Bronchial reactivity and allergy-promoting factors in monozygotic twins discordant for allergic rhinitis.

Bronchial reactivity was studied twice in eight monozygotic twin pairs discordant for allergic rhinitis with pollen hypersensitivity, during the winter season (all eight pairs) and during the pollen season (seven pairs). On both occasions, the allergic twins showed significantly higher reactivity than their nonallergic siblings. The results indicate that moderate allergic rhinitis is associated with increased bronchial reactivity. This increased reactivity is an acquired trait; however, bronchial reactivity is not constantly increased in pollen rhinitis and may be normal even during the pollen season. The symptoms of allergic rhinitis usually started in childhood before the separation of the siblings. We could not demonstrate any major differences in exposure to allergens or airway irritants between the siblings. The allergic twins tended to have lower birth weight and insufficient weight increase just after birth.