Background: Previous twin studies of asthma and allergy implicate both genetic and environmental factors in disease risk, but few have related the occurrence of clinical disease to objective markers of allergic sensitization in twins.
Objective: We sought to investigate the concordance and interrelationships of self-reported allergic disease and total and aeroallergen-specific IgE levels within pairs of British adult female twins.
Methods: Three hundred forty monozygotic and 533 dizygotic pairs, aged 18 to 72 years, completed questionnaires about allergic disease. Of these, 282 monozygotic and 270 dizygotic pairs were tested for total IgE and specific IgE to Der p 1, mixed grass pollen, and cat dander by means of fluoroimmunoassay.
Results: Concordance rates for all variables were higher for monozygotic than for dizygotic twins, significantly (P < .05) so for hay fever, eczema, and specific IgE positivity but not (P > .05) for self-reported asthma or allergies. Within-pair correlations of log-transformed IgE were 0.59 for monozygotic twins and 0.29 for dizygotic twins, implying heritability of 60%. Within both monozygotic and dizygotic pairs discordant for hay fever or reported allergies, the affected twin had significantly higher total and specific IgE levels. Within pairs who were doubly discordant for 3 allergic diseases, associations between diseases were of similar strength for monozygotic and dizygotic pairs.
Conclusions: These results confirm that genetic factors influence susceptibility to aeroallergen sensitization and clinical allergic disease. However, genetically identical twins are often discordant in their expression of atopy, suggesting a substantial modifying role for environmental factors.