More assortative mating in US compared to European parents and spouses of patients with bipolar disorder: implications for psychiatric illness in the offspring.

The effect of assortative mating on offspring is often not considered. Here, we present data on illness in the spouse and the parents of patients with bipolar disorder as they affect illness in the offspring. A history of psychiatric illness (depression, bipolar disorder, suicide attempt, alcohol abuse, drug abuse, and "other" illness) was elicited for the parents, spouse, and the offspring of 968 patients with bipolar disorder (540 of whom had children) who gave informed consent for participation in a treatment outcome network. Assortative mating for a mood disorder in the spouse and parents in those from the United States (US) was compared to those from the Netherlands and Germany and related to illnesses in the offspring. There was more illness and assortative mating for a mood disorder in both the spouse and patient's parents from the US compared to Europe. In the parents of the US patients, assortative mating for a mood disorder was associated with more depression, bipolar disorder, alcohol, and "other" illness in the offspring. Compared to the Europeans, there was more assortative mating for mood and other disorders in two generations of those from the US. This bilineal positivity for a parental mood disorder was related to more depression a second generation later in the patients' offspring. In clinical assessment of risk of illness in the offspring, the history of psychiatric illness in the spouse and patient's parents might provide additional information.