A new study from Aarhus University reveals that the majority of individuals diagnosed with mental disorders do not have a family history of the same illnesses. The research, published in The Lancet Psychiatry, analyzed data from over three million people in Denmark between January 1970 and December 2021.

The study, led by Professor Carsten Bøcker Pedersen, utilized pseudonymized data from Danish registries to link individuals and their mental health diagnoses across generations. The findings indicate that a significant portion of mental disorders arise in individuals without any first- or second-degree relatives having a history of the same condition.

Specifically, the study found that 89% of individuals diagnosed with schizophrenia have no immediate family members (parents, siblings, children) or second-degree relatives (grandparents, aunts, uncles, nieces, nephews) with the disorder. Similarly, 93% of individuals with borderline personality disorder have no such family history.

Even with depression, a common mental illness, the study showed that 60% of individuals who develop the condition do not have relatives with a history of the disease. This suggests that while genetics may play a role in the development of some mental disorders, many cases arise without a clear familial link.