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Letter to the editor: Genetically determined IBD is associated with decreased risk of Alzheimer’s disease: a Mendelian randomisation study
  1. Xingzhi Guo1,2,
  2. Li Chong1,2,
  3. Xin Zhang1,2,
  4. Rui Li1,2,3
  1. 1Department of Geriatric Neurology, Shaanxi Provincial People's Hospital, Xi'an, Shaanxi, China
  2. 2Shaanxi Provincial Clinical Research Center for Geriatric Medicine, Xi'an, Shaanxi, China
  3. 3Institute of Medical Research, Northwestern Polytechnical University, Xi'an, Shaanxi, China
  1. Correspondence to Dr Rui Li, Department of Geriatric Neurology, Shaanxi Provincial People's Hospital, Xi'an, Shaanxi, China; rli{at}

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We read with great interest the observation of eminent colleague Chen et al showing that patients with IBD had a higher incidence of dementia, particularly Alzheimer’s disease (AD, HR=6.19).1 Due to various confounding factors (age of onset, treatment, smoking, body mass index, etc), it is usually hard to evaluate the causal link between IBD and AD using observational studies. Two-sample Mendelian randomisation (MR) treated genetic variants as instrumental variables (IVs) for exposures, effectively minimising the impact of confounding factors.

Using two-sample MR analysis, we adopt the publicly available summary statistics from large-scale genome-wide association studies (GWAS) to investigate the causal effect of IBD (Ncases=12 882; Ncontrols=21 770),2 including UC and Crohn’s disease (CD), on AD (Ncases=21 982, Ncontrols=41 944) of European descent.3 Briefly, single-nucleotide polymorphisms (SNPs) with p values less than 5E–08 for IBD were selected as IVs and were clumped based on the linkage disequilibrium (LD) structure (R2 <0.0001 within 10 000 kb, the 1000 Genomes Project European panel). In …

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  • Contributors XG and LC conceived and designed the project. XZ and XG collected and analysed the data and drafted the manuscript. RL revised the manuscript. All authors approved the final letter.

  • Funding This work was supported by the Project for Sanqin Academic Innovation Team in Shaanxi Province (SQ0157).

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.

  • Provenance and peer review Not commissioned; internally peer reviewed.

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