Children account for less than 2% of identified cases of coronavirus disease 2019 (COVID-19).1,2 It is hypothesized that the lower risk among children is due to differential expression of angiotensin-converting enzyme 2 (ACE2),3 the receptor that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses for host entry.4 We investigated ACE2 gene expression in the nasal epithelium of children and adults.
The results from this study show age-dependent expression of ACE2 in nasal epithelium, the first point of contact for SARS-CoV-2 and the human body. Covariate-adjusted models showed that the positive association between ACE2 gene expression and age was independent of sex and asthma. Lower ACE2 expression in children relative to adults may help explain why COVID-19 is less prevalent in children.3 A limitation of this study is that the sample did not include individuals older than 60 years.
Few studies have examined the relationship between ACE2 in the airway and age. A study of bronchoalveolar lavage fluid from 92 patients with acute respiratory distress syndrome reported no association between ACE2 protein activity and age,5 but epithelial gene expression was not examined, and ACE2 protein may be variably shed into bronchoalveolar lavage fluid. Furthermore, the lung and nasal environments are distinct, with known differences in gene expression.6 This study provides novel results on ACE2 gene expression in nasal epithelium and its relationship with age.
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