allowing better characterization of subsequent PD risk in relation to non-motor symptoms. Such findings have profound implications for the conduct of epidemiological studies examining risk and protective factors in PD, and the interpretation of their findings. Given the length of the prodromal period, reverse causation in particular is a major concern with many reported associations. One striking feature of PD etiology, compared with other diseases, is the presence of numerous inverse associations. If these associations are truly causal, they would have major implications for disease prevention and for slowing disease progression. However, whether these associations are truly causal remains to be demonstrated in future studies. Experimental studies play an important role by offering a better understanding of the underlying mechanisms. Well-designed epidemiological studies using innovative approaches will also be key in elucidating whether these intriguing associations are causal or a consequence of reverse causation.

Linking Smoking, Coffee, Urate, and Parkinson's Disease - A Role for Gut Microbiota?

While the etiology and pathogenesis of Parkinson's disease (PD) is still obscure, there is evidence for lifestyle factors influencing disease risk. Best established are the inverse associations with smoking and coffee consumption. In other contexts there is evidence that health effects of lifestyle factors may depend on gut microbiome composition. Considering the gastrointestinal involvement in PD, it was recently speculated, that the associations between smoking, coffee, and PD risk could be mediated by gut microbiota. Here we review such a possible mediatory role of gut microbiota taking into account recent findings on microbiome composition in PD and extending the scope also to urate.

Cautionary optimism: caffeine and Parkinson's disease risk

Most Parkinson’s disease (PD) patients present without known family history and without a diagnosed prodromal phase, underscoring the difficulty of employing primary (neuroprevention) and secondary (neuroprotection) preventions. In cases of monogenic forms, however, potential gene-carrying family members of a proband could engage in neuroprevention, such as exercise or diet modifications, to attenuate the risk of, or delay, disease development. However, a historical lack of recognized disease-modifying interventions has limited clinicians’ ability to recommend reliable preventive measures in caring for at-risk populations. We briefly analyze the first retrospective study to examine caffeine consumption and PD risk in a LRRK2 R1628P cohort.

Association between Parkinson's Disease and Cigarette Smoking, Rural Living, Well-Water Consumption, Farming and Pesticide Use: Systematic Review and Meta-Analysis

Objective

Bradford Hill’s viewpoints were used to conduct a weight-of-the-evidence assessment of the association between Parkinson’s disease (PD) and rural living, farming and pesticide use. The results were compared with an assessment based upon meta-analysis. For comparison, we also evaluated the association between PD and cigarette smoking as a “positive control” because a strong inverse association has been described consistently in the literature.

Methods

PubMed was searched systematically to identify all published epidemiological studies that evaluated associations between Parkinson’s disease (PD) and cigarette smoking, rural living, well-water consumption, farming and the use of pesticides, herbicides, insecticides, fungicides or paraquat. Studies were categorized into two study quality groups (Tier 1 or Tier 2); data were abstracted and a forest plot of relative risks (RRs) was developed for each risk factor. In addition, when available, RRs were tabulated for more highly exposed individuals compared with the unexposed. Summary RRs for each risk factor were calculated by meta-analysis of Tier 1, Tier 2 and all studies combined, with sensitivity analyses stratified by other study characteristics. Indices of between-study heterogeneity and evidence of reporting bias were assessed. Bradford Hill’s viewpoints were used to determine if a causal relationship between PD and each risk factor was supported by the weight of the evidence.

Findings

There was a consistent inverse (negative) association between current cigarette smoking and PD risk. In contrast, associations between PD and rural living, well-water consumption, farming and the use of pesticides, herbicides, insecticides, fungicides or paraquat were less consistent when assessed quantitatively or qualitatively.

Conclusion

The weight of the evidence and meta-analysis support the conclusion that there is a causal relationship between PD risk and cigarette smoking, or some unknown factor correlated with cigarette smoking. There may be risk factors associated with rural living, farming, pesticide use or well-water consumption that are causally related to PD, but the studies to date have not identified such factors. To overcome the limitations of research in this area, future studies will have to better characterize the onset of PD and its relationship to rural living, farming and exposure to pesticides.

Adjustment disorder and risk of Parkinson's disease

BACKGROUND AND PURPOSE

It has been postulated that stress is part of the etiological process of Parkinson's disease (PD). The risk of PD was examined in a cohort of patients with adjustment disorders, a diagnosis made in the presence of a severe response to a stressful life event.

METHODS

Using Danish medical registries, PD occurrence was examined in a nationwide population-based cohort of patients with adjustment disorder diagnosed between 1995 and 2011. The standardized incidence ratio of PD was calculated as the ratio of observed to expected cases, stratified by time and potential risk factors, including depression and anxiety.

RESULTS

Our adjustment disorder cohort (67 786 patients) was followed for a median of 8 years (interquartile range 4, 12.6 years). During follow-up, 119 patients developed PD, versus 64 expected, corresponding to a standardized incidence ratio of 1.84 (95% confidence interval 1.53, 2.20). Consistent results were observed after stratification on potential risk factors, including depression and anxiety.

CONCLUSION

Adjustment disorder, a diagnosis made in the presence of severe response to stressful life events, was associated with an increased risk of PD.