Study of Bidirectional Causal Relationships Between Pain and Mental Disorders," recently published in the Journal of Pain Research. 1 Using bidirectional Mendelian randomization (MR) combined with multivariable MR approaches, the authors investigated potential causal relationships between multiple pain phenotypes and a wide range of mental and personality disorders.By integrating several large genome-wide association study (GWAS) datasets and incorporating adjustments for potential confounders such as obesity, insomnia, and substance use, the study provides valuable genetic evidence supporting the complex bidirectional interaction between pain and psychiatric conditions.The authors should be commended for their comprehensive analytical framework and for extending MR investigations beyond commonly examined conditions such as depression and anxiety.Nevertheless, several methodological considerations may help further contextualize the interpretation of these findings.First, the definition of several pain phenotypes may introduce heterogeneity that could influence causal inference.In particular, many exposure variables-especially the "recent pain" traits-were derived from selfreported questionnaire data within the UK Biobank.While this approach enables large-scale population analysis, self-reported pain is inherently subjective and may be influenced by recall bias, individual pain perception, and psychological status.The authors correctly identified the use of binary phenotype definitions as an important limitation.The available GWAS datasets lacked detailed information regarding pain intensity, pain chronicity, functional impairment, and severity of psychiatric symptoms.Consequently, the reported causal estimates may not fully capture the heterogeneity of clinical pain experiences or mental disorders.Future investigations incorporating more refined phenotypic characterization may provide additional insights into whether causal effects vary according to disease severity or symptom burden. 2 Second, we commend Liang and Fan for their rigorous assessment of horizontal pleiotropy.They employed multiple complementary methods-including MR-Egger (intercept test), MR-PRESSO (outlier detection and correction), weighted median estimation, and leave-one-out analyses-and found no evidence of directional pleiotropy.This comprehensive approach substantially mitigates concerns that pleiotropy might drive their findings.As a forward-looking suggestion for future MR studies in pain-psychiatry research, we note that newer methods such as MR-RAPS (robust adjusted profile score) 3 and contamination mixture models can provide additional robustness against both weak instruments and balanced pleiotropy, and may be considered when even more stringent control is desired.However, we emphasize that this is a suggestion for future methodological refinement, not a criticism of the original authors' already-thorough analysis.
Han et al. (Mon,) studied this question.