Effects of ulcerative colitis and Crohn’s disease on neurodegenerative diseases: A Mendelian randomization study

Amyloid, Crohn's disease, and Alzheimer's disease - are they linked?

Crohn's disease (CD) is a chronic inflammatory disease that most frequently affects part of the distal ileum, but it may affect any part of the gastrointestinal tract. CD may also be related to systemic inflammation and extraintestinal manifestations. Alzheimer's disease (AD) is the most common neurodegenerative disease, gradually worsening behavioral and cognitive functions. Despite the meaningful progress, both diseases are still incurable and have a not fully explained, heterogeneous pathomechanism that includes immunological, microbiological, genetic, and environmental factors. Recently, emerging evidence indicates that chronic inflammatory condition corresponds to an increased risk of neurodegenerative diseases, and intestinal inflammation, including CD, increases the risk of AD. Even though it is now known that CD increases the risk of AD, the exact pathways connecting these two seemingly unrelated diseases remain still unclear. One of the key postulates is the gut-brain axis. There is increasing evidence that the gut microbiota with its proteins, DNA, and metabolites influence several processes related to the etiology of AD, including β-amyloid abnormality, Tau phosphorylation, and neuroinflammation. Considering the role of microbiota in both CD and AD pathology, in this review, we want to shed light on bacterial amyloids and their potential to influence cerebral amyloid aggregation and neuroinflammation and provide an overview of the current literature on amyloids as a potential linker between AD and CD.

Association between inflammatory bowel disease and all-cause dementia: A two-sample Mendelian randomization study

BACKGROUND

Numerous observational studies have documented a correlation between inflammatory bowel disease (IBD) and an increased risk of dementia. However, the causality of their associations remains elusive.

AIM

To assess the causal relationship between IBD and the occurrence of all-cause dementia using the two-sample Mendelian randomization (MR) method.

METHODS

Genetic variants extracted from the large genome-wide association study (GWAS) for IBD (the International IBD Genetics Consortium, n = 34652) were used to identify the causal link between IBD and dementia (FinnGen, n = 306102). The results of the study were validated via another IBD GWAS (United Kingdom Biobank, n = 463372). Moreover, MR egger intercept, MR pleiotropy residual sum and outlier, and Cochran's Q test were employed to evaluate pleiotropy and heterogeneity. Finally, multiple MR methods were performed to estimate the effects of genetically predicted IBD on dementia, with the inverse variance wei-ghted approach adopted as the primary analysis.

RESULTS

The results of the pleiotropy and heterogeneity tests revealed an absence of significant pleiotropic effects or heterogeneity across all genetic variants in outcome GWAS. No evidence of a causal effect between IBD and the risk of dementia was identified in the inverse variance weighted [odds ratio (OR) = 0.980, 95%CI : 0.942-1.020, P value = 0.325], weighted median (OR = 0.964, 95%CI : 0.914-1.017, P value = 0.180), and MR-Egger (OR = 0.963, 95%CI : 0.867-1.070, P value = 0.492) approaches. Consistent results were observed in validation analyses. Reverse MR analysis also showed no effect of dementia on the development of IBD. Furthermore, MR analysis suggested that IBD and its subtypes did not causally affect all-cause dementia and its four subtypes, including dementia in Alzheimer's disease, vascular dementia, dementia in other diseases classified elsewhere, and unspecified dementia.

CONCLUSION

Taken together, our MR study signaled that IBD and its subentities were not genetically associated with all-cause dementia or its subtypes. Further large prospective studies are warranted to elucidate the impact of intestinal inflammation on the development of dementia.

Association between inflammatory bowel disease and Parkinson's disease: a prospective cohort study of 468,556 UK biobank participants

Introduction

Inflammatory Bowel Disease (IBD) and Parkinson's disease (PD) are both chronic, progressive disorders. As such, given the inconclusive results of extensive research on the association between IBD and PD, our study intends to examine this relationship further using the UK Biobank database.

Methods

We conducted a prospective cohort study using the Cox proportional hazards model, analyzing data from the UK Biobank to investigate the relationship between IBD and PD, following subjects until PD diagnosis, loss to follow up, death or study termination on 30 June, 2023.

Results

The results show that IBD had no effect on the risk of PD (HR: 1.356, 95% CI: 0.941-1.955, p = 0.103), and the effect remained consistent in specific Crohn's disease, ulcerative colitis or unclassified IBD populations. In addition, after sensitivity analysis using propensity matching scores and excluding patients diagnosed with PD 5 or 10 years after baseline, IBD had no effect on the risk of PD. However, in the subgroup analysis, we found that in females (HR: 1.989, 95% CI: 1.032-3.835, p = 0.040), the polygenic risk score was highest (HR: 2.476, 95% CI: 1.401-4.374, p = 0.002), and having ulcerative colitis without hypertension (HR: 2.042, 95% CI: 1.128-3.697, p = 0.018) was associated with an increased risk of PD.

Conclusion

In conclusion, over an average follow-up period of 13.93 years, we found no significant association between IBD and PD.

Inflammation, Autoimmunity and Neurodegenerative Diseases, Therapeutics and Beyond

Neurodegenerative disease (ND) incidence has recently increased due to improved life expectancy. Alzheimer's (AD) or Parkinson's disease (PD) are the most prevalent NDs. Both diseases are poly genetic, multifactorial and heterogenous. Preventive medicine, a healthy diet, exercise, and controlling comorbidities may delay the onset. After the diseases are diagnosed, therapy is needed to slow progression. Recent studies show that local, peripheral and age-related inflammation accelerates NDs' onset and progression. Patients with autoimmune disorders like inflammatory bowel disease (IBD) could be at higher risk of developing AD or PD. However, no increase in ND incidence has been reported if the patients are adequately diagnosed and treated. Autoantibodies against abnormal tau, β amyloid and α- synuclein have been encountered in AD and PD and may be protective. This discovery led to the proposal of immune-based therapies for AD and PD involving monoclonal antibodies, immunization/ vaccines, pro-inflammatory cytokine inhibition and anti-inflammatory cytokine addition. All the different approaches have been analysed here. Future perspectives on new therapeutic strategies for both disorders are concisely examined.

Effects of heart failure and coronary artery disease on erectile dysfunction: a two-sample mendelian randomization study

BACKGROUND AND AIMS

There are no clear conclusions as to whether heart failure (HF) and coronary heart disease (CAD) increase the risk of erectile dysfunction (ED).In our study, we used Mendelian randomization (MR) analysis to discover a causal relationship between HF, CAD and ED.

METHODS

Single nucleotide polymorphisms (SNPs) associated with HF, CAD and ED were obtained from the MRC IEU Open Genome-Wide Association Study (GWAS) database.After a series of screenings, the remaining SNPs were selected as instrumental variables (IVs) for HF and CAD for MR analysis to assess the relationship between genetically predicted HF or CAD and the pathogenesis of ED.Among them, we used the random-effects inverse variance weighted (IVW) method as the primary analysis method.Finally, Cochran's q-test, funnel plots, MR-Egger regression, Leave-one-out method and MR-PRESSO were used for sensitivity analysis.

RESULTS

In the IVW method, there was no significant causal relationship between genetically predicted HF and CAD and the incidence of ED.(HF: OR = 1.17, 95% CI 0.99-1.39; p = 0.074;CAD: OR = 1.08, 95% CI 0.99-1.17, p = 0.068)。The results of sensitivity analyses supported our conclusion that no horizontal pleiotropism was found.

CONCLUSION

This study did not find a causal relationship between HF or CAD and ED in European populations, which requires further in-depth research.

Lack of Causal Associations of Inflammatory Bowel Disease with Parkinson's Disease and Other Neurodegenerative Disorders

BACKGROUND

Observational studies have indicated associations between inflammatory bowel disease (IBD) and neurodegenerative diseases, including Parkinson's disease (PD).

OBJECTIVE

To evaluate the causal associations of IBD with PD and other selected neurodegenerative disorders using updated data.

METHODS

Bidirectional two-sample Mendelian randomization studies using genome-wide association studies summary statistics of IBD and PD.

RESULTS

We found a lack of evidence for the causal association of IBD on PD (odds ratio [OR], 1.014; 95% confidence interval [CI], 0.967-1.063; P = 0.573). Reverse analysis also indicated no evidence of a causal effect for PD on IBD (OR, 0.978; 95% CI, 0.910-1.052; P = 0.549). The causality between IBD and Alzheimer's disease, amyotrophic lateral sclerosis, and multiple sclerosis was unfounded (all P > 0.05).

CONCLUSIONS

The updated analyses provide no clear evidence for causal associations of IBD with PD or the other three neurodegenerative diseases. Potential confounders might contribute to the previously observed associations, and further investigations are warranted. © 2023 International Parkinson and Movement Disorder Society.

Effects of major depression and bipolar disorder on erectile dysfunction: a two-sample mendelian randomization study

BACKGROUND AND AIMS

There are currently no clear conclusions about whether major depression (MD) and bipolar disorder (BD) increase the risk of erectile dysfunction (ED). In our study, we used a Mendelian randomization (MR) analysis to discover the causal associations between MD, BD and ED.

METHODS

We got single-nucleotide polymorphisms (SNPs) related to MD, BD and ED from the MRC IEU Open genome-wide association study (GWAS) datasets. After a series of selection, SNPs left were selected as instrumental variables (IVs) of MD and BD for the following MR test to evaluate the relationship of genetically predicted MD or BD with the incidence of ED. Among them, we used the random-effects inverse-variance weighted (IVW) method as the main analysis. Finally, sensitivity analyses were further performed using Cochran's Q test, funnel plots, MR-Egger regression, Leave-one-out method and MR- pleiotropy residual sum and outlier (PRESSO).

RESULTS

Genetically-predicted MD was causally related to the incidence of ED in the IVW methods (odds ratio (OR), 1.53; 95% confidence interval (CI), 1.19-1.96; p = 0.001), while no causal impact of BD on the risk of ED (OR = 0.95, 95% CI 0.87-1.04; p = 0.306). The results of sensitivity analyses supported our conclusion, and no directional pleiotropy were found.

CONCLUSION

The findings of this research found evidence of a causal relationship between MD and ED. However, we did not find a causal relationship between BD and ED in European populations.

Genetic overlap between Parkinson's disease and inflammatory bowel disease

Parkinson's disease and inflammatory bowel disease have been increasingly associated, implying shared pathophysiology. To explore biological explanations for the reported connection, we leveraged summary statistics of updated genome-wide association studies and characterized the genetic overlap between the two diseases. Aggregated genetic association data were available for 37 688 cases versus 981 372 controls for Parkinson's disease and 25 042 cases versus 34 915 controls for inflammatory bowel disease. Genetic correlation was estimated with the high-definition likelihood method. Genetic variants with joint association to both diseases were identified by conditional false discovery rate framework and further annotated to reveal shared loci, genes, and enriched pathways. For both Crohn's disease and ulcerative colitis, the two main subtypes of inflammatory bowel disease, we detected weak but statistically significant genetic correlations with Parkinson's disease (Crohn's disease: r_g = 0.06, P = 0.01; ulcerative colitis: r_g = 0.06, P = 0.03). A total of 1290 variants in 27 independent genomic loci were detected to associate with Parkinson's disease and Crohn's disease at conjunctional false discovery rate under 0.01 and 1359 variants in 15 loci were pleiotropic to Parkinson's disease and ulcerative colitis. Among the identified pleiotropic loci, 23 are novel and have never been associated with both phenotypes. A mixture of loci conferring either same or opposing genetic effects on two phenotypes was also observed. Positional and expression quantitative trait loci mapping prioritized 296 and 253 genes for Parkinson's disease with Crohn's disease and ulcerative colitis, respectively, among which only <10% are differentially expressed in both colon and substantia nigra. These genes were identified to overrepresent in pathways regulating gene expression and post-translational modification beyond several immune-related pathways enriched by major histocompatibility complex genes. In conclusion, we found robust evidence for a genetic link between Parkinson's disease and inflammatory bowel disease. The identified genetic overlap is complex at the locus and gene levels, indicating the presence of both synergistic and antagonistic pleiotropy. At the functional level, our findings implied a role of immune-centered mechanisms in the reported gut-brain connection.

Inflammatory bowel disease and risk of Parkinson's disease: evidence from a meta-analysis of 14 studies involving more than 13.4 million individuals

Background

The relationship between inflammatory bowel disease (IBD) and the risk of Parkinson's Disease (PD) has been investigated in several epidemiological studies. However, the results of these studies were inconclusive and inconsistent. We evaluated the potential relationship between IBD and PD risk by a meta-analysis.

Methods

Search the electronic databases PubMed, Embase and Cochrane databases from inception to November 30, 2022, to identify relevant studies that assess the risk of PD in patients with IBD. The cohort, cross-sectional, mendelian randomization and case-control studies that reported risk estimates of PD and IBD were included in our analysis. The random-effect model and fixed-effects model were used to calculate the summary relative risks (RRs) with 95% confidence intervals (CIs).

Results

In total, 14 studies (nine cohort studies, two cross-sectional studies, two mendelian randomization studies and one case-control study) involving more than 13.4 million individuals were analyzed in our analysis. Our results suggested that the risk of PD in IBD patients is moderately increased, with the pooled RR was 1.17 (95% CI: 1.03-1.33, P = 0.019). Omit of any single study from this analysis had little effect on the combined risk estimate. No evidence of publication bias was found. In the subgroup analysis, the combined RR was 1.04 (95% CI: 0.96, 1.12, P = 0.311) for Crohn's disease (CD), and 1.18 (95% CI: 1.06, 1.31, P = 0.002) for ulcerative colitis (UC). In addition, a significant association was identified in patients with IBD aged ≥ 60 years (RR = 1.22; 95% CI: 1.06-1.41, P = 0.007), but not in age < 60 years (RR = 1.19; 95% CI: 0.58-2.41, P = 0.639). Meanwhile, the meta-analysis results suggested a protective role for IBD medication use against PD development, with the RR was 0.88 (95% CI: 0.74, 1.04, P = 0.126).

Conclusion

Our results indicated that patients with IBD had a moderately higher risk of PD compared to non-IBD individuals. Patients with IBD should be aware of the potential risks for PD, especially who were ≥ 60 years old.

Investigating Causality and Shared Genetic Architecture between Neurodegenerative Disorders and Inflammatory Bowel Disease

Published observational studies have revealed the connection between neurodegenerative disorders and inflammatory bowel disease (IBD), whereas the causal association remains largely unclear. Our study aims to assess the causality and identify the shared genetic architecture between neurodegenerative disorders and IBD. Two-sample Mendelian randomization analyses were performed to assess the causality between IBD and neurodegenerative disorders (amyotrophic lateral sclerosis [ALS], Alzheimer's disease [AD], Parkinson's disease [PD], and multiple sclerosis [MS]). Shared genetic loci, functional interpretation, and transcriptomic profiles were further investigated in ALS and IBD. We identified that genetic predisposition to IBD was suggestively associated with lower odds of ALS (odds ratio [OR] 0.96, 95% confidence interval [CI] 0.94 to 0.99). In contrast, IBD was not genetically associated with an increased risk of AD, PD, or MS (and vice versa). Two shared genetic loci (rs6571361 and rs7154847) were derived, and SCFD1, G2E3, and HEATR5A were further identified as novel risk genes with enriched functions related to membrane trafficking. G2E3 was differentially expressed and significantly correlated with SCFD1 in patients with ALS or IBD. Our study reveals the suggestively protective role of IBD on ALS, and does not support the causality of AD, PD, or MS on IBD (and vice versa). Our findings indicate possible shared genetic architecture and pathways between ALS and IBD. These results provide insights into the pathogenesis and therapeutics of IBD and neurodegenerative disorders.