We first linked information about biological parents to our cohort and analyzed the risk of any AD (and also specific AD) in parents of individuals affected with OCD and TD/CTD compared to parents of unaffected individuals. For the sibling and cousin analyses we used the same birth cohort as when studying the individual risk (born between 1940 and 2007). Full siblings were defined as individuals who share two biological parents and half siblings were defined as individuals who share one parent. Cousin analyses only included full cousins, defined as having a common grandfather and grandmother. All analyses adjusted for birth year and gender of the index person as well as for birth year of the parent/sibling/cousin.
