Depression appears to be associated with a molecular-level disturbance in the body’s 24-hour clock, new research suggests.

Scientists examined genes that regulate circadian rhythm in people with and without a history of depression. As a group, those with a history of depression had a higher level of activity of the so-called Clock gene, which has a role in regulating circadian rhythm, than did people with no mood disorders.

Higher expression levels of this gene suggest something is amiss in the body’s 24-hour biological and behavioral cycle, which could affect sleep patterns and other physiological functions governed by circadian rhythm. Sleep disturbance is a common symptom of depression.

But the researchers noted that the association between the gene activity and depression is just that—a link, with no demonstrated causal effect in either direction. At this point in what is known about the relationship, this genetic profile could lead to depression or depression could alter this particular gene function, or some other biological or environmental influences could combine to disrupt the circadian clock.

Though this study offers just a snapshot in time of circadian activity in people with and without depression, the finding could have important clinical implications if it is supported by additional research. People with depression who share this genetic profile might benefit most from sleep-related treatments, such as light therapy or a class of antidepressants that act on melatonin, a hormone that regulates sleep.

The research is published in a recent issue of the Journal of Affective Disorders.