The risk was most pronounced in patients with high MBL concentrations, IgG deficiency and 14 days of glucocorticoid treatment pointing towards an interactive effect of MBL and IgG deficiency in the presence of prolonged glucocorticoid treatment duration [Relative excess risk due to interaction 2.13 (95% CI − 0.41–4.66, p = 0.10)]. The gene discussed is MBL2; the disease is Decreased circulating IgG concentration.