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JACI Highlights - January 2004
Distinguishing asthma phenotypes: Role of age at onset and eosinophilic inflammation
Asthma is a heterogeneous grouping of syndromes, yet no previous studies have integrated clinical, immunologic, physiologic and pathologic characteristics to better define the syndromes or "phenotypes". The study by Miranda, et. al, in the January 2004 edition of the Journal of Allergy and Clinical Immunology categorized severe asthma subjects by age at onset, dividing the subjects into those with onset before age 12 and at age 12 and above. These two groups were then further differentiated by presence or absence of lung eosinophils. Early onset disease was associated with strong allergic responses, but less eosinophilic inflammation than late onset disease. When eosinophilic inflammation was present, it was associated with high levels of lymphocytic and mast cell inflammation, as well as greater airway obstruction and symptoms than early onset disease without eosinophils However, even early onset subjects with no evidence for ³inflammation² remained symptomatic with marked airway obstruction. Late onset asthma had tissue eosinophilia in a greater percentage of subjects and, despite a shorter duration of disease, worse lung function than early onset disease. The high degree of eosinophilic inflammation in late onset disease appeared to be a more isolated abnormality with less lymphocytic/mast cell inflammation, but high leukotriene levels. Finally, late onset disease without eosinophils did not demonstrate the subepithelial basement membrane thickening associated with asthma, suggesting it may be a different disease entirely. Thus, 4 different severe asthma phenotypes may exist, each of which may be poorly steroid responsive for very different reasons. Genetic and therapeutic approaches to these groups are likely to be different.
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