Some of these investigations may also be used in determining exacerbations and monitoring treatment efficacy.7,16, –18 Total serum IgE levels can be used to monitor treatment with reductions in IgE of 25–50% correlating with improved symptoms and radiological appearances and increasing levels (e.g. a doubling in IgE level) suggesting an impending exacerbation.15 In addition, lung function can be used to determine the severity of underlying lung disease and monitor response to treatment. The gene discussed is IGHE; the disease is lung disorder.