Depression is a serious medical illness that is often difficult to diagnose and treat. Studies on patterns of depression within families suggest that inherited genes may cause a predisposition to the disorder. People with early onset depression often have more relatives with depression than people whose depression does not begin until later in life. It is likely that several interacting genes cause this tendency towards the disorder, rather than one specific gene. This study will serve to identify particular genes that may cause a susceptibility to depression in order to better understand the brain mechanisms involved with severe depression. In turn, this may aid in the development of new treatments for depression.

Participation in this observational study will entail one interview and one blood test. Participants will be interviewed, either in person or by telephone, about their personal and family psychiatric history. The blood sample will be collected at a time and location that is convenient for the participant. Participants may also be asked to invite other family members to participate in the study.