The greatest risk for atopy in infancy and young childhood is asthma or atopic disease in first-degree relatives, especially in an asthmatic mother. At least 80% of childhood asthma and all allergic rhinitis is atopic, so atopy can be assumed for most cases of asthma in the Tucson Children’s Respiratory Study.11–
In that study, the risk stemming from maternal asthma was 44.2% compared with the risk from paternal asthma (31.4%; p > 0.05). Allergic rhinitis in either parent was a risk factor for asthma in the child, but when analysis was confined to children without asthmatic parents, only allergic rhinitis in the mother remained a significant risk factor for asthma in the child. If the disease were transmissible, the more prominent role of the mother could be related to the relatively few cases developing in utero and to her role in child care. These authors also found an increased risk with prolonged breast-feeding. For unknown reasons, there is a tendency for the form taken by atopic diseases, such as atopic eczema, allergic rhinitis, asthma, and nasal polyps, to be more common in some families than in others.13
The family risk continues until early adulthood, but for new cases developing after age 25 years the presence of parental atopy loses most of its significance.14
This suggests that by then most children of an affected family have developed symptoms, have become immune, or lacked genetic susceptibility.