Assessment of Bidirectional Relationships between Mental Illness and Rheumatoid Arthritis: A Two-Sample Mendelian Randomization Study

Bidirectional causal relationship between psychiatric disorders and osteoarthritis: A univariate and multivariate Mendelian randomization study

BACKGROUND

Observational studies have shown associations between psychiatric disorders and osteoarthritis (OA). However, the causal impact of different psychiatric disorder types on specific sites of osteoarthritis remains unclear. This study aimed to comprehensively understand the potential causal associations between psychiatric disorders and osteoarthritis using Mendelian randomization (MR) analysis.

METHODS

We collected data from genome-wide association studies of knee osteoarthritis (KOA) (n = 403,124), hip osteoarthritis (HOA) (n = 393,873), osteoarthritis of the knee or hip (KHOA) (n = 417,596), as well as three psychiatric disorders: bipolar disorder (n = 41,917), major depressive disorder (n = 170,756), and schizophrenia (n = 76,755) among European populations. We applied bidirectional univariate and multivariate MR analyses, including inverse variance weighted, Mendelian randomization-Egger, weighted median, simple mode, and weighted mode. We considered p < .05 as a criterion for identifying potential evidence of association. Bonferroni correction was used for multiple tests.

RESULTS

Our univariate MR analysis results demonstrated that bipolar disorder is a protective factor for KOA (OR = 0.90, 95% CI = 0.83 to 0.97, p = 0.0048) and may also be protective for KHOA (p = 0.02). Conversely, major depression has a positive causal effect on both KOA (OR = 1.27; 95% CI = 1.08 to 1.49; p = 0.0036) and KHOA (OR = 1.24; 95% CI = 1.12 to 1.37; p = 3.62×10-05 ). Furthermore, our analysis suggested that KHOA may be a risk factor for major depression (OR = 1.06; 95% CI = 1.00 to 1.12; p = 0.0469) in reverse MR. After adjusting smoking (OR = 1.46; 95% CI = 1.19 to 1.65; p = 0.0032) and body mass index (OR = 1.44; 95% CI = 1.09 to 1.81; p = 8.56×10-04 ), the casual association between major depression and KHOA remained.

CONCLUSION

Our study indicates that major depression is a great risk factor for KHOA, increasing the likelihood of their occurrence. However, further in-depth studies will be required to validate these results and elucidate the underlying molecular mechanisms.

The role of inflammatory biomarkers in the association between rheumatoid arthritis and depression: a Mendelian randomization study

BACKGROUND

Inflammation may mediate the co-pathogenesis of rheumatoid arthritis (RA) and depression because inflammatory cytokines are associated with RA and depression. However, traditional observational research was not able to address problems with residual confusion and reverse causality.

METHODS

We summarized and retrieved 28 inflammatory cytokines associated with RA, depression, or RA with depression through a literature search. The summary statistics from genome-wide association studies for RA, inflammatory biomarkers, broad depression, and major depression disease phenotypes were used. Mendelian randomization was performed to assess the causal association between RA and inflammatory biomarkers, as well as the effects of inflammatory biomarkers on depression. Bonferroni correction was used to reduce the possibility of false positive results.

RESULTS

The study found that evidence for associations of genetically predicted RA was associated with higher levels of interleukin (IL)-9 (OR = 1.035, 95%CI = 1.002-1.068, P = 0.027), IL-12 (OR = 1.045, 95%CI = 1.045-1.014, P = 0.004), IL-13 (OR = 1.060, 95%CI = 1.028-1.092, P = 0.0001), IL-20 (OR = 1.037, 95%CI = 1.001-1.074, P = 0.047), and IL-27 (OR = 1.017, 95%CI = 1.003-1.032, P = 0.021). The level of IL-7 (OR = 1.029, 95%CI = 1.018-1.436, P = 0.030) was significantly related to RA. Only the analysis results between RA and IL-13 were satisfied with the statistical significance threshold corrected by Bonferroni (P < 0.002). However, a causal effect was not found between inflammatory biomarkers and depression.

CONCLUSIONS

In the current study the inflammatory cytokines associated with RA comorbid depression may not be the mediators that directly lead to the co-pathogenesis of RA and depression.