Today there are two international guidelines that might help in classifying ACOS: the Spanish one that defines ACOS in the presence of two major and two minor criteria such as very positive bronchodilator test, eosinophilia in sputum, history of asthma and high total IgE, personal history of atopy and positive bronchodilator test on two or more occasions [2], and the Global Initiative for Asthma (GINA) and Global Initiative for Chronic Obstructive Lung Disease (GOLD) that foresee that an ACOS patient has a similar number of features of asthma and COPD. This evidence concerns the gene IGHE and asthma.