Assessment of relationships between bullous pemphigoid and neurological diseases: A bidirectional two-sample Mendelian randomization study

Causal association between psoriasis vulgaris and bullous pemphigoid: a two-sample bidirectional Mendelian randomization study

Background

The association between psoriasis vulgaris and bullous pemphigoid (BP) remains largely unknown.

Objectives

To investigate whether there is a causal effect between psoriasis vulgaris and BP.

Methods

Two-sample bidirectional Mendelian randomization (MR) analyses were conducted using publicly released genome-wide association studies (GWAS) summary statistics. The GWAS summary statistics for BP were downloaded online from FinnGen Biobank Documentation of the R12 release, which includes 219 BP cases and 218,066 controls. The GWAS data for psoriasis vulgaris were extracted from Sakaue et al., which comprises 5072 cases and 478,102 controls. Single-nucleotide polymorphisms (SNPs) associated with exposure were selected as instrumental variables by performing additional quality control steps. The inverse-variance-weighted (IVW) method was used for the primary MR analyses, and the MR-Egger regression, weighted mode method, weighted median method, and simple mode were employed for sensitivity analyses. The MR-Egger intercept test and "leave-one-out" sensitivity analysis were performed to evaluate the horizontal pleiotropy and the potentially influential SNPs, respectively.

Results

Genetically determined log odds of psoriasis vulgaris were associated with an increased risk of BP (IVW: odds ratio (OR) = 1.263, 95% confidence interval (CI): 1.013-1.575, P=0.038). Sensitivity analyses by the weighted mode (OR=1.255, 95%CI: 0.973-1.618, P=0.106), MR Egger (OR=1.315, 95%CI: 0.951-1.817, P=0.126), simple mode (OR=1.414, 95%CI: 0.823-2.429, P=0.234) and weighted median method (OR=1.177, 95%CI: 0.889-1.559, P=0.254) derived directionally consistent relationship between the genetically predicted log odds of psoriasis vulgaris and risks of developing BP. On the contrary, we found that genetically predicted BP had no significant effect on psoriasis vulgaris (IVW: OR=0.996, P= 0.707), indicating the unidirectionality of the relationship. MR-Egger intercept tests showed no evidence of horizontal pleiotropy. No influential SNP driving the results was detected by the leave-one-out sensitivity analysis.

Conclusions

Our results suggested that psoriasis vulgaris causally increases the risk of BP, highlighting the need for potential strategies for the prevention and early diagnosis of comorbid BP in patients with psoriasis vulgaris. Further researches into this association and underlying mechanisms are warranted.

Relationship between bullous pemphigoid and malignancy: A Mendelian randomization study

Bullous pemphigoid (BP) is the most common autoimmune blistering disease, which primarily affects the elderly. However, the relationship between BP and malignancy remains controversial in traditional observational studies. The aim of this study, which included only European populations, was to assess the potential causative link between BP and 13 types of malignant tumors in a two-sample Mendelian randomization (MR) study. BP was not associated with an increased risk of developing 13 types of malignant tumors. This study did not find a causal relationship between BP and malignant tumors. However, further research is warranted to examine the generalizability of this conclusion in non-European populations.

Exploring genetic associations between vitiligo and mental disorders using Mendelian randomization

Although a large number of existing studies have confirmed that people with vitiligo are prone to mental disorders, these observational studies may be subject to confounding factors and reverse causality, so the true causal relationship is inconclusive. We conducted a bidirectional Mendelian randomization (MR) analysis to assess the causality between vitiligo and mental disorders, namely depression, anxiety, insomnia, schizophrenia, bipolar disorder, obsessive-compulsive disorder (OCD) and attention-deficit hyperactivity disorder (ADHD). Summary statistics from large available genome-wide association study (GWAS) datasets for generalized vitiligo (n = 44 266), depression (n = 173 005), anxiety (n = 17 310), insomnia (n = 386 988), schizophrenia (n = 130 644), bipolar disorder (n = 413 466), OCD (n = 9725) and ADHD (n = 225 534) were utilized. Inverse-variance weighted (IVW), MR-Egger and weighted median were employed to estimate causal effects. Sensitivity analysis and MR Pleiotropy Residual Sum and Outliers (MR PRESSO) were conducted to assess heterogeneity and pleiotropy, ensuring the robustness of the results. Additionally, we corrected for estimating bias that might be brought on by sample overlap using MRlap. In our findings, none of the rigorous bidirectional MR analyses uncovered a significant causal association. Even after applying the MRlap correction, the effect sizes remained statistically nonsignificant, thereby reinforcing the conclusions drawn via IVW. In summary, our genetic-level investigation did not reveal a causal link between generalized vitiligo and mental disorders.