The estimation of heritability for twin data based on concordances of sex and disease.

Heritability is an important measure in chronic disease epidemiology. Almost all developed methods of heritability estimation for dichotomous outcomes in twin data are based on concordance of monozygous (MZ) and dizygous (DZ) twins. However, most existing twin registries, which provide a unique and efficient opportunity to assess the putative genetic basis of diseases, do not have zygosity information. We developed a method that can be used to estimate the heritability for twin data with no information on zygosity. The only conditions on using this method are that the studied disease incidence is not strongly related to sex, and the distribution of zygosity is in accordance with Weinberg's rule. Using asthma twin data which has histological confirmed zygosity, we compared the results of our method with Holzinger's formula. The heritability of asthma was 24.88% (95% CI 21.98% - 27.78%) and 29.83% (95% CI 22.28% - 37.38%) estimated by our method and Holzinger's formula respectively. We conclude that our new method can be used in the estimation of heritability with large twin register data with no zygosity information available.