Confounding and bias in observational studies in inflammatory bowel disease: a meta-epidemiological study

Target Trial Emulation: Improving the Quality of Observational Studies in Inflammatory Bowel Disease Using the Principles of Randomized Trials

The past decade has seen a substantial increase in the number of randomized controlled trials (RCTs) conducted in inflammatory bowel disease (IBD). Randomized controlled trials are the gold standard method for generating robust evidence of drug safety and efficacy but are expensive, time-consuming, and may have ethical implications. Observational studies in IBD are often used to fill the gaps in evidence but are typically hindered by significant bias. There are several approaches for making statistical inferences from observational data with some that focus on study design and others on statistical techniques. Target trial emulation is an emerging methodological process that aims to bridge this gap and improve the quality of observational studies by applying the principles of an ideal, or "target," randomized trial to routinely collected clinical data. There has been a rapid expansion of observational studies that have emulated trials over the past 5 years in other medical fields, but this has yet to be adopted in gastroenterology and IBD. The wealth of nonrandomized clinical data available through electronic health records, patient registries, and administrative health databases afford innumerable hypothesis-generating opportunities for IBD research. This review outlines the principles of target trial emulation, discusses the merits to IBD observational studies in reducing the most common biases and improving confidence in causality, and details the caveats of using this approach.

Microbiota signatures and mucosal healing in the use of enteral nutrition therapy v. corticosteroids for the treatment of children with Crohn's disease: a systematic review and meta-analysis

Corticosteroids (CS) and exclusive and partial enteral nutrition (EEN and PEN) are effective therapies in paediatric Crohn's disease (CD). This systematic review of randomised controlled trials (RCT) and cohort studies analyses the impact of EEN/PEN v. CS on intestinal microbiota, mucosal healing as well as other clinically important outcomes, including clinical remission, relapse, adherence, adverse events and health-related quality of life (HRQL) in paediatric CD. Three RCT (n 76) and sixteen cohort studies (n 1104) compared EEN v. CS. With limited available data (one RCT), the effect on intestinal microbiome indicated a trend towards EEN regarding Shannon diversity. Based on two RCT, EEN achieved higher mucosal healing than CS (risk ratio (RR) 2·36, 95 % CI (1·22, 4·57), low certainty). Compared with CS, patients on EEN were less likely to experience adverse events based on two RCT (RR 0·32, 95 % CI (0·13, 0·80), low certainty). For HRQL, there was a trend in favour of CS based on data from two published abstracts of cohort studies. Based on thirteen cohort studies, EEN achieved higher clinical remission than CS (RR 1·18, 95 % CI (1·02, 1·38), very low certainty). Studies also reported no important differences in relapse and adherence. Compared with CS, EEN may improve mucosal healing with fewer adverse events based on RCT data. While limited data indicate the need for further trials, this is the first systematic review to comprehensively summarise the data on intestinal microbiome, mucosal healing and HRQOL when comparing enteral nutrition and CS in paediatric CD.

Mendelian Randomization Rules Out Causation Between Inflammatory Bowel Disease and Non-Alcoholic Fatty Liver Disease

Background: Inflammatory bowel disease (IBD) and non-alcoholic fatty liver disease (NAFLD) usually co-exist clinically. However, whether such association is causal is still unknown.

Methods: Genetic variants were extracted as instrumental variables from the largest genome-wide association study (GWAS) of IBD, Crohn’s disease (CD) and ulcerative colitis (UC) with 25,042 cases and 34,915 controls (GWAS p-value < 5 × 10⁻⁸). Information of genetic variants in NAFLD was extracted from a GWAS with 1,483 cases and 17,781controls. Also, liver fat content (LFC) was included as the outcome. Then, a bi-direction Mendelian randomization (MR) was carried out to appraise the causal relationship between NAFLD on IBD. Besides, a multivariable MR (MVMR) design was carried to adjust for body mass index (BMI) and type 2 diabetes (T2D) as well.

Results: Generally, IBD might not affect the risk of NAFLD (OR = 0.994 [0.970, 1.019]), together with its subtypes including UC and CD. However, genetically-elevated risk of IBD might cause liver fat accumulation (beta = 0.019, p-value = 0.016) while turning insignificant at Bonferroni correction. Besides, no causal effect of NAFLD on IBD was observed (OR = 0.968 [0.928, 1.009]), together with UC and CD. Also, genetically-elevated LFC could not impact IBD, UC and CD either. The MR CAUSE analysis supported these null associations and MVMR analysis also supported such null associations even after adjusting for BMI and T2D.

Conclusion: This MR study ruled out the causal relationship between IBD and NAFLD, suggesting therapeutics targeting NAFLD might not work for IBD and vice versa.