A new report provides a more detailed picture of depression’s genetic influence.

Observers long ago noted that individuals whose immediate family had an abnormally high instance of mental illness were more likely to experience it themselves. The science of genetics also implies such an influence, and it now seems that a family history of depression and anxiety renders a subject’s symptoms more severe and more difficult to treat than that of those with no family history of the disorders. 

Researchers in New Zealand recently drew on a massive data trove drawn from 981 people who were tracked from infancy for a period totaling nearly three decades. One of the survey’s intentions was to discern the influence of genetics on the most common disorders: major depression, chronic anxiety and alcohol or drug addiction. Researchers used treatment history statistics to determine how much genetic tendencies affected severity, recovery and early onset rates.

While family history could not predict the age at which affected subjects first developed their conditions, it did carry a great degree of influence over every other variable, particularly rates of recurrence and severity of symptoms. The more often depression appeared in a subject’s genealogy, the more severe his or her own disorder would usually be. Its lifetime prevalence would be greater as well, meaning that a subject with a great number of affected family members was far more likely to lapse back into depression or addiction after a recovery period.

This study is most significant in noting that treatment plans for those whose families have long been affected by mental illness are usually longer and more intense than those of unaffected parties. Disorders encoded in one’s genes are more resistant to treatment. Subjects with established histories of recurrent or severe depression, anxiety or substance abuse problems would almost certainly benefit from a family history screen so doctors can better determine how to approach each individual case; the study of those who came before us helps to predict which treatments will ultimately be most effective.