In this study, we analyzed data from a large birth cohort of OCD and TD/CTD cases derived from the Swedish population-based registers to address the following questions: 1) are patients with OCD and/or TD/CTD more likely to have comorbid AD, compared to population controls?; 2) are biological relatives of patients with OCD and/or TD/CTD more likely to have AD, compared to relatives of unaffected individuals?; 3) does the familial risk decrease with increasing genetic distance?; and 4) do mothers have higher risks than fathers or other first-degree relatives?
