Major Depressive Disorder (MDD) is experienced by a significant proportion of youth today, occurring at an earlier age than found in previous generations. Major Depressive Disorder can produce long-lasting detrimental effects on a child's life, which raises the question of etiology. Three areas were examined for evidence identifying specific determinants of Major Depressive Disorder in youth: biological factors, including studies on inherited characteristics; psychological factors, focusing on cognitive and affective activity; and environmental factors, such as stressful life events. The implications of the findings were then explored.
The term depression is often used to describe the temporary sadness, loneliness or "blues" that almost everyone feels from time to time. However, the DSM-IV TR (Diagnostic and Statistical Manual of Mental Disorders, 4th edition, Text Revised) defines Major Depressive Disorder (MDD) as a mental illness in which a person consistently experiences deep, unshakable sadness and diminished interest in all activities for a period of at least 2 weeks. Major Depressive Disorder dramatically impairs an individual's ability to function in one or more areas of his or her life. Persons with MDD usually experience feelings of despair, hopelessness, worthlessness, difficulty thinking or concentrating, and sometimes thoughts of committing suicide. Depression is one of the most common mental illnesses.
Although depression has long been a diagnosis made for adults, it has become increasingly prevalent in the youth of today. Mental health practitioners are seeing a marked increase in the number of youth who are experiencing depression at an earlier age than did previous generations (Cicchetti and Toth, 1998). Depressive symptoms and disorder are found in a significant proportion of young people, with long-lasting detrimental effects (Rice, Harold and Thapar, January, 2002). Major Depressive Disorder, having such a definitive impact on a child's life, raises the question of etiology. Three major areas will be explored as to the cause of depression in children, including biological factors, psychological factors and environmental factors.
Some depressions seem to occur suddenly, even when life appears to be going very well. Others have an obvious external cause such as a relationship conflict, financial difficulty or some personal failure. Yet many individuals experiencing these problems do not become depressed. In an attempt to identify causal factors, it has been hypothesized that depression results from the interaction between a person's biological and psychological vulnerabilities and a stressful life event (Cicchetti and Toth, 1998).
Depression has been found to run in families (Rice, Harold, Thapar, November, 2002). By studying twins, researchers have found evidence of a strong genetic influence in depression. Genetically identical twins raised in the same environment are three times more likely to both have major depressive disorder than are fraternal twins, who have only about half their genes in common. In addition, identical twins are five times more likely to have bipolar disorder in common. Bipolar disorder is characterized by alternating manic and depressive mood swings. These findings suggest that vulnerability to depression can be inherited. Adoption studies have found that children of depression are vulnerable to depression even when raised by adoptive parents, offering more evidence of a genetic role in depression. A consensus that Major Depressive Disorder is both familial and inheritable is evident in the findings from both twin and family studies (Rice et al., January 2002).
Family studies of early onset Major Depressive Disorder can be differentiated by the research methodology utilized (Scourfield, Rice, Thapar, Harold, Martin and McGuffin, 2003). "Bottom-up" studies evaluate the inheritability of Major Depressive Disorder by examining the child and working back through the child's ancestry. …