We estimated the heritability of AD, the individual DSM-IV criteria, as well as two continuous phenotypes based on the LCA probabilities. The estimated heritability for AD (61%) was similar to previous reports (Prescott et al., 2006). However, the heritability estimates for the individual DSM-IV criteria were slightly larger than previously reported (Slutske et al., 1999). This may reflect the effects of shared environment, which is known to inflate the estimate of the genetic contribution to the trait (Tenesa and Haley, 2013). Although the phenotypes based on the probabilities of class assignment were less heritable (≤ 34%), actual membership in each class was more heritable (≥52%). This may be related to the entropy such that misclassification may have favored the assignment of related individuals into the same class. The less heritable moderate risk class (17%) could be a result of environmental influences, and therefore was not examined further.
