Etiology of depression in children.

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.

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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).

Biological Factors

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. One study found the prevalence of MDD in first degree relatives to be two-fold in comparison to non-affective psychiatric controls and to psychiatrically ill controls that were never used (Cichetti and Toth, 1998).

"Top down" studies approach the child through the parents with a diagnosis of Major Depressive Disorder. In studies conducted to compare the prevalence of MDD in offspring of depressed parents with psychiatric or medical control groups, a two-fold increase was found (Rice, Harold and Thapar, 2003). Consistent scientific evidence supports the hypothesis that childhood depression is both familial and inherited from both bottom-up and top-down studies.

Another biological factor affecting the determination of Major Depressive Disorder centered on the prefrontal cortex in the brain. The prefrontal cortex plays a critical role in the regulation of mood. Certain abnormalities in the prefrontal cortex have been identified and implicated in the pathogenesis of Major Depressive Disorder (Nolan, Moore, Madden, Farchione, Bartoi, Lorch, 2002). Children who were diagnosed with Major Depressive Disorder, but had no history of familial MDD, had significantly larger left-sided, but not right-sided, prefrontal cortical volumes as compared to children with familial Major Depressive Disorder and a control group. In the same study, left-sided and right-sided prefrontal cortical volumes did not differ significantly between children who had a family history of Major Depressive Disorder and children in the control group (Nolan et al., 2002). Although the size of the prefrontal cortex may be a determining factor in the onset of Major Depressive Disorder, it is important to bear in mind that other factors, non-biological in nature, also may cause MDD.

Certain brain chemicals, called neurotransmitters, play an important role in regulating moods and emotions, providing further evidence of a biological etiology for Major Depressive Disorder. Neurotransmitters involved in depression include norepinephrine, dopamine, and serotonin. Medical research as early as the 1960's suggested that depression results from lower than normal levels of these neurotransmitters in parts of the brain. Supporting evidence for this theory was found in research on the effects of antidepressant drugs, which work by increasing the level of neurotransmitters in action during depression. Later medical studies have suggested a more complex relationship between neurotransmitter levels and depression (Nolan et al., 2002).

Interest in the role of gender has produced evidence that gender may be a contributing factor in depression. A greater prevalence of both depressive symptoms and diagnosable major depression has been noted in females as compared to males (Silberg, Pickles, Rutter, Hewitt, Simonoff, Maes, 1999). Although the rates of depression are reported to be approximately the same in boys and girls before adolescence, and slightly elevated in boys at pre-pubescence, the predominance of depression among girls is well established by mid-adolescence, and continues into young adulthood and middle age. The biological factors implicated in this difference focus on the role of reproductive hormones. An association has been found between hormonal concentrations and negative affect that elevates the risk for a diagnosis of Major Depressive Disorder in children (Silberg et al., 1999). From a developmental perspective, it seems especially important to recognize gender differences in depression because knowledge of gender-specific pathways may not only enhance knowledge about the etiology, but may also assist in developing preventative approaches.

Hydrocortisone is another hormone that plays a role in depression. According to medical research, many depressed individuals have higher than normal levels of hydrocortisone (cortisol), ahormone secreted by the adrenal gland in response to stress. In addition, general medical research has shown that an underactive or overactive thyroid gland can also lead to depression (Silberg et al., 1999).

Depression has been linked to a variety of other medical and biological conditions. These include dietary deficiencies in vitamin B6, vitamin B12, and folic acid; degenerative neurological disorders; strokes in the frontal part of the brain; and certain viral infections, such as hepatitis and mononucleosis. Specific medications such as steroids may also increase the likelihood of depression in people who have a predisposition due to heredity (Nolan et al., 2002).

Psychological Factors

Psychological theories of depression focus on the way people think and behave. In an essay written by Sigmund Freud in 1917, Freud explained melancholia, or major depression, as a response to loss--either real loss, such as the death of a loved one, or symbolic loss, such as the failure to achieve an important goal. Freud believed that a person's unconscious anger over loss weakens the ego, resulting in self-hate and self-destructive behavior (Freud, 1917/1959).

Cognitive theories of depression emphasize the role of irrational and illogical thought processes. American psychiatrist, Aaron Beck, proposed that depressed individuals tend to view themselves, their environment, and their future in a negative light because of their own errors in thinking. These errors include focusing on the negative aspects of any situation, misinterpreting facts in negative ways, and blaming themselves for any misfortune. In Beck's view, people learn self-defeating ways of looking at the world very early in their childhood. Erroneous thinking exacerbates the negative aspect of a given situation, which increases the risk of depression, particularly in highly stressful situations (Beck, 1979).

In support of this cognitive view, individuals with depressive personality traits appear to be more vulnerable to Major Depressive Disorder than others. Examples of depressive personality traits include gloominess, pessimism, introversion, self-criticism, excessive skepticism, and criticism, deep feelings of inadequacy, and excessive brooding and worrying. In addition, those individuals who regularly behave in hostile, dependent and impulsive ways appear to be at greater risk for depression, and tend to seek out and become involved in situations in which they can be hostile and dependent. (Beck, 1979).

American psychologist, Martin Seligman, proposed that depression stems from "learned helplessness", an acquired belief that one cannot control the outcome of events. For persons experiencing this state of mind, prolonged exposure to uncontrollable and inescapable events leads to significant apathy, pessimism, and loss of motivation. An adaptation of this theory by another American psychologist, Lynn Abramson, argues that depression results not only from helplessness, but also from hopelessness. The hopelessness theory attributes depression to a pattern of negative thinking in which people blame themselves for negative life events, view the causes of those events as permanent, and over-generalize specific weaknesses as applying to many areas of their life (Seligman, 1975).

No relatively recent research studies have been conducted in this area for Major Depressive Disorder. Although studied extensively, current empirical research in MDD has focused primarily on genetics and significant negative or stressful life events.

Environmental Factors (Stressful Life Events)

Psychologists agree that stressful experiences can trigger depression in children, especially those already predisposed to the illness. For example, the death of a loved one may trigger depression. True depression is usually distinguishable from grief, a normal process of mourning a loved one who has died. Other stressful experiences or negative life events may include divorcing parents, moving to a new school, addition of a sibling, and hormonal changes during puberty. Children who experienced physical or sexual abuse tend to be quite vulnerable to depression. So, too, do children living under chronically stressful conditions, such as a single parent home with many children and little or no support from friends or relatives. Social factors, including negative life events, and the interaction with pubertal status seem to account for more of a variance in negative affect than biological factors alone (Silberg et al., 1999).

Findings from several studies have shown that children and adolescents can develop Major Depressive Disorder from experiences associated with academic underachievement and poor psychosocial functioning (Eley, 1997). Their diminished self-concept and perceived efficacy, when they compare themselves to their peers, can directly impact their mood. A common environment impacts the etiology of abnormality (Eley, 1997).

There is also evidence that social roles and expectations, which have been identified as one of the most significant of early onset life events, comprise an etiological factor contributing to the diagnosis of Major Depressive Disorder (Brown, 2002). Brown contended that the origin of depression is closely linked to the quality of core social roles. The meanings children apply to these experiences play a central etiological role in the development of Major Depressive Disorder.

Social roles and expectations differ in boys and girls. One study found that boys and girls seem to have similar depressive responses to increased quarreling between parents, parent becoming less interested or less loving, parent becoming more nagging, failing grades on a report card, and actually failing a grade (Silberg et al., 1999). The same study showed that for girls, breaking up with a boyfriend was more likely to cause depressive symptoms than in boys. However, failing to make an athletic team or losing a close friend through arguments was more likely to lead to depression in boys.

Depression scores show a steady increase after age 11 years for both girls and boys who have experienced at least 1 or more negative life events. However, the mean depression score is still higher for girls, particularly for older girls (Silberg et al., 1999). In the same study, the age distribution of depression scores is nearly flat for those boys who have not experienced a notable past year life event. For girls, the increase in depression is still quite evident. This finding supports the interaction of biological and psychological factors as a key factor in the development of Major Depression Disorder.

Conclusion

Major Depressive Disorder is experienced by a significant proportion of young people, and can produce long-lasting detrimental effects (Rice et al., January 2002). Because Major Depressive Disorder has such a marked influence on a child's life, the question of etiology is raised. Three specific areas were examined for etiological evidence of determinants for MDD: biological factors, psychological factors, and environmental factors. Based on this research, depression is far more often a result of the interaction between a person's biological and psychological vulnerabilities and a stressful life event (Cicchetti and Toth, 1999). It is difficult to separate the impact of one factor, either biological, psychological or environmental, from that of the other factors; they partner together in the etiology for Major Depressive Disorder in children.

References

American Psychological Association. (2002). Diagnostic and statistical manual of mental disorders (4th Edition, Text Revision) (DSM-IV-TR). Washington, DC: Author.

Beck, Aaron T. (1979). Cognitive theory of depression. New York: Guilford Press.

Cicchetti, D. and Toth, S. (1998). The development of depression in children and adolescents. American Psychologist, 53 (2), 221-241.

Eley, T. (1997). Depressive symptoms in children and adolescents: Etiological links between normality and abnormality. Journal of Child Psychology and Psychiatry, 38. 861-865.

Freud, Sigmund. (1959). Collected papers. (Joan Riviere, Trans.). New York: Basic Book. (Original works published from 1856-1939).

Nolan, C., Moore, G., Madden, R., Farchione, T., Bartoi, M., Lorch, E., et al. (2002). Prefrontal cortical volume in childhood-onset major depression. Archives of General Psychiatry, 59, 173-179.

Rice, F., Harold, G., Thapar, A. (January 2002). The genetic aetiology of childhood depression: A review. Journal of Child Psychology and Psychiatry and Allied Disciplines, 43(1), 65-79.

Rice, F., Harold, G., Thapar, A. (November 2002). Assessing the effects of age, sex, and shared environment on the genetic aetiology of depression in childhood and adolescence. Journal of Child Psychology and Psychiatry and Allied Disciplines. 43(8), 1039-1051.

Rice, F., Harold, G., Thapar, A. (2003). Negative life events as an account of age-related differences in the genetic aetiology of depression in childhood and adolescence. Journal of Child Psychology and Psychiatry and Allied Disciplines, 44(7), 977-987.

Scourfield, J., Rice, F., Thapar., A, Harold, G., Martin, N., and McGuffin, P. (2003). Depressive symptoms in children and adolescents: Changing aetiological influences with development. Journal of Child Psychology and Psychiatry, 44(7), 968-976.

Seligman, Martin. (1975). Helplessness in depression, development, and death. San Francisco: Scribner Publishing.

Silberg, J., Pickles, A., Rutter, M.. Hewitt, J., Simonoff, E., Maes, H., et al. (1999). The influence of genetic factors and life stress on depression among adolescent girls. Archives of General Psychiatry, 56, 225-232.