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.
We conducted a retrospective examination of nasal epithelium from individuals aged 4 to 60 years encountered within the Mount Sinai Health System, New York, New York, during 2015-2018. Samples were collected from individuals with and without asthma for research on nasal biomarkers of asthma. The study was approved by the Mount Sinai institutional review board. Written informed consent was obtained from participants (or their parents for minors). Nasal epithelium was collected using a cytology brush that was immediately placed in RNA stabilization fluid and stored at −80 °C. RNA was isolated within 6 months. RNA samples were checked for quality and sequenced as a single batch in 2018. Sequence data processing included sequence alignment and normalization of gene expression counts across genes and samples.
Given the role of ACE2 in SARS-CoV-2 host entry,4 ACE2 gene expression was the focus of this study. Linear regression models with and without adjustment for covariates (sex and asthma) were built with ACE2 gene expression in log2 counts per million as the dependent variable and age group as the independent variable using R software, version 3.6.0 (R Foundation). Age was categorized into the following groups reflecting developmental life stages: younger children (aged <10 years), older children (aged 10-17 years), young adults (aged 18-24 years), and adults (aged ≥25 years). Two-sided tests and a significance threshold of P ≤ .05 were used. Trend pattern was evaluated using polynomial orthogonal contrasts.
The cohort of 305 individuals aged 4 to 60 years was balanced with regard to sex (48.9% male). Because the cohort had been recruited to study biomarkers of asthma, 49.8% had asthma.
We found age-dependent ACE2 gene expression in nasal epithelium (Figure). ACE2 gene expression was lowest (mean log2 counts per million, 2.40; 95% CI, 2.07-2.72) in younger children (n = 45) and increased with age, with mean log2 counts per million of 2.77 (95% CI, 2.64-2.90) for older children (n = 185), 3.02 (95% CI, 2.78-3.26) for young adults (n = 46), and 3.09 (95% CI, 2.83-3.35) for adults (n = 29).
Linear regression with ACE2 gene expression as the dependent variable and age group as the independent variable showed that compared with younger children, ACE2 gene expression was significantly higher in older children (P = .01), young adults (P < .001), and adults (P = .001) (Figure). As the distributions of sex and asthma varied among the age groups, a linear regression model adjusted for sex and asthma was built that also showed significant adjusted associations (P ≤ .05) between ACE2 expression and age group. Regression (β) coefficients for age groups from the unadjusted and adjusted models are shown in the Table. These regression coefficients indicate the difference in ACE2 expression (in log2 counts per million) between a given age group and the group of children younger than 10 years. Tests for trend using polynomial orthogonal contrasts indicated a significant linear trend for change in ACE2 expression with advancing age group (P ≤ .05).
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.
Corresponding Author: Supinda Bunyavanich, MD, MPH, Icahn School of Medicine at Mount Sinai, 1425 Madison Ave #1498, New York, NY 10029 (email@example.com).
Accepted for Publication: May 7, 2020.
Published Online: May 20, 2020. doi:10.1001/jama.2020.8707
Author Contributions: Dr Bunyavanich had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: All authors.
Acquisition, analysis, or interpretation of data: Bunyavanich, Do.
Drafting of the manuscript: Bunyavanich.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Bunyavanich, Do.
Obtained funding: Bunyavanich.
Administrative, technical, or material support: Bunyavanich.
Supervision: Bunyavanich, Vicencio.
Conflict of Interest Disclosures: Dr Vicencio reported being an investor in Filament Biosolutions. No other disclosures were reported.
Funding/Support: This study was funded by National Institutes of Health grant R01 AI118833.
Role of the Funder/Sponsor: The funding organization had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.
Additional Contributions: We thank Robert Griffin, MD, PhD, Hospital for Special Surgery, and Yoojin Chun, MS, Icahn School of Medicine at Mount Sinai, for their assistance with manuscript preparation. Dr Griffin and Ms Chun did not receive compensation for their contributions.
JM. Characteristics of and important lessons from the coronavirus disease 2019 (COVID-19) outbreak in China: summary of a report of 72 314 cases from the Chinese Center for Disease Control and Prevention. JAMA
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