What is the evidence for interactions between filaggrin null mutations and environmental exposures in the aetiology of atopic dermatitis? A systematic review

Summary Background Epidemiological studies indicate that gene–environment interactions play a role in atopic dermatitis (AD). Objectives To review the evidence for gene–environment interactions in AD aetiology, focusing on filaggrin (FLG) loss‐of‐function mutations. Methods A systematic search from inception to September 2018 in Embase, MEDLINE and BIOSIS was performed. Search terms included all synonyms for AD and filaggrin/FLG; any genetic or epidemiological study design using any statistical methods were included. Quality assessment using criteria modified from guidance (ROBINS‐I and Human Genome Epidemiology Network) for nonrandomized and genetic studies was completed, including consideration of power. Heterogeneity of study design and analyses precluded the use of meta‐analysis. Results Of 1817 papers identified, 12 studies fulfilled the inclusion criteria required and performed formal interaction testing. There was some evidence for FLG–environment interactions in six of the studies (P‐value for interaction ≤ 0·05), including early‐life cat ownership, older siblings, water hardness, phthalate exposure, higher urinary phthalate metabolite levels (which all increased AD risk additional to FLG null genotype) and prolonged breastfeeding (which decreased AD risk in the context of FLG null genotype). Major limitations of published studies were the low numbers of individuals (ranging from five to 94) with AD and FLG loss‐of‐function mutations and exposure to specific environmental factors, and variation in exposure definitions. Conclusions Evidence on FLG–environment interactions in AD aetiology is limited. However, many of the studies lacked large enough sample sizes to assess these interactions fully. Further research is needed with larger sample sizes and clearly defined exposure assessment. Linked Comment: Park and Seo. Br J Dermatol 2020; 183:411.
What's already known about this topic? Gene–environment interactions are considered important in the aetiology of atopic dermatitis.Loss‐of-function mutations in the gene coding filaggrin (FLG) are the most consistently reported genetic variants for atopic dermatitis.Studies have reported evidence for gene–environment interaction involving FLG and a range of different environmental exposures. What does this study add? There is some evidence for FLG–environment interactions in the aetiology of atopic dermatitis; however, the evidence is limited.Studies lack large enough sample sizes to achieve adequate power in order to assess these interactions fully. Linked Comment: Park and Seo. Br J Dermatol 2020; 183:411. Plain language summary available online