DesignMendelian randomization study.Case selectionUsing a Mendelian randomization framework, the causal relationship between periodontitis [chronic periodontitis (CP) and aggressive periodontitis (AgP)] and ischemic stroke and its subtypes [cardioembolic (CE) stroke, large artery atherosclerosis (LAA), and small vessel occlusion (SVO)], were studied.Data analysisData from three large databanks, namely, UK Biobank, genome-wide association study of European ancestry, and MEGASTROKE consortium of European ancestry were used to obtain genetic variant information of CP, AgP, and ischemic stroke, respectively. UK Biobank contributed 950 cases of CP and 455,398 controls. Genome-wide association study of European ancestry contributed 851 AgP cases and 6836 controls. MEGASTROKE consortium of European ancestry contributed 34,217 cases of ischemic stroke and its subtypes and 406,111 controls. Statistical tests including inverse variant weighted method and sensitivity analyses were performed to analyse the causal inference and to verify the strength of the results.ResultsA total of 15 single nucleotide polymorphisms (SNPs) for CP was obtained as genetic instruments. No causal inference of CP on ischemic stroke was found. Among the ischemic stroke subtypes, with the exception of CE stroke, no significant causal inference of CP on LAA or SVO was found. A total of 9 single nucleotide polymorphisms (SNPs) for AgP was obtained as genetic instruments. No causal inference of AgP on ischemic stroke and its subtypes were found.ConclusionsNeither CP nor AgP was found to have a causal inference on ischemic stroke and most of its subtypes. A probable causal effect of CP on CE stroke was noted.