Mendelian randomization study shows no causal relationship between circulating urate levels and Parkinson's disease

Uric acid and alterations of purine recycling disorders in Parkinson's disease: a cross-sectional study

The relationship between reduced serum uric acid (UA) levels and Parkinson's disease (PD), particularly purine metabolic pathways, is not fully understood. Our study compared serum and cerebrospinal fluid (CSF) levels of inosine, hypoxanthine, xanthine, and UA in PD patients and healthy controls. We analyzed 132 samples (serum, 45 PD, and 29 age- and sex-matched healthy controls; CSF, 39 PD, and 19 age- and sex-matched healthy controls) using liquid chromatography-tandem mass spectrometry. Results showed significantly lower serum and CSF UA levels in PD patients than in controls (p < 0.0001; effect size r = 0.5007 in serum, p = 0.0046; r = 0.3720 in CSF). Decreased serum hypoxanthine levels were observed (p = 0.0002; r = 0.4338) in PD patients compared to controls with decreased CSF inosine and hypoxanthine levels (p < 0.0001, r = 0.5396: p = 0.0276, r = 0.2893). A general linear model analysis indicated that the reduced UA levels were mainly due to external factors such as sex and weight in serum and age and weight in CSF unrelated to the purine metabolic pathway. Our findings highlight that decreased UA levels in PD are influenced by factors beyond purine metabolism, including external factors such as sex, weight, and age, emphasizing the need for further research into the underlying mechanisms and potential therapeutic approaches.

No causal relationship between serum urate and neurodegenerative diseases: A Mendelian randomization study

OBJECTIVE

Observational studies have shown that increased serum urate is associated with a lower risk of neurodegenerative diseases (NDs), but the causality remains unclear. We employed a two-sample Mendelian randomization (MR) approach to assess the causal relationship between serum urate and four common subtypes of NDs, including Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS).

METHODS

Serum urate data came from the CKDGen Consortium. GWAS data for PD, AD, ALS, and MS were obtained from four databases in the primary analysis and then acquired statistics from the FinnGen consortium for replication and meta-analysis. Inverse variance weighted (IVW), weighted median (WM), and MR-Egger regression methods were applied in the MR analyses. Pleiotropic effects, heterogeneity, and leave-one-out analyses were evaluated to validate the results.

RESULTS

There was no evidence for the effect of serum urate on PD (OR: 1.00, 95 % CI: 0.90-1.11, P = 0.97), AD (OR: 1.02, 95 % CI: 1.00-1.04, P = 0.06), ALS (OR: 1.05, 95 % CI: 0.97-1.13, P = 0.22), and MS (OR: 1.01, 95 % CI: 0.89-1.14, P = 0.90) risk when combined with the FinnGen consortium, neither was any evidence of pleiotropy detected between the instrumental variables (IVs).

CONCLUSION

The MR analysis suggested that serum urate may not be causally associated with a risk of PD, AD, ALS, and MS.

Update: Protective and risk factors for Parkinson disease

We review the epidemiologic literature on potential protective and risk factors in Parkinson's Disease (PD). Prior research identified numerous possible protective and risk factors. Potential protective factors include tobacco abuse, physical activity, urate levels, NSAID use, calcium channel blocker use, statin use, and use of some α1-adrenergic antagonists. Some potential protective factors could be products of reverse causation, including increased serum urate, tobacco abuse, and coffee-tea-caffeine consumption. Potential risk factors include traumatic brain injury, pesticide exposure, organic solvent exposure, lead exposure, air pollution, Type 2 Diabetes, some dairy products, cardiovascular disease, and some infections including Hepatitis C, H. pylori, and COVID-19. Potential non-environmental risk factors include bipolar disorder, essential tremor, bullous pemphigoid, and inflammatory bowel disease. There is an inverse relationship with PD and risk of most cancers. Though many potential protective and risk factors for PD were identified, research has not yet led to unique, rigorous prevention trials or successful disease-modifying interventions. While efforts to reduce exposure to some industrial toxicants are well justified, PD incidence might be most effectively reduced by mitigation of risks, such as Type 2 Diabetes, air pollution, traumatic brain injury, or physical inactivity, that are general public health intervention targets.

Use of Mendelian randomization to assess the causal status of modifiable exposures for rheumatic diseases

The explosion in Mendelian randomization (MR) publications is hard to ignore and shows no signs of slowing. Clinician readers, who may not be familiar with jargon-ridden methods, are expected to discern the good from the many low-quality studies that make overconfident claims of causality or stretch the plausibility of what MR can investigate. We aim to equip readers with foundational concepts, contextualized using examples in rheumatology, to appraise the many MR papers that are or will appear in their journals. We highlight the importance of assessing whether exposures are under plausibly specific genetic influence, whether the hypothesized causal pathways make biological sense, and whether results stand up to replication and use of control outcomes. Quality of research can vary substantially using MR as with any design, and all methods have inherent limitations. MR studies have provided and can still contribute valuable insights in the context of evidence triangulation.

Serum urate levels and neurodegenerative outcomes: a prospective cohort study and mendelian randomization analysis of the UK Biobank

BACKGROUND

Previous studies on the associations between serum urate levels and neurodegenerative outcomes have yielded inconclusive results, and the causality remains unclear. This study aimed to investigate whether urate levels are associated with the risks of Alzheimer's disease and related dementias (ADRD), Parkinson's disease (PD), and neurodegenerative deaths.

METHODS

This prospective study included 382,182 participants (45.7% men) from the UK Biobank cohort. Cox proportional hazards models were used to assess the associations between urate levels and risk of neurodegenerative outcomes. In the Mendelian randomization (MR) analysis, urate-related single-nucleotide polymorphisms were identified through a genome-wide association study. Both linear and non-linear MR approaches were utilized to investigate the potential causal associations.

RESULTS

During a median follow-up period of 12 years, we documented 5,400 ADRD cases, 2,553 PD cases, and 1,531 neurodegenerative deaths. Observational data revealed that a higher urate level was associated with a decreased risk of ADRD (hazard ratio [HR]: 0.93, 95% confidence interval [CI]: 0.90, 0.96), PD (HR: 0.87, 95% CI: 0.82, 0.91), and neurodegenerative death (HR: 0.88, 95% CI: 0.83, 0.94). Negative linear associations between urate levels and neurodegenerative events were observed (all P-values for overall < 0.001 and all P-values for non-linearity > 0.05). However, MR analyses yielded no evidence of either linear or non-linear associations between genetically predicted urate levels and the risk of the aforementioned neurodegenerative events.

CONCLUSION

Although the prospective cohort study demonstrated that elevated urate levels were associated with a reduced risk of neurodegenerative outcomes, MR analyses found no evidence of causality.

Mendelian Randomization Applied to Neurology: Promises and Challenges

The Mendelian randomization (MR) paradigm allows for causal inferences to be drawn using genetic data. In recent years, the expansion of well-powered publicly available genetic association data related to phenotypes such as brain tissue gene expression, brain imaging, and neurologic diseases offers exciting opportunities for the application of MR in the field of neurology. In this review, we discuss the basic principles of MR, its myriad applications to research in neurology, and potential pitfalls of injudicious applications. Throughout, we provide examples where MR-informed findings have shed light on long-standing epidemiologic controversies, provided insights into the pathophysiology of neurologic conditions, prioritized drug targets, and informed drug repurposing opportunities. With the ever-expanding availability of genome-wide association data, we project MR to become a key driver of progress in the field of neurology. It is therefore paramount that academics and clinicians within the field are familiar with the approach.

A Mendelian randomization study of serum uric acid with the risk of venous thromboembolism

BACKGROUND

Observational studies have linked hyperuricemia with venous thromboembolism (VTE). We aimed to investigate whether there are causal relationships between uric acid levels and VTE and its subtypes, including deep venous thrombosis (DVT) of the lower extremities and pulmonary embolism (PE).

METHODS

We utilized Mendelian randomization (MR) analysis to estimate the causal association in European individuals. We extracted two sets of polygenic instruments strongly associated (p < 5 × 10^-8) with uric acid from the CKDGen consortium and UK biobank, respectively. Genetic associations with the risk of VTE, DVT, and PE were obtained from the FinnGen biobank. We used the inverse-variance weighted method as the preliminary estimate. Additionally, we employed MR-Egger, weighted median, and Mendelian randomization pleiotropy residual sum and outlier method as complementary assessments. Sensitivity analyses were performed to test for pleiotropic bias.

RESULTS

The genetically instrumented serum uric acid levels had no causal effects on VTE, DVT, and PE. Two sets of polygenic instruments used for exposure, along with three complementary MR methods, also yielded no significant association.

CONCLUSIONS

Our MR analysis provided no compelling evidence for a causal relationship of serum uric acid with the risk of VTE. This suggests that uric acid-lowering therapies in patients with hyperuricemia may not be effective in reducing the likelihood of developing VTE.

Longitudinal follow-up study of the association with gout and Alzheimer's disease and Parkinson's disease in Korea

To date, no clear conclusion on the relationships of gout with the occurrence of typical neurodegenerative diseases, Alzheimer's disease (AD) and Parkinson's disease (PD), has been reached. This study aimed to determine whether the patients with gout are at a lower or higher probability of developing AD or PD than those without gout. Longitudinal follow-up data of a representative sample of Korean adults were assessed. 18,079 individuals diagnosed with gout between 2003 and 2015 were enrolled in the gout group. The comparison group comprised 72,316 demographics-matched individuals not diagnosed with gout. Longitudinal associations of gout with AD or PD were estimated using Cox proportional hazard regression adjusting for potential confounders. The adjusted hazard ratios (HRs) of AD and PD in the gout group were 1.01 and 1.16 times higher than controls, but these differences were not statistically significant (95% confidence interval [CI] = 0.92-1.12 and 95% CI = 0.97-1.38, respectively). Although there was no significant association in the entire sample, AD and PD probabilities in patients with gout were significantly higher in participants < 60 years, and PD probabilities in patients with gout were significantly higher in overweight participants. Our findings identify significant correlations of gout with AD and PD in participants < 60 years and gout with PD in those with overweight, indicating that gout may play a role in the development of neurodegenerative diseases in younger or overweight populations. Further investigations should be performed to corroborate these findings.

Disease-modifying vs symptomatic treatments: Splitting over lumping

Clinical trials of putative disease-modifying therapies in neurodegeneration have obeyed the century-old principle of convergence, or lumping, whereby any feature of a clinicopathologic disease entity is considered relevant to most of those affected. While this convergent approach has resulted in important successes in trials of symptomatic therapies, largely aimed at correcting common neurotransmitter deficiencies (e.g., cholinergic deficiency in Alzheimer's disease or dopaminergic deficiency in Parkinson's disease), it has been consistently futile in trials of neuroprotective or disease-modifying interventions. As individuals affected by the same neurodegenerative disorder do not share the same biological drivers, splitting such disease into small molecular/biological subtypes, to match people to therapies most likely to benefit them, is vital in the pursuit of disease modification. We here discuss three paths toward the splitting needed for future successes in precision medicine: (1) encourage the development of aging cohorts agnostic to phenotype in order to enact a biology-to-phenotype direction of biomarker development and validate divergence biomarkers (present in some, absent in most); (2) demand bioassay-based recruitment of subjects into disease-modifying trials of putative neuroprotective interventions in order to match the right therapies to the right recipients; and (3) evaluate promising epidemiologic leads of presumed pathogenetic potential using Mendelian randomization studies before designing the corresponding clinical trials. The reconfiguration of disease-modifying efforts for patients with neurodegenerative disorders will require a paradigm shift from lumping to splitting and from proteinopathy to proteinopenia.

Dual role of brain-derived extracellular vesicles in dementia-related neurodegenerative disorders: cargo of disease spreading signals and diagnostic-therapeutic molecules

Neurodegenerative disorders are one of the most common causes of disability and represent 6.3% of the global burden of disease. Among them, Alzheimer's, Parkinson's, and Huntington's diseases cause cognitive decline, representing the most disabling symptom on both personal and social levels. The molecular mechanisms underlying the onset and progression of dementia are still poorly understood, and include secretory factors potentially affecting differentiated neurons, glial cells and neural stem cell niche. In the last decade, much attention has been devoted to exosomes as novel carriers of information exchanged among both neighbouring and distant cells. These vesicles can be generated and internalized by different brain cells including neurons, neural stem cells, astrocytes, and microglia, thereby affecting neural plasticity and cognitive functions in physiological and pathological conditions. Here, we review data on the roles of exosomes as carriers of bioactive molecules potentially involved in the pathogenesis of neurodegenerative disorders and detectable in biological fluids as biomarkers of dementia. We also discuss the experimental evidence of the therapeutic potential of stem cell-derived vesicles in experimental models of neurodegeneration-dependent cognitive decline.

Uric Acid in Parkinson's Disease: What Is the Connection?

Numerous studies have linked Parkinson's disease (PD) with low levels of uric acid (UA). Low UA has been associated with the risk of developing PD, and its progression and severity. The biological mechanisms underlying these relationships have never been firmly established. The most frequently proposed mechanism is that UA is an antioxidant. Low UA is thought to predispose to oxidative stress, which contributes to dopamine neuron degeneration, and leads to initial appearance of symptoms of PD and its worsening over time. Several recent studies have questioned this explanation. In this review, we describe the biology of UA, its many links with PD, evidence regarding UA as an antioxidant, and we question whether UA causes PD or contributes to its progression. We also address the possibility that something about PD causes low UA (reverse causation) or that low UA is a biomarker of some other more relevant mechanism in PD. We hope the evidence provided here will stimulate additional studies to better understand the links between UA and PD. Elucidating these mechanisms remains important, because they may provide new insights into the pathogenesis of PD or novel approaches to treatments. © 2022 International Parkinson and Movement Disorder Society.

Systematic review of Mendelian randomization studies on Parkinson's disease

Background

Parkinson's disease (PD) is known to be associated with non-genetic factors. To infer causality, Mendelian randomization (MR) studies are increasingly used. Here, genetic variants are used as instrumental variables for the risk factor but have no direct effect on PD themselves.

Methods

We performed a systematic literature review on MR studies for PD. Studies were identified searching the PubMed database. Upon data extraction, we evaluated the methodological quality and summarized the evidence.

Results

Twelve articles were included. Most studies showed "good" methodological quality, but most did not report proper power estimations. Twelve analyses yielded nominally significant effects.

Conclusions

Our systematic review shows that most MR studies were well performed and allow to identify causal exposures, which may inform further studies on the prevention and early intervention of PD.

Dairy Intake and Parkinson's Disease: A Mendelian Randomization Study

BACKGROUND

Previous prospective studies highlighted dairy intake as a risk factor for Parkinson's disease (PD), particularly in men. It is unclear whether this association is causal or explained by reverse causation or confounding.

OBJECTIVE

The aim is to examine the association between genetically predicted dairy intake and PD using two-sample Mendelian randomization (MR).

METHODS

We genotyped a well-established instrumental variable for dairy intake located in the lactase gene (rs4988235) within the Courage-PD consortium (23 studies; 9823 patients and 8376 controls of European ancestry).

RESULTS

Based on a dominant model, there was an association between genetic predisposition toward higher dairy intake and PD (odds ratio [OR] per one serving per day = 1.70, 95% confidence interval = 1.12-2.60, P = 0.013) that was restricted to men (OR = 2.50 [1.37-4.56], P = 0.003; P-difference with women = 0.029).

CONCLUSIONS

Using MR, our findings provide further support for a causal relationship between dairy intake and higher PD risk, not biased by confounding or reverse causation. Further studies are needed to elucidate the underlying mechanisms. © 2022 International Parkinson and Movement Disorder Society.

The Promise of Mendelian Randomization in Parkinson's Disease: Has the Smoke Cleared Yet for Smoking and Parkinson's Disease Risk?

This commentary discusses the strengths and limitations of utilizing the Mendelian randomization (MR) approach in Parkinson's disease (PD) studies. Epidemiologists proposed to employ MR when genetic instruments are available that represent reliable proxies for modifiable lifelong exposures which elude easy measurement in studies of late onset diseases like PD. Here, we are using smoking as an example. The great promise of the MR approach is its resilience to confounding and reverse causation. Nevertheless, the approach has some drawbacks such as being liable to selection- and survival-bias, it makes some strong assumptions about the genetic instruments employed, and requires very large sample sizes. When interpreted carefully and put into the context of other studies that take both genetics and the environment into consideration, MR studies help us to not only ask interesting questions but also can support causal inference and provide novel insights.

Hyperuricemia, Gout, and the Brain-an Update

PURPOSE OF REVIEW

This review aims to summarize recent evidence regarding the complex relationship between uric acid (UA), gout, and brain diseases.

RECENT FINDINGS

Observational studies have suggested that patients with hyperuricemia or gout might have a decreased risk of neurodegenerative diseases. Conversely, they may be at increased risk of cerebrovascular disease. Mendelian randomization (MR) studies use a genetic score as an instrumental variable to address the causality of the association between a risk factor (here, UA or gout) and an outcome. So far, MR analyses do not support a causal relationship of UA or gout with Alzheimer's disease and dementia, and of UA with Parkinson's disease or stroke. Observation studies indicate a U-shaped association between UA and brain diseases, but MR studies do not support that this association is causal. Further studies should address the causal role of gout as well as the impact of urate-lowering therapy on these outcomes.

Cognition, motor symptoms, and glycolipid metabolism in Parkinson's disease with depressive symptoms

Depressive symptoms and abnormal glycolipid metabolisms are common in patients with Parkinson's disease (PD), but their relationship has not been fully reported. It is not clear whether glycolipid impairments lead to poor cognitive and motor function, and aggravate depressive symptoms. Therefore, we aimed to explore the relationships between glycolipid variables, cognition, motor and depressive symptoms in PD patients cross-sectionally. Two hundred ten PD patients were recruited. Glycolipid parameters and Uric acid (UA) were measured. Depressive symptoms, cognitive function and motor symptoms were assessed using the Hamilton Depression Rating Scale-17 (HAMD-17), the Montreal Cognitive Assessment (MOCA) and the Movement Disorder Society Unified Parkinson's Disease Rating Scale Part-III (UPDRS-III). Depressive PD patients had significantly worse motor symptoms and higher levels of fasting plasma glucose (FPG) than those in non-depressive patients (F = 24.145, P < 0.001). Further, logistic regression analysis indicated that UPDRS-III (OR = 1.039, 95% CI 1.019-1.057, P = 0.044), FPG (OR = 1.447, 95% CI 1.050-1.994, P = 0.024) were independently associated with depression. In PD patients without depression, UA (β = - 0.068, t = - 2.913, P = 0.005) and cholesterol (CHOL) (β = - 3.941, t = - 2.518, P = 0.014) were independent predictors of the UPDRS-III score; in addition, UPDRS-III score was negatively associated with MOCA score (β = - 0.092, t = - 2.791, P = 0.007). FPG levels and motor symptoms were related to depressive symptoms in PD patients. Further, in non-depressive PD patients, UA and CHOL showed putative biomarkers of motor symptoms.

Effect of Urate-Elevating Inosine on Early Parkinson Disease Progression: The SURE-PD3 Randomized Clinical Trial

Importance

Urate elevation, despite associations with crystallopathic, cardiovascular, and metabolic disorders, has been pursued as a potential disease-modifying strategy for Parkinson disease (PD) based on convergent biological, epidemiological, and clinical data.

Objective

To determine whether sustained urate-elevating treatment with the urate precursor inosine slows early PD progression.

Design, Participants, and Setting

Randomized, double-blind, placebo-controlled, phase 3 trial of oral inosine treatment in early PD. A total of 587 individuals consented, and 298 with PD not yet requiring dopaminergic medication, striatal dopamine transporter deficiency, and serum urate below the population median concentration (<5.8 mg/dL) were randomized between August 2016 and December 2017 at 58 US sites, and were followed up through June 2019.

Interventions

Inosine, dosed by blinded titration to increase serum urate concentrations to 7.1-8.0 mg/dL (n = 149) or matching placebo (n = 149) for up to 2 years.

Main Outcomes and Measures

The primary outcome was rate of change in the Movement Disorder Society Unified Parkinson Disease Rating Scale (MDS-UPDRS; parts I-III) total score (range, 0-236; higher scores indicate greater disability; minimum clinically important difference of 6.3 points) prior to dopaminergic drug therapy initiation. Secondary outcomes included serum urate to measure target engagement, adverse events to measure safety, and 29 efficacy measures of disability, quality of life, cognition, mood, autonomic function, and striatal dopamine transporter binding as a biomarker of neuronal integrity.

Results

Based on a prespecified interim futility analysis, the study closed early, with 273 (92%) of the randomized participants (49% women; mean age, 63 years) completing the study. Clinical progression rates were not significantly different between participants randomized to inosine (MDS-UPDRS score, 11.1 [95% CI, 9.7-12.6] points per year) and placebo (MDS-UPDRS score, 9.9 [95% CI, 8.4-11.3] points per year; difference, 1.26 [95% CI, -0.59 to 3.11] points per year; P = .18). Sustained elevation of serum urate by 2.03 mg/dL (from a baseline level of 4.6 mg/dL; 44% increase) occurred in the inosine group vs a 0.01-mg/dL change in serum urate in the placebo group (difference, 2.02 mg/dL [95% CI, 1.85-2.19 mg/dL]; P<.001). There were no significant differences for secondary efficacy outcomes including dopamine transporter binding loss. Participants randomized to inosine, compared with placebo, experienced fewer serious adverse events (7.4 vs 13.1 per 100 patient-years) but more kidney stones (7.0 vs 1.4 stones per 100 patient-years).

Conclusions and Relevance

Among patients recently diagnosed as having PD, treatment with inosine, compared with placebo, did not result in a significant difference in the rate of clinical disease progression. The findings do not support the use of inosine as a treatment for early PD.

Trial Registration

ClinicalTrials.gov Identifier: NCT02642393.

Parkinson disease risks: correctly identifying environmental factors for a chronic disease

Parkinson disease (PD) is now the world's fastest growing brain disease; however, the factors underlying this rise are unclear. The past 25 years has witnessed a vast expansion in our understanding of the genetics of PD, but few individuals with PD carry one of the major known genetic risk factors. Environmental factors, including individual (e.g., medications) and ambient (e.g., pollutants), may contribute to this rise. In this issue of the JCI, Sasane et al. examined the risk of PD associated with medications commonly used to treat benign prostatic hypertrophy. In contrast with previous studies, certain α1 receptor antagonists failed to lower PD risk. Rather, the commonly used comparator drug, tamsulosin, increased PD risk. This finding highlights the importance of selecting comparator groups to correctly identify risk factors. Future studies to address the rise of PD with emphasis on both individual as well as the understudied ambient environmental factors are warranted.

Mendelian Randomisation Finds No Causal Association between Urate and Parkinson's Disease Progression

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative movement disorder. Observational studies suggest higher levels of plasma urate may protect against Parkinson's risk and progression; however, causality cannot be established.

OBJECTIVES

This study set out to determine whether there is a true causal association between urate levels and PD age at onset (AAO) and progression severity using recently released PD AAO and progression genome-wide association study (GWAS) data.

METHODS

A large two-sample Mendelian randomization design was employed, using genetic variants underlying urate levels and the latest GWAS data for PD outcomes.

RESULTS

This study found no causal association between urate levels and Parkinson's risk, AAO, or progression severity.

CONCLUSIONS

Our results predict increasing urate levels as a therapeutic strategy is unlikely to benefit PD patients. © 2021 International Parkinson and Movement Disorder Society.

Lack of Causal Effects or Genetic Correlation between Restless Legs Syndrome and Parkinson's Disease

BACKGROUND

Epidemiological studies have reported an association between Parkinson's disease (PD) and restless legs syndrome.

OBJECTIVES

We aimed to use genetic data to study whether these 2 disorders are causally linked or share genetic architecture.

METHODS

We performed two-sample Mendelian randomization and linkage disequilibrium score regression using summary statistics from recent genome-wide meta-analyses of PD and restless legs syndrome.

RESULTS

We found no evidence for a causal relationship between restless legs syndrome (as the exposure) and PD (as the outcome, inverse variance-weighted; b = -0.003, SE = 0.031, P = 0.916; F statistic = 217.5). Reverse Mendelian randomization also did not demonstrate any causal effect of PD on restless legs syndrome (inverse variance-weighted; b = -0.012, SE = 0.023, P = 0.592; F statistic = 191.7). Linkage disequilibrium score regression analysis demonstrated lack of genetic correlation between restless legs syndrome and PD (rg = -0.028, SE = 0.042, P = 0.507).

CONCLUSIONS

There was no evidence for a causal relationship or genetic correlation between restless legs syndrome and PD. The associations observed in epidemiological studies could be attributed, in part, to confounding or nongenetic determinants. © 2021 International Parkinson and Movement Disorder Society.

Genetically predicted serum urate levels have no causal role on depression or other psychiatric disorders

Clinicians are advised caution in reducing serum urate for gout management due to observational associations with risk of neuropsychiatric diseases. We examined the causal effect of genetically predicted serum urate levels on the risk of major depressive disorder (MDD), anxiety, and related psychiatric disorders using two-sample Mendelian randomization (MR). We identified single-nucleotide polymorphisms (SNPs) associated with serum urate from a genome-wide association study (GWAS) of 110,347 European-descent individuals. The causal effect of serum urate on MDD was tested using summary data from a GWAS of 135,458 cases and 344,901 controls of European descent. MR was performed using random-effects inverse variance-weighted method and a series of sensitivity analyses. This approach was repeated using summary GWAS data for anxiety, bipolar disorder, post-traumatic stress disorder, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, schizophrenia, and anorexia nervosa. We identified 30 SNPs associated with serum urate. Genetically predicted urate levels were not causally associated with risk of MDD (OR 0.98; 95% CI 0.94, 1.03), anxiety (OR 0.90; 95% CI 0.80, 1.02), or the other psychiatric conditions (OR range 0.95 to 1.06). Results were similar in sensitivity analyses. We found no evidence that genetically predicted serum urate has a causal effect on risk of MDD, anxiety, or other psychiatric disorders. Key Points • Clinicians are advised to be cautious about reducing the serum urate level too far in gout management, citing observational associations between low serum urate levels and various neuropsychiatric diseases. • In this two-sample Mendelian randomization study, we found no evidence for a causal link between genetically predicted serum urate level and the development of major depressive, anxiety, or other related psychiatric disorders. • Future revisions of clinical guidelines may need to reconsider recommendations regarding lower limits for serum urate levels.

Mendelian randomization study shows no causal effects of serum urate levels on the risk of MS

Objective

To examine whether lifelong genetically increased serum urate levels, a potent antioxidant, contribute to MS susceptibility using Mendelian randomization (MR).

Methods

This 2-sample MR study included 25 independent genetic variants strongly associated with serum urate levels in a genome-wide association study meta-analysis of 140,949 individuals. Effects on the risk of MS were assessed with summary statistics from 3 large-scale MS genetic data sets totaling 61,667 MS cases and 86,806 controls from the International MS Genetic Consortium. Multiple sensitivity analyses were performed to evaluate the assumptions of MR and remove potentially pleiotropic variants.

Results

Using inverse-variance weighted MR, we found no evidence for a causal effect of serum urate level on the risk of MS in any of the cohorts (MS1: OR 0.99 per each mg/dL unit increase in urate, 95% CI 0.89–1.08, p = 0.76; MS2: OR = 0.99, 95% CI 0.89–1.11, p = 0.90; MS3: OR = 1.00, 95% CI 0.98–1.2, p = 0.91). Pleiotropy robust MR methods yielded consistent estimates.

Conclusion

This MR study does not support a clinically relevant causal effect of serum urate levels on the risk of MS.

Prevalence and associated factors of hyperuricemia among urban adults aged 35-79 years in southwestern China: a community-based cross-sectional study

Hyperuricemia is prevalent throughout the world. However, a well-designed large-scale epidemiological investigation of hyperuricemia in southwestern China is lacking. A regional representative sample of 10,141 participants were included using multistage, stratified sampling in Chengdu and Chongqing from September 2013 to March 2014. Hyperuricemia was defined as the self-reported of the doctor's diagnosis of hyperuricemia, or serum uric acid > 420 μmol/L in men or serum uric acid > 360 μmol/L in women. The overall age- and sex-standardized prevalence of hyperuricemia among adults aged 35-79 years was 13.5%. Compared with women, the prevalence of hyperuricemia in men was higher (17.3% versus 10.0%). Hypertension, hyperlipidemia, overweight or obesity, central obesity were associated with an increased risk for hyperuricemia both in men and in women. Married men and women were not susceptible to hyperuricemia. Current cigarette smoking was an associated risk factor of hyperuricemia only in women. Hyperuricemia has become a major health problem among urban adults aged 35-79 years in southwestern China, and special attention should be paid to men. Comorbidities associated with hyperuricemia and causality worth further investigation.

Milk and Fermented Milk Intake and Parkinson's Disease: Cohort Study

Milk and fermented milk consumption has been linked to health and mortality but the association with Parkinson’s disease (PD) is uncertain. We conducted a study to investigate whether milk and fermented milk intakes are associated with incident PD. This cohort study included 81,915 Swedish adults (with a mean age of 62 years) who completed a questionnaire, including questions about milk and fermented milk (soured milk and yogurt) intake, in 1997. PD cases were identified through linkage with the Swedish National Patient and Cause of Death Registers. Multivariable-adjusted hazard ratios were obtained from Cox proportional hazards regression models. During a mean follow-up of 14.9 years, 1251 PD cases were identified in the cohort. Compared with no or low milk consumption (<40 mL/day), the hazard ratios of PD across quintiles of milk intake were 1.29 (95% CI 1.07, 1.56) for 40–159 mL/day, 1.19 (95% CI 0.99, 1.42) for 160–200 mL/day, 1.29 (95% CI 1.08, 1.53) for 201–400 mL/day, and 1.14 (95% CI 0.93, 1.40) for >400 mL/day. Fermented milk intake was not associated with PD. We found a weak association between milk intake and increased risk of PD but no dose–response relationship. Fermented milk intake was not associated with increased risk of PD.

2020 recommendations from the French Society of Rheumatology for the management of gout: Urate-lowering therapy

OBJECTIVE

To develop French Society of Rheumatology-endorsed recommendations for the management of urate-lowering therapy (ULT).

METHODS

Evidence-based recommendations were developed by 9 rheumatologists (academic or community-based), 3 general practitioners, 1 cardiologist, 1 nephrologist and 1 patient, using a systematic literature search, one physical meeting to draft recommendations and two Delphi rounds to finalize them.

RESULTS

A set of 3 overarching principles and 5 recommendations was elaborated. The overarching principles emphasize the importance of patient education, especially the need for explaining the objective of lowering serum urate (SU) level to obtain crystal dissolution, clinical symptoms disappearance and avoidance of complications. ULT is indicated as soon as the diagnosis of gout is established. SU level must be decreased below 300μmol/l (50mg/l) in all gout patients or at least below 360μmol/l (60ml/l) when the 300μmol/l target cannot be reached, and must be maintained at these targets and monitored life-long. The choice of the ULT primarily relies on renal function: in patients whose estimated glomerular filtration rate (eGFR) is above 60ml/min/1.73m², first-line ULT is allopurinol; in those with eGFR between 30 and 60ml/min/1.73m², allopurinol use must be cautious and febuxostat can be considered as an alternative; and in those whose eGFR is below 30ml/min/1.73m², allopurinol must be avoided and febuxostat should be preferred. Prophylaxis of ULT-induced gout flares involves progressive increase of ULT dosage and low-dose colchicine for at least 6 months. Cardiovascular risk factors and diseases, the metabolic syndrome and chronic kidney disease must be screened and managed.

CONCLUSION

These recommendations aim to provide simple and clear guidance for the management of ULT in France.

Genetics of Parkinson's disease: An introspection of its journey towards precision medicine

A substantial proportion of risk for Parkinson's disease (PD) is driven by genetics. Progress in understanding the genetic basis of PD has been significant. So far, highly-penetrant rare genetic alterations in SNCA, LRRK2, VPS35, PRKN, PINK1, DJ-1 and GBA have been linked with typical familial PD and common genetic variability at 90 loci have been linked to risk for PD. In this review, we outline the journey thus far of PD genetics, highlighting how significant advances have improved our knowledge of the genetic basis of PD risk, onset and progression. Despite remarkable progress, our field has yet to unravel how genetic risk variants disrupt biological pathways and molecular networks underlying the pathobiology of the disease. We highlight that currently identified genetic risk factors only represent a fraction of the likely genetic risk for PD. Identifying the remaining genetic risk will require us to diversify our efforts, performing genetic studies across different ancestral groups. This work will inform us on the varied genetic basis of disease across populations and also aid in fine mapping discovered loci. If we are able to take this course, we foresee that genetic discoveries in PD will directly influence our ability to predict disease and aid in defining etiological subtypes, critical steps for the implementation of precision medicine for PD.

Using Mendelian randomization to understand and develop treatments for neurodegenerative disease

Common neurodegenerative diseases are thought to arise from a combination of environmental and genetic exposures. Mendelian randomization is a powerful way to leverage existing genetic data to investigate causal relationships between risk factors and disease. In recent years, Mendelian randomization has gathered considerable traction in neurodegenerative disease research, providing valuable insights into the aetiology of these conditions. This review aims to evaluate the impact of Mendelian randomization studies on translational medicine for neurodegenerative diseases, highlighting the advances made and challenges faced. We will first describe the fundamental principles and limitations of Mendelian randomization and then discuss the lessons from Mendelian randomization studies of environmental risk factors for neurodegeneration. We will illustrate how Mendelian randomization projects have used novel resources to study molecular pathways of neurodegenerative disease and discuss the emerging role of Mendelian randomization in drug development. Finally, we will conclude with our view of the future of Mendelian randomization in these conditions, underscoring unanswered questions in this field.

Serum Uric Acid, Serum Uric Acid to Serum Creatinine Ratio and Serum Bilirubin in Patients With Parkinson's Disease: A Case-Control Study

Background

Studies have shown that a low serum uric acid (SUA) level associates with Parkinson’s disease (PD), but many of them did not exclude patients with impaired renal function. Studies on the association between serum bilirubin level and PD also are limited. This study determined the association between SUA level, SUA/serum creatinine (SCr) ratio and serum bilirubin levels in PD patients with normal renal and liver functions.

Methods

The PD patients from a neurological clinic, and the controls from the club for the elderly, were recruited into this study. The PD stage and motor and non-motor function were determined by the Hoehn-Yahr (H&Y) scale and unified Parkinson’s disease rating scale (UPDRS), respectively.

Results

Sixty-one PD patients and 135 controls participated. The SUA/SCr ratio, but not SUA, was significantly lower in the PD patients than in the controls (4.12 ± 0.90 vs. 4.59 ± 1.04, P = 0.003). Serum total bilirubin (TB) and indirect bilirubin (IDB) were significantly higher in the PD patients (7.92 ± 3.67 µmol/L vs. 6.59 ± 2.78 µmol/L, P = 0.003 and 4.52 ± 2.48 µmol/L vs. 3.26 ± 1.82 µmol/L, P < 0.001), respectively. Serum TB and IDB, but not SUA or SUA/SCr ratio, were associated negatively with PD stages (P = 0.010 and P = 0.014, respectively). There was no association between TB, IDB, SUA or SUA/SCr ratio and PD disease duration or motor subtypes. No significant correlation was found between SUA or SUA/SCr ratio, serum TB and IDB.

Conclusion

The SUA/SCr ratio is more sensitive than SUA in determining their association with PD. The high serum TB and IDB levels in PD patients compared with the controls suggest that serum bilirubin might play a role in the pathogenesis of PD. However, the lack of association between SUA or the SUA/SCr ratio and serum TB or IDB suggests that these two biomarkers play a different role in the etiopathogenesis of PD.

Ten Years of the International Parkinson Disease Genomics Consortium: Progress and Next Steps

In June 2009 a small group of investigators met at the annual Movement Disorders Society meeting in Paris. The explicit goal of this meeting was to discuss a potential research alliance focused on the genetics of Parkinson disease (PD). The outcome of this informal meeting was the creation of the International Parkinson Disease Genomics Consortium (IPDGC), a group focused on collaborative genetics research, enabled by trust, sharing, and as little paperwork as possible. The IPDGC has grown considerably since its inception, including over 100 scientists from around the World. The focus has also grown, to include clinical and functional investigation of PD at scale. Most recently, the IPDGC has expanded to initiate major research efforts in East Asia and Africa, and has prioritized collaborations with ongoing major efforts in India and South America. Here we summarize the efforts of the IPDGC thus far and place these in the context of a decade of progress in PD genomics. We also discuss the future direction of IPDGC and our stated research priorities for the next decade.

Plasma urate concentrations and possible REM sleep behavior disorder

Objective

To examine how urate concentrations are related to the risk of having possible REM sleep behavior disorder (pRBD) in a community‐based cohort.

Methods

The study included 12,923 Chinese adults of the Kailuan Study, free of Parkinson disease (PD) and dementia. Plasma urate concentrations were measured in 2006, 2008, and 2010. Cumulative average urate concentration was used as primary exposure. In 2012, we determined pRBD status using a validated RBD questionnaire‐Hong Kong (RBDQ‐HK). Logistic regression analysis was performed to estimate the association between urate concentrations during 2006–2010 and odds of having pRBD in 2012 or pRBD case with symptom onset within 1 year.

Results

Higher average urate concentrations were associated with a lower odds of pRBD (P‐trend <0.001). The adjusted odds ratio (OR), for the highest versus lowest urate quintiles, was 0.43 (95% confidence intervals (CIs) 0.32–0.57). Significant association was consistently observed when we examined the association of a single urate assessment (2006 or 2010) or the rate of change in urate concentrations during 2006–2010 with pRBD (P‐trend <0.001 for all). However, restricting to pRBD onset during 2011–2012, we observed a nonsignificant trend between high urate concentration and high odds of pRBD (P‐trend = 0.09).

Interpretation

Higher average urate concentrations were associated with a lower likelihood of having pRBD, but not new‐onset pRBD. Because of its observational study design, the result should be interpreted with caution due to the possibility of residual confounding.

Gene-environment interaction and Mendelian randomisation

Genetic factors only account for up to a third of the cases of Parkinson's disease (PD), while the remaining cases are of unknown aetiology. Environmental exposures (such as pesticides or heavy metals) and the interaction with genetic susceptibility factors (summarized in the concept of impaired xenobiotic metabolism) are believed to play a major role in the mechanisms of neurodegeneration. Beside of the classical association studies (e.g. genome-wide association studies), a novel approach to investigate environmental risk factors are Mendelian randomisation studies. This review explores the gene-environment interaction and the gain of Mendelian randomisation studies in assessing causalities of modifiable risk factors for PD.

Risky behaviors and Parkinson disease: A mendelian randomization study

Objective

To examine causal associations between risky behavior phenotypes and Parkinson disease using a mendelian randomization approach.

Methods

We used 2-sample mendelian randomization to generate unconfounded estimates using summary statistics from 2 independent, large meta-analyses of genome-wide association studies on risk-taking behaviors (n = 370,771–939,908) and Parkinson disease (cases n = 9,581, controls n = 33,245). We used the inverse variance weighted method as the main method for judging causality.

Results

Our results support a strong protective association between the tendency to smoke and Parkinson disease (odds ratio [OR] 0.714 per log odds of ever smoking, 95% confidence interval [CI] 0.568–0.897, p = 0.0041, Cochran Q test p = 0.238; I² index 6.3%). Furthermore, we observed risk association trends between automobile speed propensity and the number of sexual partners and Parkinson disease after removal of overlapping loci with other risky traits (OR 1.986 for each 1-SD increase in normalized automobile speed propensity, 95% CI 1.215–3.243, p = 0.0066; OR 1.635 for each 1-SD increase in number of sexual partners, 95% CI 1.165–2.293, p = 0.0049).

Conclusion

These findings provide support for a causal relationship between general risk tolerance and Parkinson disease and may provide new insights into the pathogenic mechanisms leading to the development of Parkinson disease.

Role of cigarette smoking in the development of ischemic stroke and its subtypes: a Mendelian randomization study

Purpose

Numerous studies have indicated that smokers have an increased risk of developing ischemic stroke. However, less is known about the causal relationship between cigarette smoking and ischemic stroke subtypes. In the present study, we aim to determine whether genetically predicted cigarette smoking was associated with subtypes of ischemic stroke using Mendelian randomization (MR).

Patients and methods

We used summary-level genetic association data from the MEGASTROKE consortium, including 438,847 individuals of European ancestry (34,217 cases of ischemic stroke and 404,630 controls). We used 176 single nucleotide polymorphisms as instrumental variables, which were previously identified to be associated with smoking in the Study of the Social Science Genetic Association Consortium (n=518,633). MR analyses were performed using inverse-variance-weighted method, weighted-median method, and MR-Egger regression.

Results

We found that genetically predicted smoking was associated with a higher risk of ischemic stroke (odds ratio (OR): 1.24, 95% CI: 1.10–1.39) and large artery ischemic stroke (OR: 1.52, 95% CI: 1.14–2.02), but not with risk of cardioembolic ischemic stroke or small vessel ischemic stroke. Sensitivity analyses using alternative MR approaches produced similar results.

Conclusion

Genetic predisposition toward smoking is causally associated with a higher incidence of large artery ischemic stroke. Further work is warranted to clarify the underlying mechanism of smoking in the development of large artery ischemic stroke.

Lipids, Apolipoproteins, and the Risk of Parkinson Disease

RATIONALE

A complete picture of the associations of the most common lipid fractions, including total cholesterol (TC), LDL-C (low-density lipoprotein cholesterol), HDL-C (high-density lipoprotein cholesterol), triglycerides, and apolipoproteins, with the risk of Parkinson disease (PD), is lacking.

OBJECTIVE

To assess the associations of lipids and apolipoproteins with the future risk of PD.

METHODS AND RESULTS

In the AMORIS (Apolipoprotein-Related Mortality Risk) Study, we enrolled ≈600 000 participants during 1985 to 1996 in Stockholm, Sweden, with repeated measurements of TC, LDL-C, HDL-C, triglycerides, ApoB (apolipoprotein B), and ApoA-I (apolipoprotein A-I). The cohort was followed until the end of 2011, and incident cases of PD were identified through the Swedish Patient Register. We first used Cox models to estimate the associations of these biomarkers with later risk of PD. We further applied a Mendelian randomization analysis for TC, LDL-C, and triglycerides using the GWAS (Genome-wide association study) summary statistics from the public PD GWAS data and 23andMe PD cohorts with >800 000 individuals. One SD increase of TC was associated with a lower hazard of PD (hazard ratio, 0.90; 95% CI, 0.87-0.94). Similar associations were observed for LDL-C (hazard ratio, 0.93; 95% CI, 0.88-0.98), triglycerides (hazard ratio, 0.94; 95% CI, 0.90-0.97), and ApoB (hazard ratio, 0.91; 95% CI, 0.85-0.97). A clear dose-response relation was also noted when using these biomarkers as categorical variables. A causal inverse association of TC, LDL-C, and triglycerides with PD risk was further suggested by the Mendelian randomization analysis.

CONCLUSIONS

Our findings reinforce that higher levels of TC, LDL-C, and triglycerides are associated with a lower future risk of PD and further suggest that these associations may be causal. The findings for ApoB in relation to PD risk are novel, and whether such association is causal needs to be examined.

Age at menarche and epithelial ovarian cancer risk: A meta-analysis and Mendelian randomization study

Age at menarche (AAM) was found to be associated with ovarian cancer risk in previous observational studies. However, the causality of this association remains unclear. Here, after systematic meta-analyses, we performed two-sample Mendelian randomization (MR) analyses to evaluate the causal effect of AAM in epithelial ovarian cancer (EOC) etiology. We performed meta-analyses including 11 410 cases and 1 163 117 noncases to quantitatively evaluate the association between AAM and ovarian cancer risk. In MR analyses, we used 25 single nucleotide polymorphisms (SNPs) associated with AAM for Chinese and 390 SNPs for Europeans as instrumental variables. MR estimates were calculated using inverse-variance weighted methods from 1044 cases and 1172 controls in a Chinese genome-wide association study and validated by the Ovarian Cancer Association Consortium and Consortium of Investigators of Modifiers of BRCA1/2 studies with 29 396 cases and 68 502 controls of European ancestry. In meta-analyses, we observed an inverse association (odds ratio [OR] = 0.96, 95% confidence interval [CI] = 0.93 to 1.00, P = 0.036) between per year older AAM and ovarian cancer risk in case-control studies, but no association was observed in cohort studies. In MR analyses, the OR of EOC risk per year increase in AAM was 0.81 (95% CI = 0.67 to 0.97, P = 0.026) in Chinese and 0.94 (95% CI = 0.90 to 0.98, P = 0.003) in Europeans, respectively. Our study supports a causal association between AAM and EOC risk.