All patients must be able to give informed consent. The definition of the severity of their asthma will be according to the GINA (Global Initiative for Asthma) guidelines dependent on the amount of therapy needed to control asthma. The investigators will also include at least 45 patients with severe asthma defined on the basis of: Uncontrolled asthma: three or more of the following features present in any week in the previous 4 weeks: