Definition of AD and AD phenotype
Children were stratified into early childhood (0–3 years), preschool
(4–6 years), and school-age (7–9 years) groups. AD was considered
present if a diagnosis was constituted at any period within the
specified age group. Current AD was determined as a diagnosis within the
age group and the presence of AD symptoms confirmed by a physician
within the previous 12 months. Our study targeted various phenotypes,
including the: early-transient, defined as AD onset within 2 years of
age and no further symptoms; early-persistent, defined as AD onset
within 2 years of age and symptoms not improving within 2 years; and
late-onset, defined as AD onset after 2 years of age(13).