People with psychiatric disorders may be likely to marry and have children with other people who also have psychiatric disorders, according to a new study from Sweden.
The study did not examine why people with psychiatric conditions, such as schizophrenia and depression, may tend to mate with other people with such conditions, and therefore, the mechanisms behind this phenomenon are not clear, said Ashley E. Nordsletten, a co-author of the study and a postdoctoral research fellow at Karolinska Institutet in Stockholm.
But one possible reason is that people may simply select partners who share certain traits with them, she told Live Science.
In the study, the researchers looked at the health data from about 700,000 people who were admitted to Swedish hospitals between 1973 and 2009. This population included more than 70,000 people with schizophrenia, people with 10 other major psychiatric disorders, and people with chronic physical illnesses such as Crohn's disease, diabetes or multiple sclerosis.
The researchers also reviewed data from marital records and other sources, to look at mating patterns among the people with psychiatric conditions, and among those with physical illnesses. [5 Controversial Mental Health Treatments]
It turned out that people with psychiatric disorders were more likely to marry and have children with people with either the same disorder as they had or a different psychiatric disorder, than they were to marry and have children with people without psychiatric disorders.
However, the researchers did not find the same mating pattern among people with physical illnesses. For example, people with Crohn's disease were not more likely to marry or have children with other people who had Crohn's disease or people who had another serious physical illness, such as diabetes.
The new study shows that "people with severe psychiatric disorders tend to mate with each other, and are less likely to mate with people without psychiatric disorders," said Scott Wetzler, a psychologist and behavioral scientist at Montefiore Health System in New York who was not involved in the study.
People with severe psychiatric disorders tend to have a very hard time establishing social relationships with others in general, and people without psychiatric conditions are less willing to marry people with such conditions, Wetzler told Live Science. These two factors also might help to explain the new results, he said.
Though the exact reasons behind the new findings remain unclear, the results are "very important to consider when doing future genetic research and when thinking about the higher incidence of psychiatric illness running in families," said Dr. Matthew Lorber, acting director of child and adolescent psychiatry at Lenox Hill Hospital in New York City, who was not involved in the study.
Wetzler agreed, saying that if two people who both have psychiatric conditions have a child together, the risk that the child also having the condition is increased.
The new study was published today (Feb. 24) in the journal JAMA Psychiatry.