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Background Loss of response (LOR) to tumour necrosis factor antagonists (anti-TNF) occurs in up to 50% of patients with inflammatory bowel disease (IBD). The ability to predict which patients are likely to lose response would allow therapies to be tailored to the patient’s characteristics. Immunogenicity is a common cause of LOR. Recently, a GWAS performed using the PANTS cohort demonstrated that carriage of one or more HLA-DQA1*05 alleles confers an increased risk of immunogenicity to anti-TNF therapy (Sazonovs et al. Gastroenterology 2019). We found that HLA-DQA1*05 carriage also identified patients at increased risk of clinical LOR to infliximab (Guardiola et al. ECCO 2019). The aim of our study was to know if carriage of a HLA-DQA1*05 allele is also associated with secondary LOR to adalimumab (ADA) in patients with Crohn’s disease (CD). Methods This is a retrospective cohort study from a prospectively maintained data base. Patients were included if they had achieved response to ADA. LOR was defined as recurrence or worsening of IBD-related symptoms that required a change or intensification in treatment, hospitalisation or surgery. Independent predictors of LOR were identified using univariate and multivariable Cox proportional hazard regression. Results We included 53 patients with Crohn’s disease, followed up to LOR (n = 31, 58%) or a median of 51 months (IQR 35–74). Forty-five per cent were carriers of an HLA-QA1*05 allele. HLA-DQA1*05 carriage was associated with LOR both, upon univariate analysis (HR 2.1 (95% CI 1.1–4.3), p = 0.04) and upon multivariate analysis, after adjusting for immunomodulators use, smoking status and BMI (HR 2.74 (95% CI 1.2–6.2), p = 0.02) (Figure 1). The cumulative persistence rates of ADA after adjusting for immunomodulators use was significantly lower in HLA-DQA1*05 carriers compared with non-carriers (HR 4 (95% CI 1.2–15.5), p = 0.02) (Figure 2). Conclusion HLA-DQA1*05 carriage is frequent and it is associated with a marked increase in the risk of LOR to ADA. HLA-DQA1*05 may become a clinically meaningful genetic marker that could allow for treatment to be tailored according to the risk of LOR, which is a step towards personalised medicine.