biostudies-literatureUnknown64(1)Ohi K<h4>Background</h4>Intelligence is inversely associated with schizophrenia (SCZ) and bipolar disorder (BD); it remains unclear whether low intelligence is a cause or consequence. We investigated causal associations of intelligence with SCZ or BD risk and a shared risk between SCZ and BD and SCZ-specific risk.<h4>Methods</h4>To estimate putative causal associations, we performed multi-single nucleotide polymorphism (SNP) Mendelian randomization (MR) using generalized summary-data-based MR (GSMR). Summary-level datasets from five GWASs (intelligence, SCZ vs. control [CON], BD vs. CON, SCZ + BD vs. CON, and SCZ vs. BD; sample sizes of up to 269,867) were utilized.<h4>Results</h4>A strong bidirectional association between risks for SCZ and BD was observed (odds ratio; ORSCZ → BD = 1.47, p = 2.European psychiatry : the journal of the Association of European Psychiatristse61https://www.ebi.ac.uk/biostudies/studies/S-EPMC8516746biostudies-literatureCausal associations of intelligence with schizophrenia and bipolar disorder: A Mendelian randomization analysis.PMC8516746Ohi KSugiyama STakai KShioiri TKitaichi KKuramitsu ASoda MfalseCausal associations of intelligence with schizophrenia and bipolar disorder: A Mendelian randomization analysis.<h4>Background</h4>Intelligence is inversely associated with schizophrenia (SCZ) and bipolar disorder (BD); it remains unclear whether low intelligence is a cause or consequence. We investigated causal associations of intelligence with SCZ or BD risk and a shared risk between SCZ and BD and SCZ-specific risk.<h4>Methods</h4>To estimate putative causal associations, we performed multi-single nucleotide polymorphism (SNP) Mendelian randomization (MR) using generalized summary-data-based MR (GSMR). Summary-level datasets from five GWASs (intelligence, SCZ vs. control [CON], BD vs. CON, SCZ + BD vs. CON, and SCZ vs. BD; sample sizes of up to 269,867) were utilized.<h4>Results</h4>A strong bidirectional association between risks for SCZ and BD was observed (odds ratio; ORSCZ → BD = 1.47, p = 2.2021-01-01T00:00:00Z2021 Oct2025-04-04T22:43:10.135Z2025-04-04T22:43:10.135ZS-EPMC85167463464199010.1192/j.eurpsy.2021.2237