Age-of-asthma onset as a determinant of different asthma phenotypes in adults: a systematic review and meta-analysis of the literature

Abstract

Age-of-asthma onset is often used to distinguish different adult asthma phenotypes; however, similarities and differences between early- and late-onset adult asthma have not been summarized to date. Of the 2921 records found, we identified 12 studies comparing early- and late-onset current asthma in adults. Age 12 was most commonly used to delineate the two age-of-onset phenotypes. Adults with early-onset current asthma were more likely to be atopic and had a higher frequency of asthma attacks, whereas adults with late-onset disease were more likely to be female, smokers and had greater levels of spirometrically defined fixed airflow obstruction. The prevalence of severe asthma was similar in both groups, and, in general, there were few phenotypic differences between severe asthmatics regardless of age of onset. Findings for several key characteristics, including lung function, were inconsistent between studies. Overall, there appears to be distinctive phenotypic differences with age of asthma onset. Although early-onset adult asthma is likely more attributable to atopy and potentially genetic factors, late-onset adult asthma appears to be more related to environmental risk factors, and so may be better targeted by preventive strategies. More detailed research is required to better characterize these phenotypes and to clarify potential clinical implications.

Keywords:

• adult asthma
• age of onset
• early-onset
• late-onset
• phenotypes

Financial & competing interests disclosure

EH Walters, CJ Lodge, AJ Lowe, MC Matheson and SC Dharmage are supported by National Health and Medical Research Council of Australia, and JL Perret is supported by an Australian Postgraduate award and Australian Lung Foundation. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Adult asthma is a heterogeneous condition, containing a number of potential subgroups or phenotypes with distinct characteristics.

• Although classification of adult asthma into early- and late-onset is widely used in the literature, the similarities and differences of these two phenotypes have not been summarized to date.

• This review finds that adults with early-onset current asthma were more likely to be atopic and have more frequent symptoms compared with adults with late-onset disease, who were more likely female, smokers and had greater levels of fixed airflow obstruction.

• The prevalence of severe asthma was similar in both groups, and, in general, there were few phenotypic differences between severe asthmatics, regardless of age of onset.

• However, there was conflicting evidence for several key socio-demographic and clinical characteristics, including lung function, and limitations with the current evidence.

• Although there appears to be distinct phenotypic differences with age of asthma onset, longitudinal prospective studies are needed to more definitively characterize these adult asthma phenotypes.