HAY-FEVER - A FINNISH NATIONWIDE STUDY OF ADOLESCENT TWINS AND THEIR PARENTS

Background Like other atopic diseases, hay fever is known to cluster i n families. This clustering is due either to effects of a shared famil y environment or to genetic inheritance. By comparing the occurrence o f hay fever among monozygous (MZ) and dizygous (DZ) twin pairs, we wer e able to estimate the contribution of genetic and environmental facto rs in the development of hay fever. Methods A questionnaire mailed to a nationwide sample of 2483 families with 16-year-old twins furnished data for the cumulative incidence of physician-diagnosed hay fever amo ng these adolescents and their parents. Results Among the 1765 twin pa irs with data available for analysis, hay fever was reported for 14.1% of boys (95% CI=12.4-15.8%) and 10.0% of girls (95% CI=8.6-11.4%). Th e MZ twin pairs (probandwise concordance rate=60.3%, 95% CI=52-68%) we re significantly more concordant for hay fever than were DZ twin pairs (31.5%, 95% CI=26-36%). Genetic factors accounted for 74-82% of the i nterindividual variability in liability to hay fever, variation in sha red family environment for 7% at most, and unique (individual) environ ment for 18%. Conclusions Familial occurrence of hay fever is mainly d ue to genes predisposing to the trait. Environmental exposures shared in common by family members but varying between families appear to acc ount for at most a modest proportion of the variability in risk of dev eloping hay fever.