Types of asthma and wheezing.

There is now convincing evidence that childhood asthma is a spectrum of different conditions that are manifested by recurrent symptoms of bronchial obstruction. Risk factors such as age, genetic background, degree of maturation at birth and allergic sensitization, amongst others, are important in determining asthma-like manifestations at different times during childhood. Although efforts have been made to differentiate "wheezing syndromes" occurring during childhood, these efforts have been made more difficult by the significant degree of overlap between them. Nevertheless, the evidence suggests that recurrent obstructive symptoms remit in a large number of children who develop these symptoms during the first 3 yrs of life, and low lung function seems to be the main risk factor for these transient episodes. On the other hand, children who will go on to develop persistent wheezing beyond infancy and early childhood usually have a family history of asthma and allergies and present with allergic symptoms very early in life. Recent studies suggest that the latter also show acute immune responses to viruses that are different from those of transient wheezers. Identification of specific inflammatory markers for persistent wheezing at the time of the first lower respiratory symptoms may be a necessary step for the establishment of successful strategies for the prevention of asthma in the future.