Familial co-aggregation of schizophrenia and eating disorders in Sweden and Denmark

Eating disorders and schizophrenia are both moderately to highly heritable and share significant genetic risk despite distinct diagnostic criteria. Large-scale family studies on the co-aggregation of these disorders are lacking. Thus, we aimed to estimate the co-occurrence and familial co-aggregation of these disorders within the entire Swedish and Danish population. The proband cohort consisted of individuals born in Sweden (1977-2003) and Denmark (1984-2006) and still residing in their respective country at age six (N_Sweden = 2,535,191, N_Denmark = 1,382,367). Probands were linked to their biological parents, siblings, grandparents, uncles/aunts, and cousins. Diagnoses for anorexia nervosa (AN) and other eating disorders (OED: bulimia nervosa, binge-eating disorder, and eating disorder not otherwise specified) for probands and schizophrenia diagnoses for both probands and relatives were obtained. The likelihood of having schizophrenia in those with AN or OED and their relatives was compared with individuals without eating disorder diagnoses and their relatives. Probands with AN or OED were more likely to have schizophrenia than probands without these disorders. All relatives of probands with AN or OED (except parents and uncles/aunts of probands with AN) were at increased risk of schizophrenia. In general, the magnitude of odds ratios attenuated with decreasing genetic relatedness. These results suggest familial liability contributes to the association between eating disorders and schizophrenia. Clinicians should be mindful of this comorbid and co-aggregation pattern as it may influence case conceptualization and treatment decisions.