DISTRIBUTION AND HERITABILITY OF RECURRENT EAR INFECTIONS

The distribution of recurrent ear infections was obtained from a popul ation-based sample of 2,750 pairs of Norwegian twins born between 1967 and 1974. The lifetime prevalence of self-reported recurrent ear infe ctions was 8.9%, with a significant predominance of female cases. The mean age of onset was 4.2 years, with a gradual decrease in occurrence from 2 to 7 years of age. Among monozygotic pairs, the rate of tetrac horic correlation between co-twins was almost identical in males (0.73 , SE 0.08) and females (0.74, SE 0.06), but among the dizygotic pairs the correlation was clearly higher in males (0.53, SE 0.12) than in fe males (0.20, SE 0.12). The value in the unlike-sexed dizygotic twins ( 0.25, SE 0.05) was intermediate to that of the like-sexed male and fem ale dizygotic pairs. The relative contribution of genes and environmen t to variability in the predisposition to develop otitis media was est imated by means of structural equation modeling. Variation in liabilit y to ear infections was mainly explained by additive genetic and domin ance factors in females, for whom heritability was estimated at 74%. T he remaining 26% of the variation in liability was explained by indivi dual environmental factors. In males, 45% of the variation could be ac counted for by genetic factors, 29% by common familial environment, an d the remaining 26% by individual environmental effects.