When we performed the analysis based on those recruited during the period 2006–2009, the overall association between ever having had a head trauma and risk of MS was similar to that from the main analysis (OR 1.34, 95% CI 1.12 to 1.61), as was the interaction between recent head trauma and HLA-DRB1*15:01 (AP 0.44, 95% CI 0.14 to 0.94), and between head trauma and absence of HLA-A*02:01 (AP 0.37, 95% CI 0.01 to 0.83) with regard to MS risk. The gene discussed is HLA-A; the disease is myeloid sarcoma.