The size of the hippocampus varies from one person to another regardless of depression, much like height and foot size vary. Several studies indicate that genetics determines about half of the size variation in the hippocampus.
We have some clues as to which genes determine this variation. One gene in particular, called brain-derived neurotrophic factor, or BDNF, has a variant that has been associated with a smaller hippocampus in at least four studies.
BDNF belongs to a family of genes that influence brain growth, stimulating it like fertilizer in a garden. Antidepressants may act in part by increasing BDNF fertilization in the hippocampus.
Other genes in the BDNF family are currently under study for their potential role in depression. This family of genes might influence how stress impacts the hippocampus, exacerbating the effects in some cases, while warding them off in others.
So what is the message for Laura and others like her? The decision to take an antidepressant can be a complex one, and each patient's unique situation needs to be considered. However, one consideration is that depression is associated with a smaller hippocampus, delayed treatment might be associated with further shrinkage, and antidepressants may have a positive impact on this brain region.
Dr. James Potash is an associate professor of psychiatry and co-director of the Mood Disorders Program (http://www.hopkinsmedicine.org/moods) at the Johns Hopkins School of Medicine in Baltimore. If you have questions or comments, please e-mail at firstname.lastname@example.org. To participate in our genetic and clinical studies, call 1-877-MOODS-JH.