2012; Takeuchi et al. 2022; Hamshere et al. 2013). Similarly, the putative risk effect of ITIH1 (IVW OR = 1.06, p = 0.013) was compromised by detectable horizontal pleiotropy (MR–Egger intercept p = 0.025), echoing inconsistencies in earlier MR studies (Psychiatric GWAS Consortium Bipolar Disorder Working Group 2011; Hu et al. 2023). Here, ITIH1 is linked to bipolar disorder.