Increases in multiple psychiatric disorders in parents and grandparents of patients with bipolar disorder from the USA compared with the Netherlands and Germany

Objective We previously found that compared with Europe more parents of the USA patients were positive for a mood disorder, and that this was associated with early onset bipolar disorder. Here we examine family history of psychiatric illness in more detail across several generations. Methods A total of 968 outpatients (average age 41) with bipolar disorder from four sites in the USA and three in the Netherlands and Germany (abbreviated as Europe) gave informed consent and provided detailed demographic and family history information on a patient questionnaire. Family history of psychiatric illness (bipolar disorder, unipolar depression, suicide attempt, alcohol abuse, substance abuse, and other illness) was collected for each parent, four grandparents, siblings, and children. Results Parents of the probands with bipolar disorder from the USA compared with Europe had a significantly higher incidence of both unipolar and bipolar mood disorders, as well as each of the other psychiatric conditions listed above. With a few exceptions, this burden of psychiatric disorders was also significantly greater in the grandparents, siblings, and children of the USA versus European patients. Conclusion The increased complexity of psychiatric illness and its occurrence over several generations in the families of patients with bipolar disorder from the USA versus Europe could be contributing to the higher incidence of childhood onsets and greater virulence of illness in the USA compared with Europe. These data are convergent with others suggesting increased both genetic and environmental risk in the USA, but require replication in epidemiologically-derived populations with data based on interviews of the family members.