To better understand the nature of the genetic link between bipolar illness and severe depression, other diseases outside those that affect mood could help. For a study, researchers sought to comprehend the connection between major depression (MD) and bipolar disorder (BD) genetic liabilities.

With follow-up until December 31, 2018, cohort research was undertaken using the information on people with Swedish parents who were born in Sweden between 1960 and 1990. The information comprised family genetic risk scores for MD and BD as well as ICD-10 codes for a variety of illnesses as reported in general care, specialty, and hospital registries. Data analysis was carried out between April and July 2022. Being in the higher and lower two risk deciles, respectively, was used to characterize high and low genetic liability. Individuals with high genetic liability to MD only, BD only, both MD and BD, high genetic liability to BD and low genetic liability to MD, and high genetic liability to MD and low genetic liability to BD were compared for risk. Risk for schizophrenia, other nonaffective psychoses, anxiety disorders, obsessive-compulsive disorder, schizoaffective disorder (SAD), nonpsychotic MD and BD, and psychotic MD and BD.

A total of 2,736,950 people’s data were included, with a follow-up age mean (SD) of 43.9 (9.1) years. The risk for nonpsychotic BD, psychotic BD, and SAD increased with a high genetic predisposition to just BD. The highest correlation between risk for nonpsychotic BD, anxiety disorders, and nonpsychotic MD was shown in patients with high genetic susceptibility to both BD and MD. A higher risk for psychotic BD, nonpsychotic BD, and SAD, with no increased risk for nonpsychotic MD or anxiety disorders, were associated with high genetic liability to BD and low genetic liability to MD. Anxiety disorders, nonpsychotic MD, and nonpsychotic BD are all more likely in those with high genetic liability to MD and low genetic liability to BD, whereas psychotic BD is not more likely.

Neither the genetically different BD nor the genetically close-related MD theories were validated by the investigation. Genetic susceptibility to mood disorders was linked to both BD and MD. However, even the susceptibility was somewhat selective. However, those with enhanced genetic BD liability had a much higher risk for psychosis than those with high genetic MD liability. Individuals at high genetic risk for MD exhibited a significantly increased risk for anxiety disorders compared to those at high genetic risk for BD. Examining risk profiles for various disorders could significantly help elucidate the genetic relationships between psychiatric syndromes.