Ulcerative colitis and Nephrotic syndrome: a two-sample Mendelian randomization study

doi:10.21203/rs.3.rs-4080464/v1

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Ulcerative colitis and Nephrotic syndrome: a two-sample Mendelian randomization study

https://doi.org/10.21203/rs.3.rs-4080464/v1

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Journal Publication

published 08 May, 2024

Read the published version in Internal and Emergency Medicine →

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Objectives

This study employed Mendelian randomization to investigate the potential causal relationship between ulcerative colitis and nephrotic syndrome

Methods

We obtained the whole-genome association study data of ulcerative colitis in the European population from the GWAS database. Relevant single nucleotide polymorphisms (SNPs) were selected for analysis. We employed the inverse variance-weighted meta-analysis of multiplicative random effects models to obtain SNP-specific Wald ratio estimates, which assume horizontal pleiotropy. In addition, we performed sensitivity analyses using MR-Egger, weighted median, and IVW.

Results

Our findings suggest a strong association between ulcerative colitis and nephrotic syndrome(P < 0.05). After conducting sensitivity analyses, we found no evidence of horizontal pleiotropy or heterogeneity(P > 0.05).

Conclusion

Our Mendelian randomization study provides evidence for an association between ulcerative colitis and nephrotic syndrome, which may help us better understand the conditions of ulcerative colitis and nephropathy, as well as their relationship.

Ulcerative colitis

Nephrotic syndrome

Mendelian randomization study

Ulcerative colitis is a common chronic inflammation of the colon, typically observed in adults aged 30–40. It originates from the rectum, extends to the proximal colon, and is often closely associated with defects in the intestinal epithelial barrier, microbiota, and immune responses. Patients commonly manifest with bloody diarrhea.¹ Risk factors for ulcerative colitis often include a history of Salmonella or Campylobacter infection, residing in Western industrialized countries or high-latitude regions, and a family history of the disease.² Research investigations reveal that the incidence rate of ulcerative colitis has been increasing worldwide in the 21st century. The highest prevalence areas of inflammatory bowel disease in Europe and North America have exceeded 0.3%.³ In Europe, the estimated annual treatment costs associated with ulcerative colitis range from €12.5 to €29.1 billion.⁴

Nephrotic syndrome is the third most prevalent cause of end-stage renal disease in the United States, following diabetes and hypertension. It is characterized by edema, proteinuria, hypoalbuminemia, and hyperlipidemia.⁵ The most common causes of nephrotic syndrome can be classified into primary and secondary etiologies. Primary causes often include minimal change disease (MCD), primary and secondary membranous nephropathy, and focal segmental glomerulosclerosis (FSGS). Secondary causes often include diabetes, lupus nephritis, amyloidosis, HIV, and multiple myeloma.⁶ Type 2 diabetes is the most frequently encountered secondary cause of nephrotic syndrome in most countries.⁷

As a heterogeneous disorder, inflammatory bowel disease manifests in the gastrointestinal tract and often involves other organs such as the skin, joints, biliary tract, and so on.⁸Generally speaking, the manifestations of the kidney often follow the clinical course of IBD, which may significantly impact patients' quality of life, morbidity, and mortality.⁹During ulcerative colitis, symptoms such as nephrolithiasis, glomerulonephritis, and secondary amyloidosis often occur. These symptoms can lead to nephrotic syndrome.¹⁰

Mendelian randomization (MR) typically employs genetic variations as instrumental variables (IVs) to investigate the causal relationship between observed exposure effects and outcomes.¹¹It is a method that employs the random distribution of genetic variations in nature to simulate an experimental design akin to a randomized controlled trial, grounded on the principles of Mendelian genetics.¹² With the widespread application of genome-wide association study (GWAS) databases, Mendelian randomization has attracted increasing attention and become a commonly used statistical method in modern medicine.

Two-sample Mendelian randomization analysis is a commonly used MR method that allows for MR studies using GWA databases and does not restrict the use of individual-level data from samples in MR analyses.¹³

In this study, we conducted a two-sample MR analysis using the GWAS database to investigate the relationship between ulcerative colitis and nephrotic syndrome.

MR and assumptions:

The study of us is a two-sample Mendelian randomization study which uses genetic tools [single nucleotide polymorphisms (SNPs)] to predict ulcerative colitis and NS from GWAS. Legitimate genetic instrumental variables (GIVs) must adhere to three fundamental presumptions in order to be considered legitimate ¹⁴: GIVs must (i) be intimately linked to Ulcerative colitis; (ii) solely have an impact on Ulcerative colitis in order to alter NS; and (iii) have no other confounding effects.

Data Sources:

Genetic instrumental factors were chosen based on single nucleotide polymorphisms (SNPs) connected to Ulcerative colitis. Summary statistics for Ulcerative colitis were obtained from the IEU-GWAS, involving 6,968 clinically diagnosed cases and 20,464 controls from European populations. SNPs associated with NS were also derived from the IEU-GWAS in a sample of 775 cases and 475,255 controls from East Asian. From the IEU GWAS database (https://gwas.mrcieu.ac.uk/datasets/), all datasets may be downloaded. The current research design is illustrated in Fig. 1.

Selection of genetic instruments:

We performed a set of quality control techniques to filter eligible genetic IVs that fulfill the three core MR assumptions. Firstly, we selected independent SNPs that were strongly associated with Ulcerative colitis with p-value less than 5×10 − 8. Then, to exclude SNPs that were in strong linkage disequilibrium (LD), we performed the clumping procedure with R2 < 0.001. SNP having a lower p-value would be kept among SNP pairings with an LD R2 greater than the stated threshold. We utilized these carefully chosen SNPs as the final genetic IVs for the subsequent MR analysis.

Statistical analysis:

In the analysis, we obtained SNP-specific Wald ratio estimates using inverse variance-weighted meta-analysis of multiplicative random effects models, which assume horizontal pleiotropy. Since the "exclusion-restriction" is difficult to verify, we performed sensitivity analyses under different assumptions, including MR-Egger, weighted median, and IVW methods.

We performed MR-Egger regression to assess potential directional pleiotropy driven by SNPs acting as mediated variables. The intercept term in MR-Egger regression can indicate whether directional pleiotropy is driving the MR analysis results. The MR-PRESSO analysis, it seeks to reduce heterogeneity in causal effect estimates by removing outliers that disproportionately drive heterogeneity. We used the IVW method and MR-Egger regression to detect heterogeneity, quantified by the Cochran Q statistic. A p-value < 0.05 would be considered significant heterogeneity. Additionally, to identify potentially influential SNPs, we performed a "leave-one-out" sensitivity analysis in which MR estimates are re-calculated omitting one SNP at a time.

All analyses were performed using R Version 4.3.1 with the R package ‘TwosampleMR’. We used publicly available summary data so no ethical approval is required.

The significant genetic correlations between Ulcerative colitis and nephrotic syndrome were demonstrated in our comparative analysis convincingly. Three methods known as MR Egger, WM, and IVW were used for feasibility study the causal effect of Ulcerative colitis on the nephrotic syndrome. It indicated significant associations among the three modern MR methods properly based on the remarkable consistency (MR Egger OR: 1.225, 95%CI: [1.023, 1.467], P = 0.034; WM OR: 1.150, 95%CI: [1.041, 1.271], P = 0.006; IVW OR: 1.083, 95% CI: [1.011, 1.159], P = 0.023). Table 1 provides additional information regarding the analysis mentioned.

Table 1

MR estimates of Ulcerative colitis on NS.
outcome	exposure	method	nsnp	OR	95%CL	pval
Nephrotic syndrome	Ulcerative colitis	MR Egger	37	1.225	[1.023, 1.467]	0.034
		Weighted median	37	1.15	[1.408,1.271]	0.006
		Inverse variance weighted	37	1.083	[1.011,1.159]	0.023
		Simple mode	37	1.145	[0.967,1.356]	0.126
		Weighted mode	37	1.177	[1.041,1.331]	0.013

As shown in communal Table 2, it provided more pertinent details on the relationship of heterogeneity and pleiotropy. No horizontal pleiotropy and heterogeneity can be concluded from the desired results of negative (P > 0.05) hypnotic MR-Egger regression. To make the results undoubtedly more intuitive and visible, methods about Scatter plots, Funnel patches, leave-one-out plots, and forest plots were taken as supplementary materials (Fig. 2).

Table 2

Sensitivity analyses of MR.
Outcomes	heterogeneity test						Pleiotropy test
	IVW			MR-Egger			MR-Egger intercept
	Q	Q_df	Q_pval	Q	Q_df	Q_pval	Intercept	SE	P
Ulcerative colitis	35.49	35	0.445	37.62	36	0.395	-0.0253	0.017	0.1565

Ulcerative colitis is a chronic inflammatory bowel disease, and its incidence has been increasing in recent years, especially in developing countries ¹⁵. UC primarily affects the colon and rectum, leading to the formation of ulcers on the surface of the intestinal mucosa. The main symptoms of ulcerative colitis include abdominal pain, diarrhea, and bloody stools. Other common symptoms include weight loss, fatigue, anemia, and decreased appetite. In severe cases, high fever, further weight loss, and dehydration may also occur. The exact cause of ulcerative colitis is not fully understood at present, but it is believed to be associated with various factors such as genetics, immune abnormalities, and environmental factors.

Patients with nephrotic syndrome often present with massive proteinuria, hypoalbuminemia, edema, and hyperlipidemia. NS is classified into three major types: primary, secondary, and genetic. In adults, focal segmental glomerulosclerosis and membranous nephropathy are the most common primary causes, while diabetes is the most common secondary cause. Other secondary causes include systemic lupus erythematosus and hepatitis B or C ¹⁶. Due to glomerular injury, the body shows abnormal renal filtration function. The main symptoms of NS include a significant increase in urine output during urination. Due to the presence of a large amount of protein in the urine, it appears foamy. At the same time, due to the loss of protein, the protein levels in the blood decrease, leading to hypoalbuminemia. Moreover, abnormal renal filtration function can cause fluid to accumulate abnormally in the interstitial tissues, leading to edema, especially in the legs, abdomen, and face. NS can also cause hyperlipidemia, which is an elevated level of fats (such as cholesterol and triglycerides) in the blood. The causes of NS are diverse and may include inflammatory diseases, genetic factors, immune system abnormalities, and drug reactions, among others. Common causes include minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and membranoproliferative glomerulonephritis ¹⁷.

There is a certain connection between ulcerative colitis and NS. Although they are two different diseases, ulcerative colitis can trigger NS. The incidence of NS in patients with ulcerative colitis is relatively low, but the risk still exists. While ulcerative colitis primarily affects the colon and rectum, it can also cause extraintestinal manifestations that involve almost every organ system at any stage of the clinical course of ulcerative colitis. In the past, research has considered NS as a rare extraintestinal manifestation of ulcerative colitis because it occurs together with the clinical course of ulcerative colitis ¹⁸. There have also been reports of two long-term ulcerative colitis patients developing NS. In one of the patients, renal function improved rapidly after colon resection surgery. The morphological changes observed in renal biopsy were consistent with the presence of focal segmental glomerulosclerosis ¹⁹.

The relationship between ulcerative colitis and NS may involve multiple factors. One possible factor is medication side effects. Some ulcerative colitis patients may develop NS as a side effect of the long-term use of drugs used to treat the disease, such as glucocorticoids and immunosuppressants. This includes drug-induced tubulointerstitial nephritis, histopathological changes in the kidneys, and proteinuria. Previous studies have documented cases where patients presented for a diagnosis of NS 1.5 weeks after having a 1-year history of pancolitis. They had been treated with sulfasalazine and had no previous confirmed kidney disease ²⁰.

Another factor is immune system abnormalities. Both ulcerative colitis and NS are immune-related disorders, and abnormal immune responses may lead to inflammation and pathological changes, resulting in immune-mediated glomerulonephritis and damage to the kidneys. Dysregulation of the immune system can simultaneously affect the colon and kidneys, leading to the coexistence of these two conditions. There is a link between glomerular pathologies and inflammatory bowel disease, especially with regard to the deposition of immunoglobulin A (IgA) ²¹.

In addition, ulcerative colitis patients may also experience thrombosis, which can lead to obstruction of blood flow in the renal blood vessels, resulting in the occurrence of NS. Thrombosis may be an extraintestinal manifestation, meaning that ulcerative colitis can affect the blood vessels. Studies have found that the probability of thrombosis in ulcerative colitis patients is approximately 0.44% ²².

Lastly, the inflammatory response may also be associated with the pathogenesis of both conditions. Ulcerative colitis and NS are both related to inflammatory states, and the inflammatory response may play a role in the development of these two diseases. In ulcerative colitis, intestinal inflammation can lead to the entry of inflammatory mediators and bacterial toxins into the bloodstream, affecting kidney function and leading to the occurrence of NS.

This is the first time we have used Mendelian randomization (MR) analysis to study the causal relationship between ulcerative colitis and NS. Our study has several notable strengths. Firstly, we employed a two-sample MR analysis method, which can accurately determine the direction of causality and avoid confounding and reverse causality issues, thereby enhancing the accuracy of causal inference results. Furthermore, we utilized genetic variants as instrumental variables, as genetic mutations exist before the onset of disease in individuals, thereby avoiding retrospective bias and enabling the assessment of causal relationships that are difficult to intervene in, thereby enhancing the reliability of the study. Moreover, we selected SNPs with higher F statistics, which helps to increase the statistical power of the two-sample MR analysis and reduce the risk of false-positive results. A higher F statistic indicates that the selected SNPs have stronger explanatory power for the variation of the exposure, providing more accurate and reliable genetic instrumental variables and improving the ability to detect causal relationships.

However, our study also has some limitations. Firstly, there may be unmeasured confounders. In a two-sample MR analysis, we assume that there are no unmeasured confounders influencing both the instrumental variables and the outcome. However, in reality, there may be many unknown factors that could interfere with the relationship between the instrumental variables and the outcomes. Failure to control for these unmeasured factors may result in inference errors or bias. Secondly, there may be population bias. Two-sample MR analysis requires that the study subjects belong to the same or similar population, which may limit the generalizability of the results to other populations. Genetic variation and environmental factors vary across different populations, so the consistency of the results between different ethnic groups may be limited.

In summary, our MR analysis results demonstrate a causal relationship between ulcerative colitis and NS. Further research is needed to investigate how ulcerative colitis and NS interact with each other in terms of pathophysiology.

Ethics approval and consent to participate

None.

Consent for publication

Not applicable.

Availability of data and materials

The data that support the findings of this study are available in GWAS summary data which were downloaded from https://gwas.mrcieu.ac.uk/datasets/.

Competing interests

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

None.

Authors' contributions

Jinfeng Zhan and Yujie Rao were responsible for the entire project. Jinfeng Zhan, Yujie Rao, Jiahao Liu, Haizhou Miao and Zhongbin Xia were responsible for drafting and revising the final review paper. All the authors contributed to the writing of the article and reviewed and approved the final version of the manuscript.

Acknowledgments

None.

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Journal Publication

published 08 May, 2024

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You are reading this latest preprint version

Ulcerative colitis and Nephrotic syndrome: a two-sample Mendelian randomization study

Status:

Journal Publication

Version 1

Abstract

Objectives

Methods

Results

Conclusion

Figures

Introduction

Methods

MR and assumptions:

Data Sources:

Selection of genetic instruments:

Statistical analysis:

Results

Discussion

Declarations

References

Status:

Journal Publication

Version 1