A detailed description of the protocol has been published elsewhere ( 25).

Our study included mother-child pairs from Project Viva, a prospective longitudinal pre-birth cohort in Boston, Massachusetts. We further postulated that maternal lifestyle factors during pregnancy may impact the epigenetic clock trajectory toward allergen sensitization in mid-childhood.

We hypothesized that older DNAmAge and age acceleration (including IEAA and EEAA) are associated with higher risks of mid-childhood allergy and asthma. We considered both extrinsic epigenetic age acceleration (EEAA) and intrinsic epigenetic age acceleration (IEAA) to best capture the age-associated metrics reflective and independent of age-related changes in cell count, respectively ( 3, 8, 13). In this study, we sought to evaluate the associations of DNAmAge and epigenetic age acceleration (estimated at birth, early-childhood and mid-childhood) with mid-childhood allergic phenotypes (including total serum IgE, atopic sensitization, environmental allergen sensitization, food allergen sensitization, and asthma) in Project Viva-a longitudinal pre-birth cohort in Boston, Massachusetts.

Since the epigenetic clock likely captures a higher order property of the methylome ( 24) and reflects the immunologic and developmental components of biological aging, DNA methylation age (DNAmAge) may serve as a molecular marker of allergy and asthma in children. Studying epigenetic signatures at birth or in early childhood has also been postulated as a molecular approach to distinguish transient wheezing from early asthma symptoms, and help to define age-associated disease endotypes ( 23). Epigenetic mechanisms may mark allergic disease susceptibility, and play a role in the onset, progression and manifestations of allergy and asthma ( 18вЂ“ 22). However, chronological age alone does not fully explain disease variability. The development of allergic diseases is likely age-dependent during childhood, beginning in some children with food allergy and atopic dermatitis (infancy to early-childhood), followed by allergic asthma and rhinitis (early to mid-childhood) ( 15вЂ“ 17). Intrinsic epigenetic age acceleration measures epigenetic aging independent of major blood immune cell counts, while EEAA weights blood cell types that are known to change with age, including naГЇve cytotoxic T cells (CD45RA+ CCR7+), exhausted cytotoxic T cells (CD28-CD45RA-), and plasma B cells, and measures epigenetic aging in immune-related domains ( 8, 13, 14). Further, two other epigenetic clock calculations-intrinsic epigenetic age acceleration (IEAA) and extrinsic epigenetic age acceleration (EEAA)-have also not been linked to childhood allergic diseases. However, epigenetic age and epigenetic age acceleration residuals have not been studied in association with allergy and asthma in children. Epigenetic age acceleration residuals (the residuals from a linear regression of DNA methylation age on chronological age) are also prospectively associated with faster increase in weight during childhood and adolescence ( 10), and are predictive of earlier pubertal development in young girls ( 12). Studies have demonstrated that birth weight ( 9), birth by Caesarean section ( 9), and other pregnancy-related exposures (maternal smoking, body mass index (BMI), selenium and cholesterol levels) ( 9) associate with higher DNAmAge in children (age range 7 to 19). More recently, research on the epigenetic clock has been expanded into the early-life spectrum ( 9вЂ“ 12). These epigenetic clock metrics have also predicted cancer, cardiovascular and all-cause mortality independent of chronological age ( 5вЂ“ 8). An increasing body of evidence suggests that DNA methylation derived epigenetic clock metrics (which include DNA methylation age (DNAmAge) and epigenetic age acceleration) cross-sectionally associate with adult diseases including physical and cognitive decline ( 2), and ParkinsonвЂ™s disease ( 3) and are predictive of future onsets of lung cancer ( 4). DNA methylation serves as a molecular marker for biological aging and its manifestations ( 1).

Biological age versus chronological age