The investigation of asthma phenotypes.

PURPOSE OF REVIEW: Asthma is a heterogeneous disease constituted by overlapping separate syndromes. This review discusses recent published data relevant to asthma and severe asthma classification, resting either on the 'candidate' approach based on criteria chosen by experts or on the 'exploratory' approach based on unsupervised statistical methods. RECENT FINDINGS: Following the 'candidate' approach, groups of experts recently reviewed the classification of severe asthma to be applicable in low-income, milddle-income, and high-income countries and provided a systematic algorithm to diagnose severe refractory asthma. The concept of asthma endotypes involving different biological mechanisms has recently being proposed. Results from the 'exploratory' approach support the clinical heterogeneity in severe asthma and the need for new approaches for the classification of asthma severity. The novel childhood and adult asthma phenotypes recently identified using the exploratory approach were supported by first evidence of validity (replication in independent studies, assessment of their discriminative properties, and effect on clinical prognosis). SUMMARY: Research on asthma phenotypes has increased exponentially in the last year. The main focus has been on severe asthma, likely due to its clinical and socioeconomic burden. Interestingly, many of the phenotypes identified are stable across populations and methodological approaches. Further analyses on the asthma phenotypes are needed to address their stability over time and their relevance from clinical and etiological perspectives.